Skin lesions on head and pruritus in a dog

Maciej Guzera1,2 DVM PhD DipECVCP MRCVS
Agnieszka Cekiera3 DVM PhD
Gerhard Loesenbeck1 Dr. med. vet., Fachtierarzt für Pathologie

1 Laboklin, Bad Kissingen, Germany
2 Laboklin Polska, Warsaw, Poland
3 Wrocław University of Environmental and Life Sciences, Wrocław, Poland


SIGNALMENT
Dog, 10 years old, female entire, Yorkshire Terrier.

HISTORY
A dog was referred to a veterinary dermatologist with a 2 year history of waxing and waning skin lesions on the head and pruritus affecting the face and ears. Worsening of the skin condition was observed by the owner during the last 4 months – pruritus became more severe and generalized. The dog also had a history of conjunctivitis and otitis. Histopathological examination performed few months earlier indicated the presence of chronic folliculitis and furunculosis. The dog was fed commercial dry and wet food. She was not in contact with other animals and had no travel history. Previous treatment included systemic antibiotics, antiparasitic and non-steroidal anti-inflammatory drugs (tolfenamic acid), topical polyvalent otologic and ophthalmic preparations, shampoo therapy, saline compresses and a dietary supplement containing essential fatty acids, zinc and vitamins. The patient also had a trial of glucocorticoid therapy. The dog has been on cephalexin for the last days. Improvement was not observed despite a broad therapeutic approach.

PHYSICAL EXAMINATION
The presence of skin lesions was confirmed on clinical examination (Fig. 1A-C). Coarse crusts were identified on both pinnae and the right cheek. Individualized lesions were also diffusely spread over the back of the animal. Ulceration and marked purulent exudates were evident under the crusts. There was also evidence of conjunctivitis. Skin scrapings were negative for parasites. Other clinical signs were not observed.

Figure 1. Purulent and crusting lesion in the periauricular area (A and B) and conjunctivitis (C) in a dog.

INVESTIGATION
Haematology and biochemistry
Complete blood count and biochemistry were done and were unremarkable.

Cytology
Acetate tape preparations and impression smears from the skin lesions were performed. The cytological picture was similar on both preparations (Fig. 2A-C).

Figure 2. Impression smear cytology from the skin lesion from a dog; 20x objective (A); 50x objective (B); 100x objective (C) (Hemacolor stain).

INTERPRETATION OF RESULTS

Cytology
Cytology showed high numbers of neutrophils (both nondegenerated and degenerated) and macrophages. Some of the macrophages exhibited leukophagia and were phagocytosing small particles and debris. Occasional lymphocytes (mostly small) were observed. Occasional intracellular bacteria (cocci) were also identified. These findings indicated the presence of mixed inflammation with a bacterial component. Infection could have been primary or secondary to another disorder.

Microbiology
Bacterial culture was likely falsely negative given the cytological findings. Antibiotic therapy decreases the sensitivity of culture in detecting bacterial organisms. While submitting a sample for microbiological examination it is important to indicate on the submission that the patient is receiving antibiotics. Negative fungal culture was not supportive of dermatophyte infection.

Thyroid function
Decreased total T4 with normal TSH and free T4 was most consistent with euthyroid sick syndrome, e.g. secondary to skin disease.

CONCLUSION, DIFFERENTIAL DIAGNOSES AND NEXT STEPS
Based on the clinical and laboratory data deep pyoderma was diagnosed. The condition was likely secondary to an underlying disease process, such as allergic disorder or immune-mediated condition. Fungal infection and neoplasia (e.g. lymphoma) were considered unlikely given the previous and current laboratory findings. There was no evidence of hypothyroidism or parasitic disease.
Further diagnostic work-up (i.e. repeated skin biopsy) was planned after controlling deep pyoderma. Antibiotic was changed to doxycycline. Short-term treatment also included polyvalent ophthalmic ointment and saline compresses. At the appointment 2 weeks later no improvement was observed. The lesions appeared also on the forehead, the bases of the pinnae and in the periocular area.
At that point, a decision was made to repeat histological examination. As an immune-mediated process was suspected, treatment with prednisolone (5 mg/kg p.o.) was started immediately after collection of the biopsy specimens. After the initiation of glucocorticoid therapy, the lesions spread all over the body (Fig. 3). The general condition of the dog also worsened – she became slightly lethargic and her appetite and thirst decreased.

FURTHER TESTS

Histology
Punch biopsy was taken from the skin in the periauricular area. Histological examination revealed a severe, nodular, pyogranulomatous and perifollicular inflammation with multifocal furunculosis. Fungal elements (spores and hyphae) were identified on routinely stained section – haematoxylin and eosin (H&E). Their presence was confirmed by Periodic acid–Schiff (PAS) staining. Histological findings were consistent with superficial fungal infection of the skin – dermatophytosis (Fig. 4A and B).

Figure 4. Dermatophytosis in haired skin from a dog: fungal spores and hyphae around hair shafts in ruptured hair follicles and furunculosis; 20x objective, haematoxylin and eosin (H&E) stain (A); 40x objective, Periodic acid–Schiff (PAS) stain (B).

TREATMENT AND FOLLOW-UP

Systemic antifungal therapy was required – a minimum of 6 weeks treatment with itraconazole was initiated. Shampoo therapy and dietary supplementation of β-glucans (for its immunostimulatory properties) were also recommended. Eye preparation and saline compresses were continued. The general condition of the patient improved rapidly after the start of the treatment. On 1 month follow-up the owner reported that the dog was doing very well and marked improvement of the skin condition was observed on clinical examination (Fig. 5). Interestingly, few weeks later owners of the patient were diagnosed with fungal infection of the skin which raised concerns about cross-infections.