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A case study of atopic dermatitis

by
01 July 2009, at 12:00am

THIS case is taken from Dr Tim Nuttall’s dermatology referral service at the Small Animal Teaching Hospital, University of Liverpool. 

The patient (pictured at right) was a five-and-a-half-year-old, male, neutered Labrador. 

Owner’s complaint 

Severe pruritus, poor appetite and weight loss. 

History 

■ Pruritus for the last three years, but much worse in the last 12 months. 

■ Initially diagnosed with atopic dermatitis – negative skin tests and biopsy, and no response to two months of flea control and a homecooked pork and sweet potato diet. 

■ Allergy blood tests positive for house dust mites. 

■ Initially controlled on allergen specific immunotherapy, antihistamines and intermittent steroids. 

■ Has got steadily worse over the last 12 months and requires steroids all the time – these cause depression and severe polyuria/polydipsia though. 

■ Little response to antibiotics, various shampoos and homoeopathy. 

■ On monthly flea control with Frontline Combo (fipronil/smethoprene). 

Clinical examination 

■ See figures. Severe inflammation with erythema, excoriation, alopecia, lichenification, hyperpigmentation, erosions, ulceration, bloody exudate and crusts. 

What are your differential diagnoses?

Atopic dermatitis, cutaneous adverse food reaction, Demodex, Sarcoptes, other ectoparasites (Cheyletiella, lice, etc.), staphylococcal pyoderma, Malassezia dermatitis, dermatophytosis, epitheliotropic lymphoma. 

If the dog is atopic why might he have worsened? 

As above, plus inherent worsening of the atopic dermatitis and/or new allergen sensitisation. 

What tests would you like to perform? 

Hair plucks and skin scrapes – no mites seen. 

Cytology – Malassezia, neutrophils and cocci, and chronic inflammation. Fungal culture – saprophyte on DTM. 

Haematology and biochemistry. 

Biopsy and histopathology. 

Intradermal allergen test or allergen specific serology – positive for house dust and forage mites. 

Food allergen specific serology – positive IgG for chicken, fish, lamb and beef. 

Sarcoptes IgG serology positive. 

No response to trial therapy with selamectin or imidacloprid/moxidectin. 

Owners refused to undertake a second food trial. 

Total T4 – 10.4 (13-52). Free T4 and TSH – 11.3 (7-50) and 0.28 (<0.41). 

What is your diagnosis? 

Atopic dermatitis with secondary deep staphylococcal pyoderma and Malassezia dermatitis. Anaemia, neutrophilia and increased globulins consistent with chronic inflammation and/or infection. 

Sick euthyroid syndrome – no evidence of hypothyroidism or other metabolic/endocrine conditions. 

How would you treat this dog? 

Bactericidal antibiotic to manage the pyoderma. 

Antimicrobial shampoo or systemic itraconazole to manage the Malassezia. Potent systemic antiinflammatory, such as ciclosporin (NB. glucocorticoids limited because of adverse effects). 

Other drugs not potent enough initially, but could be used later for maintenance and/or adjunct therapy. 

These include: 

- High quality diet and/or essential fatty acids to improve barrier function. 

- Hydrocortisone aceponate. 

- Phyopica. - Antihistamines. 

- Allergen avoidance and ASIT unlikely to be of benefit now.