2.      Mesenchymal and Melanocytic Tumours

Mesenchymal tumours are often malignant, with fibrosarcomas in particular being regularly observed. Chronic skin injuries, for example as a result of self-mutilation or injuries inflicted by other birds, are considered predisposing factors for the development of such sarcomas.

Clinically and cytologically, it is often difficult to distinguish granulation tissue from a sarcoma, particularly in the case of extensive or firm lesions.

Cytology may reveal highly activated and atypical-looking fibroblasts, which can also occur as part of physiological wound healing processes. In such cases, histopathological examination is the method of choice for further investigation.

Haemangiosarcomas and melanocytic tumours are rare in ornamental birds. Here too, histopathological examination is essential for assessing malignancy.

Benign mesenchymal tumours include haemangiomas, fibromas and lipomas. The first two entities are often difficult to assess cytologically, as only a small number of cells can be obtained from cavernous and firm tissues. Lipomas, on the other hand, are readily amenable to cytological examination, as adipocytes can be easily aspirated. However, histopathological examination is also required here for a definitive assessment, particularly to distinguish the lesion from the surrounding tissue.

3.      Round Cell Tumours

Malignant lymphoma is the most common round cell tumour of the skin. The diagnosis can be established by cytological or histopathological identification of an atypical lymphoid cell population. An exclusively cutaneous manifestation is rare; in most cases, systemic disease is already present at the time of diagnosis.

While a viral aetiology (Gallid alphaherpesvirus 2) is known in chickens, no corresponding association has so far been demonstrated in ornamental birds.

 

Non-neoplastic Skin Lesions

In addition to neoplasms, non-infectious inflammatory processes can also present as nodular lesions.

1.    Non-infectious

1.1 Feather Follicle Cysts
Feather follicle cysts are non-neoplastic skin lesions that occur particularly frequently in budgerigars and certain canary breeds (Fig. 3). They often have a high recurrence rate and may occur as multiple lesions. A developmental disorder, possibly of genetic origin, is considered to be the underlying cause. Cytologically, abundant keratin can usually be aspirated, while histologically, dilated feather follicles with marked hyperkeratosis are observed.

1.2 Polyps
Polyps are benign proliferations of the mucous membrane or skin, consisting of differentiated epithelium and underlying connective tissue. They often occur in association with chronic inflammation and particularly affect the oral cavity, eyelids and cloacal region.

1.3 Gout and Pseudogout
Both conditions are characterised by the deposition of metabolic products in the joints and can present clinically as nodules. Gout involves urate deposits, while pseudogout involves calcium crystals.
In advanced cases, material can be aspirated and differentiated cytologically. Histological examination may only be possible to a limited extent depending on the location, but can provide additional information in easily accessible lesions.

1.4 Xanthomas
Xanthomas are focal to multifocal accumulations of lipid-laden macrophages, frequently occurring in the breast and wings. Clinically, they appear as yellowish-orange, firm thickenings. They are often associated with elevated blood lipid levels, for example as a result of a high-fat diet. Diagnosis is made cytologically or histologically. An important differential diagnosis is mycobacteriosis, which should be investigated using special stains (see below).

2.      Infectious

Infectious diseases can also be associated with nodular skin lesions.

2.1 Abscesses
Following skin injuries, bacterial infections can lead to abscess formation. Cytologically, numerous intact or degenerated heterophilic granulocytes can be observed. Histologically, the diagnosis can be confirmed by identifying a pyogenic membrane and a capsule-like boundary.

2.2 Avian Pox
Infections with avipoxviruses occur in many bird species and show a high degree of host specificity. Featherless areas of the skin are preferentially affected. A pronounced epithelial proliferation is characteristic, although secondary bacterial infections can complicate the appearance.This makes cytological assessment more difficult, meaning that histopathological examination of biopsies taken from the edge of the lesion is the method of choice. Large eosinophilic cytoplasmic inclusion bodies are diagnostically characteristic (Fig. 4); PCR testing can be used to confirm the aetiology.

2.3 Mycobacterial Granulomas
Mycobacterial infections can generally lead to systemic infections with organ involvement (lungs, liver, intestines), but local cutaneous lesions can also occur (Fig. 5). These pathogens are zoonotic, and detection in both birds and mammals is subject to mandatory notification under the German Animal Diseases Notification Regulation (TierSeuchMeldV). Using Ziehl–Neelsen staining, acid-fast bacilli can be detected both cytologically and histologically in the cytoplasm of macrophages and in necrotic material from caseous lesions. Further differentiation of the pathogens (e.g. by culture or PCR) is of interest in order to better assess their zoonotic potential.

Conclusion

A wide range of diseases can manifest as nodular skin lesions, and clinically distinguishing a neoplastic process from inflammation or infection can be challenging. When interpreted in the clinical context, cytological examination of smear preparations and histopathological evaluation of tissue samples from representative affected sites are the gold standard for differentiating these lesions.

 

Dr. Kathrin Jäger

Services Related to This Topic

• Cytology / cytology requiring additional processing
• Histopathology / histopathology requiring additional processing
• Bacteriology (aerobic/anaerobic)
• Mycobacteria (Ziehl–Neelsen staining, culture, PCR)
• Pathogen detection by PCR (e.g. mycobacteria, avipoxvirus, herpesviruses)

The sample requirements described below refer to the analytical methods currently used by Laboklin for the measurement of various analytes. As analytical methods continue to evolve, these requirements may change over time. If in doubt, contact our laboratory before sample collection.
As a general rule, marked haemolysis and lipaemia should be avoided. Common causes of haemolysis include prolonged venous occlusion, difficult venepuncture, clotting in the refrigerator, and failure to separate serum or plasma before shipment. Fasting blood samples are generally recommended for hormone measurements to minimise lipaemia.

 

Thyroid Gland

T4 (Total T4, TT4; Free T4, fT4) and T3

Indications: Screening for hypothyroidism; screening and diagnosis of hyperthyroidism.

Important considerations before sample collection: T4 concentrations may be reduced by non-thyroidal illness (NTI) and by various medications. Free T4 is somewhat less affected by these factors, but its concentration may also be decreased by NTI and certain drugs. Differentiation from genuine hypothyroidism requires further diagnostic investigation.

Analytical methods: Measurement can be performed using two different methods.

1. CLIA (Chemiluminescent Immunoassay): This assay is based on the immunological binding of the T4 molecule. For initial screening, this more cost-effective method is often sufficient.
2. LC-MS/MS (Liquid Chromatography-Tandem Mass Spectrometry): This method is increasingly regarded as the gold standard. It is considered particularly precise because it measures only the T4 molecule itself, thereby avoiding interference from metabolites or antibodies. At Laboklin, LC-MS/MS testing is available for T4, T3 and rT3 (see below).

Sample material: Serum (mandatory for LC-MS/MS; preferred for CLIA).

Good to Know: TT4 and fT4 remain stable at room temperature for three to five days. For fT4 it is being discussed that dissociation of T4 from its binding proteins may occur after more than five days and/or when exposed to high ambient temperatures. This may result in elevated fT4 concentrations, potentially leading to misinterpretation of results.

TSH

Indications: Investigation of hypothyroidism; treatment monitoring.

Important considerations before sample collection: In the presence of a low T4 concentration and compatible clinical signs, an elevated TSH concentration generally confirms hypothyroidism. However, approximately 30% of hypothyroid dogs have low TSH concentrations. In such cases, further diagnostic investigations are required to differentiate between NTI and hypothyroidism.

Analytical method: CLIA

Sample material: Serum

Good to Know: TSH is stable for 24 hours at room temperature and for seven days when refrigerated (2 to 8°C).

Reverse T3 (rT3)

Indications: Aid in differentiating between NTI and hypothyroidism in dogs with reduced T4 concentrations and no increase in TSH; support in cases of suspected hyperthyroidism in cats when T4 concentrations are not elevated as expected.

Important considerations before sample collection: rT3 is a highly promising parameter. However, interpretation should always be performed in the clinical context and in combination with other thyroid parameters.

Analytical method: LC-MS/MS

Sample material: Serum

Good to Know: rT3 remains stable at room temperature for up to 14 days.

Autoantibodies (against Thyroglobulin, T3 and T4)

Indications: Suspected interference with T4 measurement by CLIA; breeding health screening and breeding approval programmes.

Important considerations before sample collection: Immunosuppression (medication) and immune stimulation (for example vaccination) may alter antibody concentrations. This should be taken into account when interpreting results.

Analytical method: ELISA. Results are reported either quantitatively (percentage proportion in the sample) or qualitatively (positive/negative).

Sample material: Serum

Good to Know: Antibodies are relatively stable. However, samples should be transported refrigerated if transport times exceed 48 hours. Sample quality is particularly important for antibody testing. Serum must be cleanly separated, and haemolysis and lipaemia must be avoided.

 

Parathyroid Gland

Parathyroid Hormone (PTH)

Indications: Investigation of hyperparathyroidism or hypoparathyroidism.

Important considerations before sample collection: As interpretation depends on correlation with the blood calcium concentration at the time of sampling, PTH and calcium should be measured from the same serum sample or from serum collected at the same sampling time.

Sample material: Serum

Analytical method: CLIA

Good to Know: PTH is unstable. Consequently, proper pre-analytical handling is of great importance. The sample should be allowed to clot for no longer than 30 minutes, then centrifuged immediately and the serum transferred into a separate tube. The separated serum must be stored and transported frozen. At a minimum, shipment should be carried out using pre-frozen cooling packs; transport on dry ice is ideal.

 

Adrenal Gland

Cortisol

Indications: Screening parameter for ruling out hypoadrenocorticism; measurement as part of the ACTH stimulation test and the dexamethasone suppression test.

Important considerations before sample collection: Cortisol secretion increases in response to both emotional and physical stress. This can affect the results of functional tests. In particular, the dexamethasone suppression test should be performed only after concurrent diseases have been resolved and under conditions that are as stress-free as possible.

Analytical methods: CLIA; LC-MS/MS may be used for specific clinical questions. In routine diagnostics, cortisol is generally measured using immunological assay methods (CLIA). In human medicine, however, LC-MS/MS is increasingly becoming established as a highly specific and precise method for cortisol measurement.

Sample material: Measurement can be performed using plasma. However, serum is preferred to ensure standardisation of hormone testing. In particular, the same sample material should always be used for follow-up measurements and functional tests to ensure consistent and comparable results.

Good to Know: Cortisol in serum samples is generally stable at room temperature for 3 to 5 days. Marked lipaemia may affect cortisol measurements performed using immunoassays. Although fasting is not strictly required for functional testing, it may be advisable to feed only a small and/or low-fat meal before testing in order to minimise lipaemia-related interference.

Urine Cortisol-to-Creatinine Ratio (UCCR)

Indication: Screening for possible Cushing’s syndrome.

Important considerations before sample collection: Urine samples for UCCR determination should ideally be collected in the morning and in a stress-free environment, with at least three (better five) days between sample collection and a veterinary visit. Before submission, urinary tract infection should be excluded by performing urinalysis, including sediment examination.

Analytical method: For one of the immunoassays widely used in veterinary medicine for urinary cortisol measurement (CLIA, Immulite 2000®, Siemens, Germany), changes made by the manufacturer to the assay substrate have led to concerns regarding the reliability of results obtained from canine urine samples. The assay used by Laboklin is not affected by this issue.

Endogenous ACTH (eACTH)

Indications: Further differentiation of Cushing’s syndrome and hypoadrenocorticism (Addison’s disease).

Analytical method: CLIA

Sample material: EDTA plasma

Good to Know: Endogenous ACTH is unstable in biological samples, particularly in dogs. It is rapidly degraded by endogenous enzymes in the blood, which may lead to falsely low results. When stored frozen at -20°C in separated plasma, eACTH remains stable for extended periods. Blood should therefore be collected into pre cooled EDTA tubes, ideally chilled in a freezer at -20°C before sampling. Centrifuge and separate immediately, transfer plasma to an uncoated tube and ship frozen. Ideally, the sample should arrive at the laboratory still frozen. Glass tubes are not suitable, as eACTH binds to glass surfaces, which can reduce the measured concentration.

Aldosterone

Indication: Investigation of hyperaldosteronism.

Important considerations before sample collection: The patient should be adequately hydrated, as the renin-angiotensin-aldosterone system (RAAS) is influenced by hypovolaemia and dehydration.

In azotaemic patients, measurement of aldosterone alone is not sufficient for the diagnosis of primary hyperaldosteronism, as aldosterone concentrations may also be elevated in renal disease. Feeding time can have an effect on the RAAS; therefore, collection of a fasting blood sample is recommended.

Sample material: Serum

Analytical method: LC-MS/MS. This method is considered highly precise and superior to immunological assay methods. It is important to note that LC-MS/MS typically measures lower aldosterone concentrations than other analytical methods. This has been taken into account in the reference intervals provided by Laboklin.

Good to Know: The sample should be as fresh as possible and no older than 48 hours. Allow to clot for ≤30 minutes, centrifuge immediately and transfer serum to a separate tube. The separated sample should be cooled as quickly as possible and must arrive at the laboratory under refrigerated conditions.

RAAS Profile (Calculation of Renin Activity, ACE Activity and the AA2 Ratio) 

Indication: Investigation of hyperaldosteronism in patients with concurrent azotaemia.

Important considerations before sample collection: The patient should be adequately hydrated, as the renin-angiotensin-aldosterone system (RAAS) is influenced by hypovolaemia and dehydration. Feeding time can have an effect on the RAAS; therefore, collection of a fasting blood sample is recommended.

Sample material: Serum

Analytical method: Renin activity is calculated following measurement of aldosterone, angiotensin I and angiotensin II by LC-MS/MS. The method has been validated for both cats and dogs.

Good to Know: Angiotensin I and angiotensin II are unstable and must not be exposed to temperatures of 4 to 8°C. Consequently, the sample must arrive at the laboratory frozen. The sample should be allowed to clot for no longer than 30 minutes, then centrifuged immediately and the serum transferred into a separate tube. The serum needs to be frozen immediately at -20°C. The sample must not be stored in a refrigerator prior to freezing and, once frozen, must not be allowed to thaw before arrival at the laboratory (!). Shipment on dry ice is mandatory. 

Catecholamines (Metanephrine, Normetanephrine)

Indications: Investigation of a pheochromocytoma or catecholamine-producing paraganglioma.

Important considerations before sample collection: Catecholamines are released in response to stress. Consequently, stressful situations may lead to increased catecholamine secretion. Urinary measurement is less affected by episodic catecholamine release than blood measurement. Urine samples may be collected either by cystocentesis or as a free-catch sample. Collection in the home environment is not mandatory. However, a urinary tract infection should be excluded before sample submission by performing a urinalysis, including sediment examination.

Medications such as phenoxybenzamine, metoclopramide, β-blockers, calcium channel blockers or sympathomimetics (epinephrine,
dopamine, dobutamine, phenylpropanolamine and terbutaline) may cause falsely elevated results. Particular attention should be paid to ensuring that sample collection takes place before initiation of any potential treatment with phenoxybenzamine.

Analytical method: LC-MS/MS

Sample material: EDTA plasma or urine (free-catch or cystocentesis sample)

Good to Know: Catecholamines are unstable in blood samples. Blood should therefore be centrifuged immediately and the plasma separated without delay. After transfer into an uncoated sample tube, the plasma should either be stored refrigerated at 4°C, where it remains stable for up to three days, or frozen at -20°C. Samples should be shipped under refrigerated conditions and must arrive at the laboratory chilled. Shipment with pre-frozen cooling packs is the minimum requirement; transport on dry ice is ideal. In urine, catecholamines remain stable for several days even at room temperature. The acidification of urine samples that was previously recommended is no longer performed. Studies in both human and veterinary medicine have demonstrated that acidification is not necessary.

 

Pituitary Gland

Insulin-Like Growth Factor 1 (IGF-1)

Indications: Acromegaly (hypersomatotropism) and pituitary dwarfism (hyposomatotropism).

Analytical method: CLIA

Sample material: Serum

Good to Know: The sample should be allowed to clot for no longer than 30 minutes, then centrifuged immediately and the serum transferred into a separate tube. Provided that the blood sample is centrifuged and separated promptly, IGF-1 remains stable for 24 hours at room temperature and for up to seven days at 4°C. Cooling of the sample and shippment under refrigerated conditions is recommended, especially if prolonged transportation times are expected.

 

Endocrine Pancreas

Insulin

Indication: Insulinoma

Important considerations before sample collection: Blood sampling should be performed during documented hypoglycaemia (blood glucose < 3.3 mmol/L or < 60 mg/dL). Glucose and insulin measurements must be performed on serum obtained from blood collected at the same time.
Ideally, collect blood from a large vessel (e.g. the jugular vein) using a large-bore needle to minimise haemolysis and facilitate rapid collection.

Analytical method: CLIA (dog), ELISA (cat)

Sample material: Serum

Good to Know: Insulin is unstable in serum at room temperature and may undergo significant degradation within a few hours. The blood sample should therefore be allowed to clot for no longer than 30 minutes, then centrifuged immediately and the serum transferred into a separate tube to minimise degradation. The sample should be stored refrigerated at 4°C. If analysis cannot be performed within 24 hours, freeze serum at -20°C (-80°C for long-term storage). Refrigerated shipment must be ensured using pre-frozen cooling packs; for longer transport times, shipment on dry ice is recommended. The sample should arrive at the laboratory refrigerated (4-8°C). As haemolysis may result in the release of insulin-degrading enzymes, it should be avoided whenever possible.

Jennifer von Luckner, Ruth Klein

 

Our Endocrinology Services Include

• Individual hormone assays
• Functional endocrine testing
• Specialised diagnostic profiles

This phase is not only therapeutic but also allows the clinician to define, for each individual patient:

• The baseline severity of the disease
• The minimum treatment required to maintain control
• The pattern and frequency of flares

Once the disease has been appropriately characterized, ASIT should be considered, as it is recommended in all patients with confirmed environmental AD, as the disease is typically

progressive, with increasing severity and frequency of flares over time.

Early initiation is desirable once diagnosis is secured, as the potential for long-term benefit is often greater in earlier stages and the likelihood of reducing or even eliminating the need for medication is higher when ASIT is introduced sooner.

ASIT can also be effective in chronic or severe cases, although in these patients the goal is usually improved control and reduced medication rather than complete remission.

Ultimately, the key is to balance early intervention with adequate diagnostic certainty and clinical characterization, ensuring appropriate case selection and meaningful evaluation of response.

Allergy testing: not for diagnosis, but for treatment design

Once the decision to initiate ASIT has been made, allergy testing is performed not to diagnose AD (allergy is a clinical diagnosis; see above) but to identify relevant allergens for inclusion in the immunotherapy formulation.

Both serological IgE and intradermal testing are suitable for this purpose. In clinical practice, serological testing offers clear advantages in terms of convenience and standardization.

However, the quality and specificity of the test are critical, as they directly influence allergen selection and, consequently, treatment efficacy.

High-quality assays should:

• Specifically detect allergen-specific IgE (avoiding cross-reactivity with IgG)
• Address the issue of cross-reactive carbohydrate determinants (CCDs), which can lead to clinically irrelevant false-positive results

The use of assays based on the high-affinity IgE receptor (FcεRIα), together with CCD detection and blocking systems, significantly improves the accuracy of allergen identification and supports a more precise and clinically relevant ASIT formulation.

Routes of administration of ASIT

Subcutaneous immunotherapy (SCIT) has traditionally been the standard route of administration. Over time, alternative routes have been explored with the aim of improving efficacy, accelerating the onset of clinical response, or facilitating administration.

The main available routes are outlined below.

Subcutaneous immunotherapy (SCIT): the classical route

Subcutaneous immunotherapy remains the most widely used and best-supported route in clinical practice.

It is typically introduced through a progressive induction phase, followed by maintenance therapy. With current protocols such as Artuvetrin®, induction is straightforward and allows reaching the full maintenance dose within the first three months of treatment.

This approach offers a well-established safety profile, flexibility for individual adjustment and extensive clinical experience. For these reasons, SCIT remains the preferred first-line approach in most patients.

Accelerated subcutaneous protocols:  rush and cluster approaches

Accelerated protocols aim to shorten the time nee-ded to reach maintenance.

Rush immunotherapy (RIT) involves administering multiple escalating doses over a short period, often within a single day. During this process, the cumulative allergen dose within a single day exceeds the standard maintenance dose, which contributes to a higher risk of adverse reactions.

For this reason, RIT requires close monitoring and is typically performed in a hospital setting.

Cluster protocols group injections into one or a few sessions, allowing faster progression to maintenance without exceeding the standard dose. Although published evidence is limited, clinical experience suggests that this approach may be a practical alternative in selected cases without the need for hospitalization. 

Sublingual immunotherapy (SLIT): an alternative, but with less evidence

Sublingual immunotherapy has been proposed as a non-invasive alternative administered daily via the oral mucosa. While some studies report clinical improvement, the available evidence is limited compared to SCIT, and its use is generally restricted to selected cases.

Intralymphatic immunotherapy (ILIT): targeted delivery with faster onset potential

Intralymphatic immunotherapy delivers allergens directly into lymph nodes, enabling direct antigen presentation. This targeted delivery allows direct antigen presentation, using lower allergen doses than conventional subcutaneous protocols and potentially accelerating the onset of clinical response.

This approach aims to enhance immune modulation, with studies suggesting a safe and faster onset of clinical effect. For optimal efficacy, ILIT should be performed under ultrasound guidance.

Practical message

The best route is not simply the newest one, but the one that best combines scientific support, safety, feasibility, owner adherence and conformity with the registered treatment protocol. For most patients, subcutaneous immunotherapy remains the most reliable and widely applicable approach, while alternative routes may be considered in selected cases. These alternative approaches are generally used off-label and should be supported by available scientific evidence, with preference given to treatments in accordance with the registered indications of the product.

What to expect: defining treatment success

One of the most important aspects of ASIT success is setting realistic and appropriate expectations.

ASIT does not produce an immediate effect. The immune system requires time to adapt, and clinical improvement may take up to 12 months or longer. For this reason, treatment should be maintained consistently before evaluating its efficacy.

Treatment response can be understood at different levels:

• Complete remission (excellent responders)
  Absence of clinical signs without the need for additional medication. This outcome is not exceptional and may be achieved in a substantial proportion of patients (around 50%) particularly when ASIT is introduced early and protocols are followed correctly.
• Good clinical improvement
  Reduction in pruritus, fewer flares, and decreased need for medication. This represents a large proportion of cases and is often considered a successful outcome in daily practice.
• Partial or limited response
  Less evident improvement, although ASIT may still contribute to better long-term control. In some patients, it may also help slow the progression of this chronic disease, even if the clinical improvement is less apparent.

Overall, when combining excellent responders and patients with meaningful clinical improvement, ASIT achieves clinical success in approximately 70–80% of cases, potentially higher with good compliance.

The importance of compliance and long-term management

The most common cause of perceived treatment failure is premature discontinuation or inadequate adherence to the protocol.

Because ASIT requires time to modulate the immune response: 

• Early discontinuation prevents its effect from developing
• Inconsistent administration reduces efficacy
• Poor clinical control may lead to the incorrect assumption that ASIT is ineffective

Appropriate symptomatic and proactive therapy should therefore be maintained as long as clinical signs are not fully controlled.

Evolution over time: adapting treatment to response

In patients responding to ASIT, clinical evolution should guide therapeutic decisions.

Over time:

• Flare frequency and severity decrease
• Medication requirements are progressively reduced
• Treatment can be adjusted to the minimum effective level of control

Importantly, the ASIT dose is generally maintained unchanged, while symptomatic therapy is adjusted. The intensity of this therapy should not be predefined, but adapted dynamically to the patient’s clinical evolution. This reflects the goal of ASIT: not only to control clinical signs, but to modify disease progression and reduce long-term treatment burden.

Clinical tip: How to explain ASIT to owners in practice

When introducing ASIT, clear communication is essential to ensure long-term compliance and treatment success. The following three messages are key:

1. “This is a long-term treatment, not a quick solution”
   ASIT does not act immediately. The immune system requires time to adapt, and the full effect may take up to 12 months or longer.

The goal is not rapid improvement, but long-term disease control.

2. “We will continue other treatments while ASIT starts working”
   Owners should understand that antipruritic and anti-inflammatory treatments are necessary to maintain comfort and will be adjusted progressively according to response, rather than discontinued at the start.

3. “Success does not always mean stopping all medication”
   Success can include:

• • Less itching
  • Fewer flare-ups
  • Reduced need for medication

Even without complete remission, improving disease control and quality of life is a successful outcome.

 

Conclusion

Allergen-specific immunotherapy is the only treatment capable of modifying the course of atopic dermatitis. Its success depends not only on correct allergen selection and protocol choice, but also on timing, individualization, and effective communication with the owner.

In clinical practice, ASIT is an important part of the long-term management of atopic dermatitis, and the key lies in its optimal implementation for each patient.

 

Carmen Lorente-Méndez

 

LABOKLIN Services

• Allergen-specific IgE testing (FcεRIα-based assays)
• Pax complete with allergen extracts and molecular components
• CCD blocking to avoid false-positive results
• Individualized ASIT formulations
• Support in interpretation and treatment planning

The recommended daily requirement is 1–2 mg/kg body mass, and at least 2 mg/kg body mass for sport horses. In cases of increased oxidative stress or muscular disease, 4–6 mg/kg body mass is recommended.

A chronic vitamin E deficiency can lead to severe neuromuscular diseases. These include vitamin E deficient myopathy with degenerative muscle changes, Equine Motor Neuron Disease (EMND) with progressive degeneration of motor neurones, and Neuroaxonal Dystrophy/Equine Degenerative Myeloencephalopathy (NAD/EDM), a neurodegenerative disease of young horses in which vitamin E deficiency is considered a key predisposing factor.

Vitamin status is assessed via serum α-tocopherol concentration; values above 2.0 µg/ml are considered adequate.

In the absence of grass intake, supplementation is mandatory. Natural RRR-α-tocopherol is superior to synthetic forms in terms of bioavailability.
However, supplementation beyond requirements does not show consistent benefits in healthy sport horses regarding performance or markers of oxidative stress.

 

Myopathies in Icelandic horses – laboratory diagnosis and clinical relevance

Myopathies are an increasingly recognised cause of reduced performance and non-specific lameness in Icelandic horses. Due to breed-specific biomechanical characteristics and subtle clinical signs, muscular disorders are often diagnosed late. A recently described chronic idiopathic myopathy appears to represent an Icelandic horse-specific entity.

Affected horses mainly show non-specific clinical signs such as reduced performance, diffuse lameness, stumbling, increased respiratory rate, and reduced willingness to perform certain gaits. Acute clinical signs of classical exertional rhabdomyolysis are usually absent.

Serum creatine kinase (CK) is the most important laboratory marker. Resting values are often normal or only mildly elevated. A diagnostically key finding is exercise-dependent CK increase, measured in a standardised manner at 4 and 24 hours post-exercise. Peak CK values typically range between 2000–3000 U/L and are therefore significantly lower than in horses with recurrent exertional rhabdomyolysis (RER).

CK kinetics have greater diagnostic value than single measurements. Reproducible, moderate post-exercise increases support a myopathic origin, even when absolute values are only mildly elevated. In addition, aspartate aminotransferase (AST) may be used to assess longer-standing muscle damage. Inflammatory parameters and metabolic routine profiles are primarily used to rule out systemic or inflammatory diseases.

Definitive diagnosis is confirmed via muscle biopsy from the semimembranosus muscle. Histopathology shows chronic degenerative and regenerative changes with centralised nuclei, without evidence of abnormal glycogen storage or myofibrillar defects.

In Icelandic horses with reduced performance, exercise-dependent CK kinetics should be included early in the diagnostic work-up. In combination with muscle biopsy, this enables reliable differentiation between myopathic and non-myopathic causes and provides a key basis for clinical decision-making.

 

Fever in horses: the role of laboratory diagnostics in clinical decision-making

Fever in horses is a common but non-specific clinical sign, the aetiological investigation of which requires a structured diagnostic approach (Fig. 1). The aim is the early identification of infectious or systemic diseases that require targeted treatment or further measures.

Following history-taking and clinical examination, laboratory diagnostics play a central role. Haematological and clinical chemistry tests allow an initial assessment of the inflammatory process as well as indications of possible organ involvement.
Acute-phase proteins are of particular diagnostic importance in this context. Serum amyloid A (SAA), as the horse’s major acute-phase protein, responds rapidly and with high sensitivity to inflammatory stimuli and is suitable both for detecting acute processes and for monitoring disease progression. Fibrinogen shows a delayed, longer-lasting increase and is particularly relevant in subacute or chronic inflammation. Due to their high sensitivity but lack of specificity, acute-phase proteins must always be interpreted in a clinical context.

For the aetiological investigation of infectious causes, specific laboratory diagnostic methods are required. Molecular detection techniques, in particular PCR-based methods in accredited laboratories, are considered the gold standard for direct pathogen detection. They are characterised by high analytical sensitivity and specificity and enable targeted differentiation of relevant bacterial and viral pathogens. Point-of-care tests can provide a rapid initial indication, but they neither replace comprehensive laboratory diagnostics nor quality-assured interpretation of results by specialised laboratories.

Depending on the laboratory findings and the clinical course, further diagnostic measures, including imaging techniques or targeted sampling, may be required. Overall, laboratory diagnostics represent an indispensable component of fever investigation in horses and form the basis for evidence-based treatment decisions as well as herd protection measures.

 

Genetic testing in equine myopathies: evidence-based application and genetic limitations

Genetic testing has become an established diagnostic tool in equine myopathies; however, it is currently carried out without binding regulatory oversight. This places veterinarians under the obligation to critically assess the validity of commercially available tests. A genetic test should only be used clinically if the underlying variant is demonstrably causally associated with the disease and meets internationally recognised validation criteria.

Fundamental requirements for valid genetic tests include a low allele frequency in the general population, a high genotype–phenotype concordance, a functionally relevant effect of the variant on the encoded protein, and reproducibility of results in peer-reviewed studies. To date, only a small number of genetic tests for equine myopathies meet these criteria.

Currently, there are five to six validated genetic tests for muscle disorders in horses, including polysaccharide storage myopathy type 1 (PSSM1; GYS1), myosin heavy chain myopathy (MYHM; MYH1), hyperkalaemic periodic paralysis (HYPP; SCN4A), malignant hyperthermia (MH; RYR1), and glycogen branching enzyme deficiency (GBED; GBE1).

Identification of the causal variants was based on strictly phenotyped case–control studies using gold-standard diagnostics such as muscle histopathology or electromyography. The respective mutations show a strong disease association, low prevalence in healthy populations, and a clear functional effect on the affected protein.

In contrast, there are commercial genetic test panels for so-called type 2 polysaccharide storage myopathies (PSSM2), myofibrillar myopathies (MFM), muscle integrity myopathy (MIM), and recurrent exertional rhabdomyolysis (RER). These tests are based on variants in genes such as MYOT, FLNC, MYOZ3, PYROXD1, CACNA2D3, and COL6A3, whose pathogenic relevance has not yet been convincingly demonstrated.

Several independent studies have failed to show a significant association between these variants and histopathologically confirmed myopathies. The prevalence of the tested variants was similar in affected horses and healthy controls, leading to high rates of false-positive and false-negative results.
Particularly notable is the high allele frequency of these variants in the general population: population genetic analyses show that up to 50% of Warmblood horses carry at least one of these variants. Given the much lower prevalence of clinically manifest muscle diseases, a causal role is unlikely; rather, these are probably benign genetic polymorphisms.

Evidence is also limited for the genetic diagnosis of recurrent exertional rhabdomyolysis. The so-called Px variant, which has been proposed as causal, is synonymous and does not lead to an amino acid change. Its high prevalence in healthy Thoroughbreds contradicts a causal pathogenic role.

In summary, genetic tests in equine myopathies should only be used when they are strictly validated and in agreement with breed, clinical presentation, and laboratory and histopathological

findings. Uncritical use of non-validated genetic test panels carries a significant risk of misdiagnosis and inappropriate selective breeding.

 

Development of new diagnostic tests for infectious endometritis in mares

Infectious endometritis is one of the most common causes of subfertility and infertility in mares. It occurs either as a persistent inflammatory response following covering or as a chronic bacterial infection. While the majority of mares effectively eliminate uterine bacterial contamination within 6–24 hours, approximately 10–15% develop chronic endometritis, which prevents successful pregnancy.

The classical diagnosis of infectious endometritis is based on bacterial culture, cytological examination, and molecular biological methods such as PCR. However, these methods primarily detect planktonic, metabolically active bacteria.
Recurrent infections may still occur because pathogens can persist either in anatomical reservoirs (e.g. the clitoral fossa), in a metabolically inactive (dormant) state deep within the endometrium, or as bacterial biofilms. These forms often evade both conventional diagnostics and antimicrobial treatment.

To detect dormant, persistent bacteria, a diagnostic–therapeutic activation concept has been developed, in which dormant bacteria in the endometrium are stimulated so that they can subsequently be detected using conventional culture or PCR and made accessible to treatment. This approach represents a significant advance in the diagnosis of subclinical and recurrent endometritis.

A previously unresolved diagnostic problem is the reliable in vivo detection of bacterial biofilms in the uterus. Biofilms effectively protect bacteria from the immune system and antimicrobial agents and promote the development of antimicrobial resistance. Although it has been experimentally demonstrated that common equine endometritis pathogens such as Streptococcus equi subsp. zooepidemicus, Escherichia coli, and Pseudomonas aeruginosa are capable of forming biofilms, there is currently no established clinical diagnostic method for uterine biofilms.

Current research approaches focus on detecting specific components of the biofilm matrix in low-volume uterine lavage samples. This matrix consists of proteins, lipids, polysaccharides, and nucleic acids. Proteomic and lipidomic analyses have already identified differences between planktonic and biofilm-forming bacteria, including biofilm-specific proteins and membrane lipids with potential diagnostic relevance. The aim is to develop a robust, clinically applicable test that enables targeted diagnosis and thus a differentiated, biofilm-specific therapy.

In summary, in cases of recurrent infectious endometritis, not only free-living bacteria but also dormant persistent organisms and bacterial biofilms should be considered in the diagnostic evaluation. The development of biofilm-specific diagnostic methods represents a crucial step towards optimising therapy and enabling more targeted and responsible use of antibiotics.

 

Jana Pohl

 

A selection of our services relating to the topics above:

• Individual vitamin analyses and vitamin profiles (basic and comprehensive)
• Basic and extended muscle screening
• Various PCR panels for pathogen detection by organ system (e.g. respiratory tract I–IV)
• A wide range of genetic tests (e.g. polysaccharide storage myopathy type 1 (PSSM1), immune-mediated myositis & MYH1 myopathy (MYHM), hyperkalaemic periodic paralysis (HYPP), equine malignant hyperthermia (EMH), glycogen branching enzyme deficiency (GBED))
• Breeding hygiene services

Further Reading

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In the same study, treatment success rates for chronic diarrhoea in dogs, cats, and horses ranged between 61–85%, and for chronic rhinitis in cats from 70% (8). In horses, autovaccines can also be used in cases of free faecal water (9).

In another study on idiopathic recurrent pyoderma in dogs, administration of a Staphylococcus pseudintermedius-based autovaccine in addition to antibiotic therapy resulted in significantly improved pyoderma scores compared with the antibiotic-only group (10). Success rates for this indication in further studies between from 77–88% (11–13).

Abscesses in rabbits caused by highly virulent S. aureus strains decreased in size within two weeks of autovaccine treatment, although they were not completely eliminated (14).

Unlike conventional vaccines, autovaccines do not contain adjuvants. The use of immunomodulators to enhance the cellular immune response prior to administration of autovaccines for staphylococcal infections has been described (6).

 

Mechanisms of action of autovaccines

Autovaccines do not act through direct elimination of the pathogen, but rather through a general stimulation of the immune system, enabling the host to eliminate the pathogen itself.

Sir Almroth Edward Wright already hypothesised an increase in phagocytic activity following autovaccine therapy (4, 5). Although the exact mechanism of action has not yet been fully clarified, it is assumed that the innate immune system is activated first, leading to a non-specific immune response and the recruitment of phagocytic defence cells such as macrophages to the site of infection.

This is followed by activation of the adaptive immune response, in which T and B cells are involved and both cellular and humoral defence mechanisms are triggered (6, 15). This distinguishes autovaccines from conventional vaccines, which primarily induce a humoral immune response (6).

Furthermore, it has been shown that autovaccine treatment increases the production of pro-inflammatory cytokines, thereby enhancing overall immune activity (16). Orally administered autovaccines, for example in cases of bacterial diarrhoea or other gastrointestinal infections, also lead to an increase in secretory antibodies (IgA), which protect the intestinal epithelium from bacterial adhesion and thereby strengthen the mucosal barrier (17, 18).

Interestingly, autovaccines may also influence the bacterial population targeted within the host. In one study, strains with a reduced genetic repertoire for survival in the host predominated after treatment (19). This may be advantageous for therapy.

 

Autovaccines at Laboklin

Autovaccines at Laboklin can be produced for companion animals that are not used for food production. Farm animals intended for food production are excluded.

The exact ordering process for an autovaccine consists of several steps, including the initial bacteriological examination, the required documentation, as well as manufacturing and dispatch (Fig. 1).

Autovaccines should not be administered to young animals under one year of age.

The routes of administration include injection vaccines for chronic skin or ear infections, inhalation vaccines for chronic respiratory infections, oral (swallow) vaccines for chronic diarrhoea, and combination vaccines with both oral and injectable components for infections of the urogenital tract.

An overview shows which autovaccine types are most commonly produced for the respective animal species depending on the clinical presentation (Fig. 2).

The administration period for the different autovaccines is usually 3–4 weeks. A prerequisite for production is completing the Laboklin prescription forms and, in Germany, the submission of the pharmacy authorisation for the veterinary practice’s in-house pharmacy.

An autovaccine can be produced when no commercially available vaccines exist against the pathogen. Regulation (EU) 2019/6 on veterinary medicinal products governs the manufacture, prescription, and supply of autovaccines at EU level (20). It also states that the attending veterinarian must ensure that the isolated pathogen is administered as an autovaccine only to animals belonging to the same epidemiological unit or, if at different locations, to those with a verified epidemiological link (21).

Once the legal requirements are fulfilled, the autovaccine is produced at Laboklin. To ensure quality and safety, this includes not only inactivation of the pathogens and adjustment of the microbial concentration, but also a two-week sterility control in accordance with the European Pharmacopoeia (22).

A maximum of four pathogens can be included in a single autovaccine. In general, autovaccines can be produced for aerobically growing bacteria, with the exception of aerobic spore-forming bacteria.
Obligate anaerobic bacteria, viruses, and fungi are also excluded.

Before manufacturing an autovaccine, it should be assessed whether the bacteria isolated in the microbiological examination are potentially pathogenic for the specific anatomical site. An autovaccine targeting commensal flora is not useful.

The six most common pathogens for each autovaccine type are summarised in an overview (Fig. 3). In cases of recurrence, a follow-up vaccine can be produced within one year using bacteria obtained from the microbiological examination. In some cases, a repeat bacteriological analysis is useful to determine the current spectrum of pathogens.

In particular, pyoderma cases have an expected recurrence rate of around 20% (7, 8).

An autovaccine can also be used as an adjunct to antibiotic therapy. However, concurrent antibiotic therapy is not recommended in the case of oral (swallow) vaccines. This is because antibiotic treatment may alter the gut microbiota and mucosal immune homeostasis, potentially reducing the effectiveness of the IgA antibody response induced by the autovaccine.

Adverse drug reactions associated with autovaccines are relatively rare. However, redness and swelling at the injection site may occur.
Systemic reactions such as fever, increased respiratory rate, and apathy can also be seen (6).

It should be noted that underlying diseases may influence the effectiveness of the autovaccine.

 

Conclusion

Autovaccines represent an important alternative or adjunct to antibiotic therapy in chronic diseases of companion animals, particularly in the context of increasing antimicrobial resistance.

 

Johannes Kupke, Martina Krapf

 

Services related to this topic:

• Bacteriology (aerobic)
• Oral vaccine
• Injectable vaccine
• Combination vaccine
• Inhalation vaccine

The Laboklin expert panel addresses a wide range of clinically relevant questions. On the topic of feline hyperthyroidism, four endocrinologists and one surgeon came together to share their expertise with us.

The following experts took part in the discussion: Prof. Dr. Felicitas Boretti, Dipl. ACVIM and ECVIM-CA, Head of Endocrinology, Clinic for Small Animal Medicine, Vetsuisse Faculty, University of Zurich; Dr. Katarina Hazuchova, PhD, Dipl. ECVIM-CA, Senior Physician in Internal Medicine, Small Animal Clinic, Giessen; Prof. Dr. Mirja Nolff, Dipl. ECVS, Head of Soft Tissue and Oncological Surgery, Clinic for Small Animal Surgery, Vetsuisse Faculty, University of Zurich; PD Dr. Astrid Wehner, Dipl. ECVIM-CA, Senior Physician in Internal Medicine with a focus on Endocrinology, LMU Munich; PD Dr. Florian Zeugswetter, Head of the Endocrinology Department, University Clinic for Small Animals, Vienna.

Before moving on to diagnostics and therapy, we briefly review the development of feline hyperthyroidism: PD Dr. Zeugswetter explains that the normal feline thyroid gland contains a subpopulation of thyrocytes with a high growth potential. When these are stimulated by certain external factors, hyperplasia occurs. The hyperplastic cells eventually begin to proliferate autonomously, and adenomatous hyperplasia progresses to adenomas and, in rare cases, adenocarcinomas.

The exact triggers of adenomatous hyperplasia are not known. The sharp increase in cases since the disease was first described in 1977 suggests the involvement of environmental factors. Factors as-sociated with the condition in numerous studies in-clude indoor-only housing, canned food, fish-based diets, large fluctuations in dietary iodine, cat litter, and flavonoids (e.g. in soya). Polyphenols (BPA) and polybrominated diphenyl ethers (PBDEs) in food, drinking water, or the environment are also thought to play a role.

PD Dr. Zeugswetter then reviews the most important clinical signs of feline hyperthyroidism.

The main symptoms he mentions are weight loss despite a good appetite, polyuria/polydipsia, scruffy coat, marked restlessness, and increased vocalisation. Gastrointestinal signs such as vomiting and diarrhoea are also common; sometimes diarrhoea may be the only symptom.

This immediately raises the question: which less typical signs should not be overlooked?

Dr. Katarina Hazuchova points out that cats with hyperthyroidism may show pronounced weakness with cervical ventroflexion. Hyperthyroidism should also be considered as a differential diagnosis in cases of polypnoea, as it may reflect increased oxygen demand. Likewise, thyroid function should always be checked in cats with newly developed heart murmurs or other signs of cardiac disease.

The same applies to cats with epileptiform seizures or sudden blindness.

PD Dr. Astrid Wehner emphasises that cardiac changes induced by hyperthyroidism are often not initially clinically relevant and may normalise again once the hyperthyroidism has been successfully treated. Cardiac biomarkers such as (NT-)proBNP or troponin I can be helpful for assessment. If these values do not decrease later on despite well-controlled hyperthyroidism, a cardiological examination should be carried out in order to further classify any underlying heart disease and treat it if necessary.

The laboratory changes that may indicate the presence of hyperthyroidism are discussed by Prof. Dr. Felicitas Boretti. She explains that in cats with elevated liver values and compatible clinical signs, hyperthyroidism should be included in the differential diagnoses. Both ALP (alkaline phosphatase) and ALT may be increased; in practice, ALT is more frequently elevated, although it remains non-specific, whereas an increase in ALP is more typical in the context of hyperthyroidism.

Elevated ALP and phosphate levels in combination with normal renal parameters can be explained by increased activity of bone-specific isoenzymes, reflecting increased bone turnover, and should prompt targeted thyroid diagnostics when clinical findings are compatible.

In most cases, the diagnosis is made based on an increased serum T4 concentration. PD Dr. Florian Zeugswetter addresses the question of how the cat’s age influences the reference interval. In kittens, T4 concentrations are physiologically very high and gradually decrease with age. For cats between approximately 1 and 9 years of age, standard reference ranges are generally appropriate.

In older cats, the reference intervals may, however, be set somewhat lower. Some laboratories have taken this into account by using a lower upper reference limit, as hyperthyroidism is primarily a disease of older cats. When interpreting T4 results, both the cat’s age and the upper reference limit of the respective laboratory should be considered.

This raises the question of how often cats with hyperthyroidism still show a T4 concentration within the reference range. Prof. Dr. Felicitas Boretti points out that this can occur, particularly in the early stages of the disease. If T4 is only mildly increased, natural fluctuations may temporarily bring it back into the reference range, although it is usually in the upper part of the range. Non-thyroidal illness can also lower T4 to the extent that it temporarily falls back within the reference interval.

In cases of unclear findings, PD Dr. Florian Zeugs-wetter recommends repeating the T4 measurement after 2–4 weeks. If there is a strong clinical suspicion of hyperthyroidism but T4 is within the upper reference range, measurement of free T4, endogenous TSH, and reverse T3 can be helpful.

However, the limitations of these parameters must be considered: fT4 may be increased in non-thyroidal illness (NTI), making it relatively non-specific; a TSH concentration within or above the reference range makes hyperthyroidism highly unlikely, but a non-detectable TSH is also common in healthy cats; reverse T3, an inactive metabolite of T4, reliably increases in hyperthyroidism, although further studies are still needed.

If these advanced parameters also fail to clarify the situation, the next step in the diagnostic work-up is the T3 suppression test, or preferably thyroid scintigraphy.

The question is raised as to when a thyroid carcinoma should be suspected instead of benign adenomatous hyperplasia or an adenoma. PD Dr. Astrid Wehner names rapidly growing, solid masses (if not cystic), as well as cats that are difficult to stabilise and require unusually high doses of antithyroid medication, as warning signs. Dr. Katarina Hazuchova adds that these are often patients that have been hyperthyroid for a longer period of time. PD Dr. Florian Zeugswetter also describes palpation findings as indicative: benign nodules tend to be soft and easily movable, whereas firm, poorly movable and larger changes are more suggestive of carcinoma. Scintigraphy is unfortunately less reliable for definitive differentiation than one might expect.

In terms of therapeutic options, the question of prognosis is raised. PD Dr. Astrid Wehner reports encouraging outcomes here. Overall, the prognosis is favourable, although it also depends on the cat’s age and, of course, any comorbidities.

Curative treatment options such as radioiodine therapy are associated with significantly longer life expectancy, lower recurrence rates, and fewer treatment-related side effects. After radioiodine therapy, the median survival time is

approximately 3.7 to 4.0 years. In comparison, the prognosis under medical treatment with antithyroid drugs is less favourable. In a study involving 47 cats treated long-term with thiamazole/methimazole, the median survival time was 2.0 years.

This difference can be explained by several factors. Owners may, over time, no longer be able to consistently administer medication to their cat, or the hyperthyroidism may no longer be adequately controlled medically. With prolonged treatment using antithyroid drugs, resistance may also develop. In addition, adenomatous changes may, over time, progress to carcinoma.

Prof. Dr. Mirja Nolff lists the main indications for thyroidectomy as cats that are difficult to stabilise, in which medication administration is not feasible, those experiencing adverse effects from antithyroid drugs, cats with large nodules, or cases where carcinoma is suspected.

It becomes critical when bilateral surgery is required and the parathyroid glands cannot be preserved.

Reimplantation is not reliably successful, so postoperative hypoparathyroidism must be anticipated. Postoperatively, ionised calcium should be monitored very closely. Another serious but rare complication is laryngeal paralysis.

Prof. Dr. Nolff emphasises that, compared with radioiodine therapy, unilateral thyroidectomy performs less well in achieving euthyroidism. This is because both thyroid lobes are often affected. She therefore recommends informing cat owners that unilateral surgery may not fully resolve the clinical signs. In such cases, removal of the second thyroid lobe may still be necessary if radioiodine therapy is not available. Any resulting hypothyroidism is usually manageable.

The question of whether dietary therapy is an option is addressed by PD Dr. Astrid Wehner. A marked reduction in iodine intake can suppress thyroid hormone production sufficiently to achieve euthyroidism. A specific prescription diet is available. Simply avoiding foods with high iodine

content (fish, seafood) is not sufficient. The time required to achieve euthyroidism varies considerably (28 to 180 days). The diet must be strictly, completely, and permanently adhered to. Unfortunately, this is often the reason for long-term treatment failure. Overall, T4 concentrations may fluctuate and, in some cases, remain elevated.

Antithyroid drugs remain the most commonly used treatment option. Approved veterinary products include carbimazole as a sustained-release formulation and thiamazole (methimazole).

Sustained-release carbimazole can be given once daily according to the manufacturer, while thiamazole preparations are usually administered twice-daily.

Prof. Dr. Felicitas Boretti explains that a trial of once-daily dosing is generally possible. However, in cats with very high initial T4 levels, twice-daily

administration usually leads to faster stabilisation. If T4 levels fall too low at a low total dose, switching to once-daily administration may be appropriate.

Another option is a veterinary-licensed, individually dosed syrup formulation.

Regarding transdermal ointment treatment, PD Dr. Astrid Wehner and PD Dr. Florian Zeugswetter are rather cautious. This formulation has several disadvantages: the active substance, which is teratogenic to unborn children, may come into contact with the owner more easily; absorption is not always consistent; and residual cream in the ear may further affect uptake. In the future, a nanoparticle carrier ointment may become available in Germany, and studies on this are already underway.

PD Dr. Wehner also addresses hyperthyroidism and kidney function. In hyperthyroid cats, there is an increased circulating blood volume and consequently increased renal perfusion. This leads to glomerular hypertension, possibly accompanied by systemic hypertension, which can damage the kidneys and/or contribute to the progression of pre-existing renal disease, as proteinuria may also result. At the same time, glomerular filtration rate increases due to the higher intraglomerular pressure, resulting in lower blood concentrations of renal filtration markers such as creatinine and SDMA.

It is possible that a renal disease only becomes evident after normalisation of thyroid function. The experts agree that in cats that are already azotaemic at the time of diagnosis, treatment with antithyroid drugs should initially be started at a reduced dose. As a rule of thumb, this is about half of the standard dose, or slightly less depending on the severity of the azotaemia, in order to assess the kidneys’ response to therapy.

Radioiodine therapy (RIT) is considered the optimal treatment option. Dr. Katarina Hazuchova explains what needs to be considered when referring a patient. The cost of standard treatment is around €2000 net, and cats usually remain hospitalised for 5–7 days. A cardiological assessment should be performed beforehand; in some centres, full diagnostic work-up including abdominal ultrasound is also required. Antithyroid medication should be discontinued 7 days before treatment, and an iodine-restricted diet 14 days prior. After RIT, cats must remain indoors for four weeks; if pregnant women, breastfeeding mothers, or babies/young children live in the household, they must not come into contact with the cat. Cats that may require intensive care or do not maintain adequate food intake are not suitable candidates for this treatment.

Regarding concurrent renal disease, Dr. Katarina Hazuchova and PD Dr. Florian Zeugswetter are in agreement: if euthyroidism has been achieved

using antithyroid medication and there is no severe azotaemia at that point (creatinine within IRIS stage 2), the cat can be a good candidate for radioiodine therapy. It is very rare for azotaemia to worsen significantly after RIT. However, it is essential to ensure that hypothyroidism does not develop. If azotaemia or clinical signs of hypothyroidism occur alongside low T4 concentrations, levothyroxine supplementation should be initiated.

Monitoring: when should follow-up take place after starting therapy – and what should the final T4 target be? Dr. Katarina Hazuchova recommends the first recheck after 3–4 weeks in stable patients: full blood count, renal parameters, T4, and clinical assessment of symptoms. After another 3–4 weeks, another check is performed; once stabilised, monitoring every 3–4 months is usually sufficient.

Prof. Dr. Felicitas Boretti takes a different approach for cats that are already azotaemic at diagnosis, recommending earlier follow-up after 1–2 weeks.

She also advises measuring TSH to avoid missing iatrogenic hypothyroidism (it should not rise above the reference interval). PD Dr. Florian Zeugswetter defines a different target range for T4 in azotaemic cats: in non-azotaemic cats, the goal is a T4 concentration in the middle of the reference range or slightly below. In azotaemic patients, however, T4 may remain in the upper reference range.

Prof. Dr. Boretti confirms that the timing of blood sampling in relation to tablet administration does not matter. Fluctuations in T4 concentrations during antithyroid therapy are well known, but they do not follow a circadian rhythm and are not related to the timing of medication. However, she emphasises that T4 should be measured in an external, quality-assured laboratory. In-house devices are less reliable and may deviate even within clinically relevant concentration ranges, which can lead to misinterpretation.

The other experts strongly agree with this assessment.

Finally, the topic of side effects is briefly addressed. Dr. Katarina Hazuchova distinguishes between side effects that can often be “waited out” and those that require immediate action. The most common are gastrointestinal side effects – unpleasant for owners, but usually temporary. They should therefore be discussed proactively from the start.

Mild increases in liver enzymes may also occur; these are rare and can normalise despite ongoing therapy. In contrast, severe pruritus and, in particular, blood dyscrasias such as haemolytic anaemia, neutropenia/leukopenia, or thrombocytopenia are critical – in these cases, antithyroid medication must be discontinued.

Such severe adverse effects, PD Dr. Astrid Wehner notes, most often occur within the first month and frequently within the first three months. The choice of oral formulation does not influence their frequency. Dermal preparations, however, may be associated with fewer gastrointestinal side effects.

Prof. Dr. Felicitas Boretti concludes on a reassuring note: even blood count abnormalities are usually reversible after discontinuation of antithyroid drugs. Modern, well-adjustable veterinary preparations allow for optimal control of T4 concentrations, meaning that severe side effects are now seen significantly less often.

Jennifer von Luckner, Ruth Klein

The most common primary nasal diseases are described in more detail below.

 

Space-Occupying Lesions in the Nasal Cavity

Both malignant and non-neoplastic space-occupying lesions can affect the nasal cavity. Regardless of their nature, these lesions may be associated with unilateral or bilateral nasal discharge (ND) of varying character (serous to bloody), stridor, sneezing, and, in cases of larger masses, even skull deformities. All are accompanied by secondary chronic inflammation.

Non-Neoplastic Nasal Masses
Nasal polyps (NP) and hamartomas appear on radiographs as soft-tissue-dense masses, and macroscopic distinction between a non-neoplastic lesion and a benign or malignant neoplasm is not reliably possible.
In cats, nasopharyngeal polyps arising from the pharyngeal region, the auditory tube, or the tympanic bulla have also been described as a separate entity. The exact pathogenesis in both cases remains unclear. Nasal and nasopharyngeal polyps are exophytic proliferations of markedly oedematous and sometimes myxoid fibrovascular stroma, covered by well-differentiated respiratory epithelium (Fig. 1). Individual glands and lymphatic vessels in the stroma are often dilated. They are associated with turbinate destruction, and recurrence is possible.

Nasal Neoplasia
The majority of nasal neoplasms are malignant. Regardless of their histogenesis, they tend to grow relatively slowly, causing significant destruction of anatomical structures and secondary inflammation. Metastases (to regional lymph nodes and the lungs) usually occur late and are often absent at the time of diagnosis. In both dogs and cats, epithelial tumours appear to be more common than non-epithelial tumours, most frequently adenocarcinomas arising from the respiratory, olfactory, or glandular epithelium, as well as transitional cell carcinomas or squamous cell carcinomas.
For non-epithelial tumours, prevalence differs between dogs and cats. In cats, nasal lymphomas, followed by fibrosarcomas, are the most common tumours after carcinomas, whereas in dogs, chondrosarcomas are the most frequent non-epithelial tumours.

 

Infectious Causes of Chronic Nasal Discharge

Bacterial Rhinitis
Chronic bacterial rhinitis in dogs and cats usually occurs secondarily to other nasal diseases.
According to current literature, primary bacterial rhinitis is very rare.

In dogs, Bordetella bronchiseptica has been discussed as a possible primary pathogen. In most cases, chronic rhinitis develops secondarily, with bacteria acting as opportunistic pathogens on nasal mucosa that has already been damaged. The most frequent underlying conditions include idiopathic rhinitis (IR), nasal neoplasms, and nasal mycoses.
Secondary bacterial infections of the nasal mucosa can also occur in the context of oronasal defects, intranasal foreign bodies, and dental pathology.

In cats, damage to the respiratory epithelium following acute infection with feline herpesvirus 1 or calicivirus can lead to chronically recurrent bacterial rhinitis.
Bacterial culture with identification of the causative agent and antimicrobial susceptibility testing is recommended in chronic and chronically recurrent cases.

Nasal Mycoses
Fungal rhinitis in dogs and cats is rare but well-defined, with Aspergillus infections being the most common. Other moulds and yeasts may also be involved.

Unlike other mycoses, in which immunosuppressive mechanisms predispose to fungal infections, nasal mycoses occur in immunocompetent animals.
Canine and feline sinonasal aspergillosis (SNA) is the most common form of fungal rhinitis, with cats being affected less frequently than dogs. It is associated with severe destruction of the conchae and turbinates. Endoscopically, yellow fungal plaques and granulomas can be observed (Fig. 2). In dogs, the frontal sinuses may also be involved. Etiologically, most cases are caused by Aspergillus fumigatus infection.

In cats, an invasive granulomatous form called sino-orbital aspergillosis occurs when the infection spreads from the nasal and sinus cavities into the orbit and surrounding tissues. Clinically, in addition to chronic rhinitis, exophthalmos, orbital pain, and neurological or facial abnormalities may occur.

Another entity caused by yeast infection is nasal or nasopharyngeal cryptococcosis, which occurs in cats and, less commonly, in dogs. In cats, nasal to nasopharyngeal masses without bony destruction are particularly notable, whereas in dogs, turbinate lysis may be observed.

Histology and microbial culture are suitable for distinguishing these conditions and identifying the causative agent. Serological testing is useful for monitoring therapy and disease progression.

 

Chronic Rhinitis of Unknown Cause / Idiopathic Rhinitis (IR)

In addition to nasal neoplasms and sinonasal aspergillosis (SNA), idiopathic rhinitis (IR) is the most common diagnosis in cases of chronic nasal discharge (ND), particularly in dogs. It is a diagnosis of exclusion that requires ruling out all other possible nasal and systemic causes.
IR shows no breed or sex predisposition, although it appears to affect larger, predominantly mesocephalic to normocephalic dog breeds more frequently.

The pathogenesis of IR remains unclear. Various pathogenic mechanisms or aetiological triggers, such as primary and secondary infectious insults, have been discussed. It is suggested that IR may have a multifactorial aetiology and can vary from patient to patient. Investigations have also considered immune-mediated mechanisms and hypersensitivity reactions, showing a partial TH2 immune response, which could indicate a possible allergic basis. However, definitive evidence for allergic rhinitis in dogs, as known in humans, is currently lacking. Literature reports that dogs with IR, even when eosinophils are present in the cytology, typically show only weak and inconsistent responses to antihistamines and glucocorticoids.

Histopathological findings in IR include an inflammatory cell infiltrate dominated by lymphocytes and plasma cells, often accompanied by neutrophils and, less commonly, eosinophils.
In the English-language literature, due to the predominance of lymphocytes and plasma cells, the terms lymphoplasmacytic rhinitis (LPR) or idiopathic lymphoplasmacytic rhinitis are used synonymously. Erosions, ulcerations, bleeding, and turbinate atrophy are also observed in association with IR.

Histopathological changes in IR may occur unilaterally or bilaterally and in varying degrees. However, the inflammatory cell infiltrates are non-specific, and no conclusions regarding aetiology can be drawn. Similar inflammatory and tissue changes can also occur secondary to oronasal defects or dental-related rhinitis.

 

Diagnosis of Chronic Nasal Diseases

The evaluation of chronic nasal diseases is a stepwise process. This includes a clinical examination, imaging, preferably using CT or MRI, rhinoscopy with targeted biopsy, followed by histopathological and/or cytological analysis, and, if indicated, further microbial and mycological culture, serological testing for antigens or antibodies, and/or pathogen detection via PCR.

The following sections provide a detailed overview of the diagnostic steps.

 

Clinical Examination
External inspection may reveal depigmentation of the nasal planum, inflammation of the surrounding skin, crusts, hyperkeratosis, as well as asymmetry or swelling. Other respiratory signs, such as stridor, sneezing or reverse sneezing, may accompany chronic ND.
An oral examination should also be performed to evaluate for dental pathology and inflammation. However, even with a normal oral examination, dental problems, for example oronasal fistulae, cannot be ruled out as a cause at this stage.

 

Imaging
Imaging is essential in the diagnosis of chronic nasal diseases, particularly with CT or MRI. Conventional radiography is limited in its usefulness due to superimposition of bony structures, making evaluation of the skull, turbinates and conchae difficult. Oronasal defects, dental pathology and space-occupying lesions cannot be reliably assessed with plain radiographs.
CT or MRI before endoscopy is recommended because endoscopic examination cannot visualise all areas. Furthermore, secondary lesions may be caused by endoscopy itself, potentially complicating the interpretation of imaging studies conducted after the procedure.

 

Rhinoscopy
Endoscopic examination should be performed both rostrally through the nasal passages and pharyngeally, in a retrograde approach through the choanae. Foreign bodies, debris, or fungal plaques can be visualised and removed. This also allows targeted sampling of the nasal mucosa under direct visual control. Blind biopsies carry the risk of missing relevant lesions and sampling areas that may not be representative.

 

Histopathological and Cytological Examination
For histopathology, it is generally recommended to collect multiple samples from both nasal cavities, even if only unilateral, focal changes are detected. In particular, for space-occupying lesions, a reliable diagnosis is only possible through histopathological examination of appropriate and representative tissue biopsies. Three to four core biopsies of the primary lesion are considered suitable. Insufficient or excessively small tissue samples increase the risk of missing the lesion, which may result in false-negative findings.

In some cases, cytological preparations are suitable for an initial assessment. For nasal mycoses and neoplasms, cytological smears from representative areas may be sufficient to establish a diagnosis (Fig. 3). However, it should be noted that negative results do not exclude these differential diagnoses. Histological examination is essential for determining tumour type.

 

Further Pathogen Diagnostics
In selected cases, bacteriological and mycological testing is indicated. Further information on the individual tests can be found in the current Laboklin Compendium.

 

Conclusion

Chronic nasal discharge (ND) is a clinically significant symptom and encompasses a wide range of differential diagnoses. A thorough, stepwise diagnostic approach is therefore required.

 

Dr. med. vet. Sandra Franke

 

Our services on this topic:

• Histology
• Histology with extended processing
• Cytology
• Cytology with extended processing
• Bacteriology and mycology

For cytological examination, a smear should always be prepared directly in the clinic to ensure optimal cell preservation. Depending on the type of effusion, either a direct smear is sufficient (for cell-rich or blood-rich effusions; prepare the smear similarly to a blood smear) or cell concentration is required (for cell-poor effusions; smear with a stop line, sediment smear, or cytocentrifuged preparation).
For an external laboratory, it is essential to indicate whether a cell concentration was performed.
Only with this information can the cell count be accurately assessed, allowing correct classification of the effusion. A cell-rich direct smear has a different significance (e.g., exudate) than a cell-rich centrifugate (which may indicate a transudate). If samples are being prepared for shipment to an external laboratory, it is also important to include the preliminary report.
Relevant information are the signalment, clinical course, previous diagnostics, prior treatments, and the macroscopic appearance of the effusion if the fluid itself is not being sent.

 

Effusion Analysis – Macroscopic Findings

The assessment of colour and turbidity of the effusion can already provide useful informations (Table 1). However, the underlying cause of the effusion is generally not identifiable macroscopically.

 

Table 1: Broad classification of effusions based on macroscopic appearance

Diagnosis	Colour	Consistency
Hydrothorax / hydroabdomen / hydropericardium	clear	watery
Haemothorax / haemabdomen / haemopericardium	red	watery or coagulated
Serous inflammation	clear	watery, gelatinous
Fibrinous inflammation / chylous effusion	milky	watery, with flakes
Purulent inflammation	brownish	watery, creamy

 

 

It is particularly important that macroscopic assessment is performed immediately at the time of collection. In cases of blood admixture, an iatrogenic process is more likely if initially clear fluid is aspirated that later becomes reddish. In contrast, with haemorrhagic effusions, the fluid is red from the beginning.

 

Basic Parameters

The initial classification of effusions is based on protein concentration and cell count (Table 2).
If total protein measurement is not possible in the clinic, specific gravity can alternatively be determined using a refractometer. The total nucleated cell count (TNCC) can be measured either automatically using a haematology analyser with appropriate settings or manually using a haemocytometer. A semi-quantitative estimate is also possible from a smear during cytological examination (cell count per field × objective² = cells/ml). In specific cases, automated measurement should be avoided, for example, when a septic effusion is suspected (risk of contamination) or when the effusion is highly viscous or flocculent (risk of clotting). Using these parameters, effusions are classified as low-protein transudates, high-protein transudates, or exudates. In veterinary medicine, the term “modified transudate” is commonly used as a synonym for high-protein transudate. However, as it generally does not represent a modification during effusion formation, this term is increasingly avoided in more recent literature.

 

Table 2: Basic classification of effusions based on clinical-chemical parameters

	Cell Count (µl)	Protein (g/l)	Specific Gravity (g/l)
Low-protein transudate	< 1.500	< 25	< 1018
High-protein transudate	1.000–7.000	25–75	1018–1025
Exudate	> 5.000	> 30	> 1025

 

The classification described above is, however, very general and cannot reflect the full range of effusions and their underlying pathogenesis.
Further testing is often required. To differentiate between transudates and exudates, the simplified Light’s criteria can also be applied. An effusion is considered an exudate if the lactate dehydrogenase (LDH) concentration in the fluid exceeds two-thirds of the upper reference interval and the total protein in serum is greater than 4.0 g/dl. Classification using C-reactive protein (CRP, a major acute-phase protein) has also been described. The cut-off value in this case is 4 μg/ml. If this value is exceeded, the effusion is considered an exudate.

 

Specialised Investigations

For specific effusions, additional parameters are available (Table 3). In the case of a blood-rich, it is important to determine whether the blood was introduced iatrogenically during sampling or is originally present in the effusion. A haematocrit value of >3 % is considered indicative of a significant blood component.

The effusion haematocrit should be compared with the current peripheral blood haematocrit.
Haemorrhagic effusions can occur, for example, due to trauma, ruptured tumours (such as haemangiosarcoma), or coagulopathies (e.g., rodenticide poisoning).

For septic effusions, glucose and lactate can be assessed. Both parameters must be measured promptly after sample collection to avoid distortion of results. Glucose decreases due to consumption by cells or bacteria, while lactate increases as a product of anaerobic glycolysis. The differences between serum and effusion values are then calculated. Findings above the corresponding cut-offs (>20 mg/dl glucose, < -2 mmol/l lactate) suggest a septic effusion. Likewise, a lactate concentration >2.5 mmol/l is indicative of a septic process. However, neither parameter is specific, and the suspicion should be confirmed with additional tests. Bacteriological examination is also recommended in such cases.

For lymphocyte-rich effusions, triglyceride and cholesterol concentrations can help determine whether a chylous effusion is present. It is best to compare triglyceride concentrations in the effusion and serum (chylous effusion: effusion triglycerides > serum). Very high triglyceride concentrations in the effusion (>100 mg/dl) and a low effusion cholesterol/triglyceride ratio (<1) are also indicative of chylous effusions. It should be noted that lymphocyte-rich effusions are most commonly caused by heart disease (~70 %) rather than neoplasia (~25 %).

If a lymphoma is suspected, lymphocyte clonality can be assessed using PARR or immunophenotyping can be performed by flow cytometry. PARR is well suited to confirm lympho-ma, but a negative result does not rule it out; only a positive result is diagnostic. Immunophenotyping requires good cell preservation, so the sample must not be too old (see also LABOKLIN Aktuell, Issue 11/2024: “Leukaemias in Dogs and Cats”).
Thymidine kinase is a proliferation marker and can provide valuable information, particularly during follow-up, although it has not yet been validated for pleural effusions.

If an uroperitoneum is suspected, creatinine and potassium can be measured and compared in effusion and serum. In cases of suspected bilious effusion, bilirubin can be assessed accordingly.
If pancreatitis is suspected, lipase can be measured in the effusion (Table 3).

In cases of suspected feline infectious peritonitis (FIP), tests in addition to elevated total protein (>45 g/l) include the albumin/globulin ratio (<0.6) and the Rivalta test (positive). Ultimately, detection of the pathogen is recommended, which can be performed using coronavirus PCR from the effusion.

 

Table 3: Parameters for specific diagnostic questions

	Parameter	Cut-off / Result
Haemorrhagic effusion	Haematocrit / PCV	effusion > serum, > 3 % significant
Septic effusion	Glucose   Lactate	serum – effusion = > 20 mg/dl  Serum – Erguss = < -2 mmol/l or Lactate > 2,5 mmol/l
Chylous effusion	Triglycerides     Cholesterol	triglycerides > 100 mg/dl or effusion > serum (3:1) or cholesterol/triglyceride ratio < 1
Lymphoma	Lymphocyte clonality (PARR) Flow cytometry   Thymidinkinase	monoclonal proliferation predominance of a lymphocyte subpopulation (surface markers) proliferation marker (not validated for pleural effusions)
Uroperitoneum	Creatinine Potassium	effusion > serum (2:1) effusion > serum (1,4:1)
Bilious effusion	Bilirubin	effusion > serum (2:1)
Pancreatitis	Lipase	effusion > serum
FIP	Albumin, Globulin Rivalta test Coronavirus-PCR	A/G ratoio < 0,6 Rivalta test positive coronavirus-PCR from effusion or corresponding lesions (tissue) positive

 

 

Cytology

Semi-quantitatively, cytology itself can provide a rough estimate of cell count and protein content, allowing a preliminary classification of the effusion type. However, automated measurements are generally preferred. The main question addressed by cytology is usually which cells are present. In particular, cytology is used to search for tumour cells or intracellular microorganisms. It also allows microscopic differentiation of leukocytes (e.g., increased neutrophils or eosinophils, lymphocytes, macrophages).

If a septic effusion is suspected, cytology is advantageous for several reasons: to estimate the cell count (these samples should not be measured in automated analysers due to contamination or clotting risk), to detect intracellular pathogens (differentiation from secondary contamination), and to assess the morphology of neutrophils (degenerative changes). Cytological detection of filamentous bacteria (e.g., Nocardia spp., Actinomyces spp.) can also be diagnostically significant, as these bacteria require special culture requirements. Additinally, cytology can sometimes provide information on chronicity. For example, in haemorrhagic effusions, erythrophagocytosis can be observed within a few hours, whereas siderophages typically appear after approximately 2–4 days. Both are indicators of red blood cell breakdown. The presence of platelets without signs of red cell degradation suggests an iatrogenic or peracute process.

Certain cytological structures can further indicate the origin of the effusion. In an uroperitoneum, urine crystals may be present; in a bilious effusion, bilirubin crystals or bile can be detected.
Mesothelial cells may be present in any effusion. In chronic effusions / chronic inflammation, these cells can exhibit marked dysplasia, which makes a morphological differentiation of mesothelial and carcinoma cells challenging or in some cases impossible. In neoplastic effusions, it is important to note that the primary tumour does not necessarily reside in the same compartment. Moreover, only a positive cytology result is definitive, as not all neoplasms shed tumour cells into the effusion.

 

Conclusion

With only a few parameters (macroscopic findings, total protein, and cell count), it is generally possible to perform a rough classification of the effusion already and thus narrow down the differential diagnoses. However, additional investigations are often required depending on the suspected diagnosis. This article summarises the most commonly used parameters (see Tables 1–3). Cytological examination provides further specific information and is particularly important for septic and neoplastic effusions. It can also provide valuable information in cases of hemorrhagic effusions, uroperitoneum, and bilious effusions.

If only a small volume of material can be obtained, cytology is always recommended, as it allows at least a semi-quantitative basic classification in addition to the morphological assessment.

 

Dr. Katrin Törner

 

Our Services on This Topic

• Cytology / Cytology Requiring Increased Effort
• Body Cavity Effusion Analysis (Cytology, total protein, cell count, Rivalta test [cat], cholesterol, triglycerides, albumin/globulin ratio)
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