Group 1 (Discontinuation after the Starter Set): This group included dogs in which ASIT was discontinued after the initial treatment. Out of 2208 initial treatments, no follow-up treatments were ordered for 930 (42.1%).

Group 2 (Discontinuation after at least one follow-up treatment): This group included dogs in which ASIT was discontinued during the maintenance phase. In 1230 of 3662 ASIT follow-up treatments ordered (33.6%), no further follow-up treatments were ordered.

To determine the reasons for ASIT discontinuation, the treating veterinarians were contacted by telephone or via written questionnaires.
Several possible reasons could be selected by the veterinarians. The collected data was analysed descriptively and statistically.

Reasons for ASIT Discontinuation:

Cancellation after the starter set (group 1, fig. 1):

A total of 247 responses with 259 reasons for not receiving follow-up treatment after the initial treatment were analysed. Patients (n = 9) for whom no further ASIT was ordered due to death were not included in the analysis. The three most common reasons were lack of owner compliance/loss of contact (36.7%), insufficient/no improvement (21.6%), and discontinuation due to good treatment success (10.4%).

Cancellation after at least one follow-up treatment (Group 2, Fig. 2):

A total of 310 responses with 342 reasons given for why no further follow-up treatment took place were analysed. The average duration of ASIT treatment was 2.4 years. Patients (n = 42) for whom no further ASIT was ordered due to death were not included in the analysis. The three most common reasons for discontinuation of ASIT were lack of owner compliance/loss of contact (30.4%), insufficient/no improvement (23.7%), and discontinuation due to good treatment success (19%).

How Can ASIT Discontinuations Be Reduced and  the Success of ASIT Treatment Optimised?

Initial treatments usually last for six months, which is significantly shorter than the recommended 12 months required to evaluate success. It can take up to a year for the maximum benefit of ASIT to become clinically apparent. In over 40% of the initial treatments in this Laboklin study, no follow-up treatments were ordered, and ASIT was therefore discontinued prematurely after the initial treatment.

If ASIT is successful after one year of therapy, it should be continued for life. Among the dogs examined during the maintenance phase, ASIT was discontinued in approximately 34% of cases.

Lack of owner compliance/loss of contact

The most common cause (about 37% in Group 1 and about 30% in Group 2) was a lack of owner compliance and/or a loss of contact between the veterinarian and the owner.

Owner compliance (Co-operation of the owner in implementing the recommended therapeutic measures) is a decisive factor for the success of the therapy. Owners should be educated in detail about the therapy protocol, the duration of therapy, the delayed onset of ASIT’s action, and the expected costs to optimise their expectations. A key factor here is continuous communication, especially during the first year of therapy.

In a study by Fennis et al. (2022), dogs that were regularly presented for veterinary check-ups in the first year of therapy showed a significantly higher success rate than those that were not monitored by a veterinarian. Regular check-ups not only ensure communication but also allow for continuous patient monitoring, enabling the diagnosis of secondary infections and adjustments to the protocol.

With accelerated and simplified initiation protocols (e.g., rush or cluster protocols and intralymphatic immunotherapy), the maintenance dose is reached more quickly. This approach could reduce the delay in effect and the time until success becomes clinically visible, thereby increasing owner compliance.

Another benefit of such initiation protocols is that ASIT injections are administered exclusively by the veterinarian, ensuring that patients remain under continuous veterinary supervision during the first months of therapy.

Less success than expected

The second most common reason for discontinuation in both groups was insufficient treatment success (approximately 22% in group 1 and approximately 24% in group 2). This was often mentioned in combination with poor owner compliance. The success of therapy should be assessed no earlier than after one year, which highlights an educational issue when ASIT is discontinued prematurely due to perceived lack of success after the initial treatment. These dogs were declared non-responders too early. The delayed onset of ASIT’s action should be clearly communicated by the veterinarian to manage owners’ expectations and reduce premature discontinuation within the first year of therapy, ultimately leading to higher ASIT success rates.

Anti-pruritic symptomatic therapies are often required during the initial months of ASIT to rapidly alleviate clinical signs until ASIT’s effects take hold. This is another factor that can improve owner compliance. However, the duration and dosage of such medications should be kept as low as possible. Pruritis should be reduced but not entirely eliminated, as completely suppressing pruritis can obscure the need for protocol adjustments.

Success rates of ASIT after at least one year of therapy are reported in the literature to be as high as 80% in dogs with CAD, aligning with the findings of this study (approximately 24% of cases in the maintenance phase were discontinued due to lack of success). It is generally expected that maximum treatment success will be apparent within the first year of therapy. If no clinical improvement is observed after one year and additional symptomatic therapies cannot be significantly reduced, the animal is classified as a non-responder, and ASIT is discontinued, as further response to therapy is unlikely.

Defining success correctly is crucial: ASIT is considered successful if the treated dogs exhibit more than a 50% improvement in clinical symptoms or if the need for additional symptomatic medication is reduced by more than 50%. CAD typically requires a multimodal treatment approach – a combination of several treatment options – to achieve optimal management.
In addition to consistent ectoparasitic prophylaxis, dogs experiencing acute allergic flare-ups should always be examined for secondary infections.
Acute flare-ups may necessitate short-term symptomatic therapies.

To further reduce the risk of ASIT failure, combination therapy should be considered, such as essential fatty acids, moisturising shampoos (to improve the skin barrier), and topical hydrocortisone products.

Before a dog is classified as a treatment failure, it should be carefully evaluated to determine whether there has truly been no improvement (e.g., using an itch scale, accurately recording the frequency of allergy flare-ups, and assessing the duration and dosage of additional symptomatic therapies).
Some respondents noted that ASIT was discontinued due to insufficient effectiveness, but that a deterioration in the condition occurred after discontinuation.

Another measure to optimise treatment success is the individual adaptation of the protocol, particularly with regard to the injection quantity and/or treatment intervals.

Furthermore, the lack of treatment efficacy in some patients could be explained by the presence of other pruritic conditions (e.g., food allergies or ectoparasites) that were not ruled out before starting ASIT. CAD is a diagnosis of exclusion, which should only be made after ruling out potential differential diagnoses and before initiating ASIT

Cancellation in case of successful response

The third most common reason for discontinuing ASIT in both groups was that the dogs had improved under treatment, leading to discontinuation of ASIT (approx. 10% in group 1 and 19% in group 2). Most patients require lifelong therapy to permanently manage CAD.
There is limited published data on the long-term effects of ASIT in dogs after therapy discontinuation. The few uncontrolled studies available indicate that most dogs deteriorate once ASIT is stopped.

This was also reported several times during the course of this study. Experience has shown that restarting ASIT can be complicated; allergy tests are often necessary, initial treatment must be restarted, and some dogs no longer respond as effectively.
It is therefore generally recommended not to interrupt ASIT if it is successful.
However, an individual attempt can be made to extend the injection intervals, as noted by 8.5% of respondents in group 2. If treatment success remains stable over several years during the maintenance phase, injection intervals can be gradually extended to up to 8 weeks.

Side effects

In approximately 6% of cases in group 1, ASIT was discontinued due to side effects.
The most common side effect of ASIT during the induction phase is increased pruritis after the injections, which also corresponds with the findings of the present study. If increased pruritis occurs immediately after the injection, the amount of allergen extract should be reduced, and the initiation protocol should be customised.
Owners should closely monitor their dogs’ reactions to the injections and provide immediate feedback to the treating veterinarian, so the ASIT protocol can be adjusted in the event of adverse reactions.
The Laboklin team is happy to assist with any questions regarding protocol adjustments.

Costs

In this study, costs were the reason for ASIT discontinuation in approximately 7% of group 1 and approximately 4% of group 2. For owners, the costs of ASIT in the first year, including the allergy test and regular veterinary check-ups, may appear high.
However, from an economic perspective, ASIT is much more cost-effective in the long term than purely symptomatic therapy. Poorly controlled allergy sufferers require more frequent veterinary visits, higher quantities of anti-pruritic medication, and more frequent treatment for secondary infections, as well as therapeutic measures for the potential side effects of symptomatic medication. This information can also help motivate owners to continue ASIT for the entire first year of treatment, or even into the second year of maintenance therapy, even if the therapy is moderately successful.

Conclusion

To summarise, ASIT is an essential component of the multimodal therapy management of CAD and a lifelong form of treatment that requires strong co-operation between owners and veterinarians.
The first year of therapy demands close monitoring of the patients and is the critical period for the success of the treatment.
The most common reasons for ASIT discontinuation are a lack of owner compliance or loss of contact with owners, as well as overly high expectations of success. Improved education and communication, regular check-ups, and strict adherence to ASIT guidelines can increase the number of dogs that successfully respond to and benefit from ASIT.

Dr. Elisabeth Reinbacher

Range of Services – serological allergy tests

Intracutaneous Allergy Tests
Allergen-Specific Immunotherapy

Therefore, a pathohistological examination should always be carried out to confirm the diagnosis. In this case, the optimal material for examination is a pustule, which should ideally be removed in toto using a punch biopsy (ideally 6–8 mm). If no pustules are found in the classic locations, the next best option is to take samples from the area of thick crusts, under which acantholytic cells are usually present. If the crust detaches from the skin punch during sampling, it should definitely be placed in the sample container as well. Shaving and disinfection before the biopsy should be avoided if pemphigus foliaceus (PF) is suspected, as these procedures can damage the delicate pustules.
In the presence of secondary infection or advanced disease, clinical symptoms may be obscured, making diagnosis more difficult, with this autoimmune disease often not being included in the differential diagnoses. In such cases, cytology often shows only isolated or no acantholytic cells, in addition to inflammatory cells and microorganisms, and pathohistology may also not provide a clear result. One reason for the development of these complicated cases may be inconsistent pretreatment with antibiotics and immunosuppressive drugs when a definitive diagnosis was not made before the use of these medications. If cytological examination in these complex patients only indicates secondary infection, appropriate treatment for the bacteria or Malassezia should always be performed before obtaining samples for pathohistology. In cats, Malassezia dermatitis is almost never due to allergy alone, as it is in dogs; rather, Malassezia in this species usually indicates a more serious underlying disease process.

Therapy

The treatment of pemphigus foliaceus (PF) is based on the use of immunosuppressive drugs, either as monotherapy or, more commonly, in combination with different agents. Glucocorticoids are usually employed as the first-line treatment.
High doses are typically required in the early stages, with dexamethasone sometimes proving more effective for cats. The aim of the treatment is to achieve remission or at least a significant improvement in symptoms as quickly as possible, initially with high doses, and then to reduce the dose to the lowest level at which the patient can be kept under control (“hit hard, then back off”) to avoid side effects. If glucocorticoid monotherapy is insufficient to halt the progression of skin lesions, combination therapies with azathioprine (not for cats!), cyclophosphamide, chlorambucil, and mycophenolate mofetil are viable options.
Depending on the study, cyclosporin shows varying success rates and frequent side effects; the off-label use of oclacitinib has also demonstrated varying degrees of success in the treatment of dogs and cats with PF in case reports and pilot studies.
Topical preparations containing tacrolimus or glucocorticoids, such as hydrocortisone aceponate, can be used in combination with systemic therapy and sometimes even as monotherapy.

Prognosis

The prognosis for patients with pemphigus foliaceus (PF) varies greatly depending on the study; however, in general, cats have a much better prognosis (90% remission) than dogs. More recent studies indicate that treatment for dogs is also successful: 52% of dogs achieved complete remission, 35% partial remission, and only 13% were euthanised. The reasons for euthanasia in these 13% of patients included no response to treatment in only 36% of cases, unacceptable side effects in 18%, and pemphigus-unrelated or unknown circumstances in 46%. The average duration of remission in dogs is reported very differently: Almela and Chan (2021) report 4 to 7 weeks, while Mueller et al. (2006) report 7 to 12 months, depending on the treatment protocol. In cats, remission usually occurs within a month. In most patients, immunosuppressive therapy must be continued for life, as relapses are very common after complete withdrawal of the drugs. However, in studies, 2% and 12% of dogs, as well as 17% of cats, were reported to be without any relapse during the observation period after withdrawal of all medications.

Conclusion

Pemphigus foliaceus is the most commonly diagnosed autoimmune skin disease in dogs and cats. Cytology can help exclude differential diagnoses and confirm the clinical suspicion of PF; the final diagnosis is made through the pathohistological examination of punch biopsies. Immunosuppressive medications, often in combination with several drugs, are used therapeutically. Most patients respond well to the therapy, but it may take some time to achieve complete remission.

Dr Maria Christian

Laboratory Services Relating to the Topic:

• Cytology
• Pathohistology

Table 1: Consensus definition of severe blistering skin reactions (human medicine)

Criteria	EM minor	EM major	SJS/TEN overlap	TEN with maculae	TEN without maculae
Skin detachment	<10%	<10%	10-30%	>30%	>10%
Target lesions	typical or atypical	atypical	atypical	atypical	atypical
Raised lesions	yes	no	no	no	no
Distribution	primarily on trunk	primarily on limbs	primarily on limbs	primarily on limbs	primarily on limbs
Progression to TEN	no	possible	possible/likely	–	–

 

Table 2: Scoring system by type of score (human medicine)

Criteria	Points
Age >40	1
Heart rate >120	1
Underlying malignant tumour disease	1
Skin detachment >10% on the first day	1
Urea >10 mmol/L	1
Bicarbonate <20 mmol/L	1
Serum glucose >14 mmol/l	1
Scorten score	Risk of mortality
0-1	3,2%
2	12,1%
4	35,8%
4	58,3%
>4	>90%

 

EM for cats and dogs

EM is a rare skin disease that affects 0.4% of canine dermatological patients and 0.11% of feline patients, according to a study conducted at an American university hospital. The incidence of SJS/TEN and TEN remains unknown. In humans, a diagnosis of EM requires evidence of typical or atypical target lesions; however, classic target lesions are observed in only a minority of cases in dogs and cats. EM presents with variable clinical features but is often characterised by bilaterally symmetrical maculopapular eruptions that primarily affect the axilla and groin, as well as the oral mucosa, pinna, and footpads.

These lesions are painful but generally non-pruritic. While EM is strongly associated with herpes simplex virus (HSV) infections in humans, adverse drug reactions appear to be the primary cause in veterinary medicine.
Various medications, including antibiotics (e.g., chloramphenicol, enrofloxacin), antiparasitics (e.g., ivermectin, moxidectin, levamisole), and even shampoos (e.g., benzoyl peroxide), can trigger EM in dogs (see case study Figures 1 and 2). Known infectious triggers include anal sac inflammation, pneumocystis infections, as well as herpes and parvovirus infections. In cats, EM may be associated with feline herpesvirus infection (FHV-1, Figure 3) or adverse drug reactions. Additionally, neoplasia might be an underlying cause, and thymoma-associated exfoliative dermatitis may represent a form of EM in cats. In a significant proportion of cases, no identifiable trigger is found, and the disease is considered idiopathic.

Since target lesions, considered pathognomonic in human medicine, often do not appear in veterinary medicine, diagnosing EM requires a thorough medical history, including previous drug therapy, as well as clinical findings and pathohistological examination.
The pathohistological picture of EM is characterised by transepidermal keratinocyte apoptosis with lymphocytic satellitosis, accompanied by lymphohistiocytic interface dermatitis and ulceration (see Figure 4).

The treatment of diseases within the EM complex depends primarily on the severity and extent of the changes. Mild cases of EM minor can be self-limiting, whereas EM major, SJS/ TEN, and TEN often require intensive supportive therapy. In general, efforts should be made to identify and, if possible, eliminate the trigger, such as discontinuing any medication suspected of causing an adverse reaction. If the trigger can be eliminated, the skin lesions in EM patients resulting from an adverse drug reaction typically heal over several weeks without the need for immunomodulatory therapy. If the cause of EM cannot be identified, or if the severity of the disease warrants it, immunosuppressants such as glucocorticoids, azathioprine, and ciclosporins may be used. Intravenous immunoglobulins (IVIG) are another, albeit cost-intensive, therapy option. However, recent data from human medicine indicate that IVIG has no significant effect on the mortality rate of TEN, at least in adult patients.

The treatment of SJS/TEN overlap and TEN is based on three fundamental principles:

1. Discontinuation of medications suspected to be the trigger or addressing the underlying cause, such as bacterial infections.
2. Correction of fluid and electrolyte imbalances.
3. Prevention of wound infections and sepsis due to skin detachment and ulcers.

Additionally, efforts should be made to minimise the progression of skin detachments through immunomodulatory therapy. This aspect of treatment remains controversial, as such therapy may increase the risk of sepsis. Data from human medicine indicate that ciclosporins can reduce mortality in patients with TEN, likely due to their inhibition of T-cell function via the calcineurin phosphatase pathway.

Diseases of the EM complex present significant diagnostic and therapeutic challenges, where pathohistological examination is crucial for accurate diagnosis. Our clinical and dermatopathological team is available to assist with complex skin cases.

Ines Hoffmann

Since a Chorioptes infestation usually causes itchy changes on the fetlocks, you can also hold a petri dish under the affected area and scrape material into it with a scalpel blade.

The trichogram

For trichoscopy, you need a mosquito clamp, a microscope slide, oil and a microscope. The hairs are pulled out in the direction of the hairline and placed on a microscope slide with a drop of paraffin oil. The samples are covered with a cover slip and analysed with the 4x and 10x magnification.

Trichoscopy can be used to diagnose dermatophytosis, however, this requires a certain amount of skill on the part of the examiner. The infected hair is often covered with spores and interspersed with hyphae. They therefore have an irregular (‘dirty’ looking) surface and are broken off at one end.
However, a fungal culture or PCR is necessary in all cases to determine the type of dermatophyte.

Sometimes hair lice or their nits are also found on the hair.

The trichogram can also be useful in the diagnosis of non-inflammatory alopecia. Malformed roots can be found in follicular dystrophies/dysplasias and alopecia areata.

Fungal examination

This requires a mosquito clamp, small paper bags for transporting the test material and Petri dishes with Sabouraud agar and DTM (Dermatophyte Test Medium) double culture medium.

Fungal culture and PCR

If dermatophytosis is suspected, hair samples should be sent to the laboratory. A fungal culture and/or PCR detection can be carried out in the laboratory. The hair is plucked from the edge of the suspected lesion.

Cytological examination

The cytological examination is one of the most important and most frequently performed examinations in dermatology. It requires: microscope slides with a frosted edge for labelling, hypodermic needles, syringes, cotton swabs, scalpel blades, adhesive strips, staining solution, good quality microscope with 100X immersion magnification and immersion oil.

The cytological examination of samples is a useful, quick and inexpensive method for obtaining important information about an efflorescence within a few minutes. Depending on the skin change and localisation, there are various techniques for obtaining samples.

Fine-needle aspiration

This technique can be used for all types of nodules. In principle, 20 – 25 G hyperdermic needles and 2 – 20 ml syringes can be used. As a general rule, the softer the tissue to be aspirated, the finer the needle should be.

The syringe is inserted into the tissue to be analysed and a vacuum is created. The needle is then retracted beneath the surface of the tissue and additionally reinserted at least twice in different directions in order to aspirate different areas of the lesion. To prevent the aspirated material from the needle from entering the syringe, the vacuum is released while the cannula is still in the tissue. The cannula is removed again, air is aspirated into the syringe, the needle is replaced and the contents of the needle are squeezed out onto the centre of one or more slides. Smearing should take place immediately after removal.

Impression cytology

This technique is used for all exudative lesionss, oily and scaly skin surfaces, pustules and crusts, cut surfaces of skin incisions or excision biopsies after the removed mass has been cut in half. In principle, a slide is ‘slapped’ onto the area from which the sample is to be taken. In the case of a crusty skin change, either the underside of the crust is pressed onto the slide or the crust is removed and the slide is pressed onto the now exposed area under the crust.

Staining techniques

The slides must first be air-dried.
In practice, modified rapid staining according to Wright is most commonly used (e.g. Diff Quik® or Hemacolor®). The slide is immersed in the fixing agent followed by the red and blue staining agents for 5 seconds each. It is then gently rinsed off with tap or distilled water and allowed to air dry. The quality of the staining is sufficient to assess inflammatory exudate and gross neoplastic tissue.

Assesment/Evaluation

First, get an overview with the lowest magnification on the microscope. Then look for an area on the slide where the cells are well stained and lie next to each other. Then go to the high magnification, where the cells and bacteria can be best assessed. The 100 mm objective with oil immersion provides a particularly impressive image.

The skin biopsy

For some skin conditions, a biopsy is the only method of coming to a definitive diagnosis. In principle, the more samples and the larger the samples, the more likely it is that a conclusive result will be obtained. Any secondary infections should be treated prior to the samples being taken, as otherwise no meaningful result can be obtained. It is also very helpful to provide the pathologist with a detailed patient history, as the pathologist is often unable to make a definitive diagnosis without a precise medical history.

In addition to basic surgical instruments, you will need scissors to trim the hair above the lesions, a coloured pencil to mark the lesions to be removed, 2% lidocaine without adrenaline, syringes, biopsy punches with a diameter of 6 and 8 mm, swabs and a container with 4 to 10% formalin. A biopsy is always indicated if lesions have an unusual appearance, no successful treatment has been achieved, the biopsy is the only diagnostic option or a tumour is suspected and a preoperative clarification of the tissue is required.

When taking samples, it is very important to leave the surface layers of the skin untouched.
For this reason, the hair must be trimmed very carefully and the skin must never be pre-treated with surgical disinfectants. The hair is shortened to a length of 0.5 cm using hair scissors. The lesions to be examined must remain intact.

Biopsies are generally taken under local anaesthetic. After the site has been marked, between 0.5 and 1 ml of 2% lidocaine is injected. Distribute the agent evenly in several directions and wait a few minutes.

Several biopsies (at least 3) are then taken using a biopsy punch. The number depends on the diversity of the lesions in order to cover an as representative spectrum of the clinical picture as possible. It should be kept in consideration that fresh changes are much more informative than old ones. The skin surface is stretched between the thumb and index finger and pierced with the punch using a twisting and pressing motion. The punch is then withdrawn, the punch cylinder is held with tweezers at the subcutaneous tissue, lifted up and the biopsy is cut off at the still adhering tissue thread. The tissue cylinder should not be held against the epidermis or dermis with the tweezers, as this can lead to artefacts and make assessment more difficult.

After removal, the biopsies are carefully placed on a piece of gauze to remove any blood that may interfere with histopathological assessment. The tissue biopsy is then placed in the formalin.

The wound edges of the punch are adapted with one or two sutures or left open.

The bacteriological examination

A bacteriological examination is necessary in the case of recurrent pyoderma, pyoderma that is resistant after 4 – 6 weeks of antibiotic therapy, rods found in the cytological examination, non-healing wounds and pyogranulomatous inflammation or if required by law. The skin lesion must not be disinfected before the sample is taken. Areas of skin under a crust are suitable for taking a swab sample. The swab is then placed in the transport medium and stored in the refrigerator until it is removed.

PCR examinations

On the one hand, many infectious agents can be detected by PCR testing, and on the other hand, numerous genetic tests for hereditary diseases or colours can be carried out. The sample material for infection diagnostics depends on the pathogen and the stage of infection; EDTA blood (except in the case of graying) or approx. 20 mane/tail hairs with roots are suitable for genetic tests. You can find our comprehensive range of services on our homepage and in the compendium.

Allergy tests for horses

The diagnosis of allergy should always be a clinical diagnosis based on a thorough medical history and clinical examination. The allergy test only serves to identify the triggering allergens so that they can then be specifically avoided or – in the case of atopic dermatitis, insect hypersensitivity (sweet itch) or allergy-related respiratory diseases (equine asthma) – allergen-specific immunotherapy (ASIT, hyposensitisation) can be carried out. The test result must therefore always be interpreted in conjunction with the clinic and medical history. Glucocorticoid administration can falsify the allergy test resulting in particular false negative results. The discontinuation periods for steroids before an allergy test are generally up to 3 months for sustained-release injections, 6 – 8 weeks for oral prednisolone and 2 – 4 weeks for topical formulations (local ointments, sprays, otics, etc.).

We offer cost-effective step-by-step diagnostics with a preliminary allergy test and the main tests (seasonal and year-round allergens, insects) and also a food allergy test. A brand new addition to our programme is the PAX complete test (environmental allergens and/or feed) for horses, in which allergen extracts and recombinant allergens are tested. For details, please refer to our homepage, the compendium or the allergy order form. Allergen-specific immunotherapy can of course also be obtained directly from us.

Conclusion

Dermatology is detective work or a jigsaw puzzle, you have to collect many ‘clues’ or ‘pieces of the puzzle’ to arrive at a diagnosis. The detailed patient history, the clinical examination of the horse’s skin and the inclusion or exclusion of differential diagnoses through various dermatological examinations ultimately lead to the final diagnosis of the skin disease.

Dr. Regina Wagner