Malassezia Dermatitis

Introduction

Malasseszia Dermatitis is a skin disease associated with the yeast Malassezia pachydermatis. It is common in dogs but rare in cats. The yeast is found on skin and mucosal sites in healthy dogs and cats and under circumstances which remain poorly understood can proliferate and induce skin disease.

Pathogenesis

Malassezia pachydermatis proliferates and liberates enzymes and metabolites which induce cutaneous inflammation. Concurrent skin diseases such as atopic dermatitis and primary defects of keratinisation are recognised in approximately 66% of cases. Some dogs may show hypersensitivity to Malassezia pachydermatis.

Signalment

Basset hounds, Cocker Spaniels and West Highland Terriers are predisposed.

History

Affected dogs usually present with a greasy skin disease often with a characteristic odour and a variable degree of pruritus.

Clinical signs

Malassezia dermatitis can complicate or mimic allergic skin disease and scaling skin disorders. The main clinical signs are erythema and a greasy exudate which may result in matted hair with variable amounts of alopecia and scaling. Hyperpigmentation and lichenification occur in chronic cases. Concurrent erythematous otitis externa with variable ceruminous discharge is common. The degree of pruritus is variable but can be extreme especially on the face in a small number of dogs.

Laboratory tests

The most common method of diagnosis is by microscopic examination of a tape strip revealing an increased number of Malassezia pachydermitis. Clear adhesive tape is applied to the affected area and removed, stained and examined under oil immersion. The yeast can also be cultured on Sabrouraud's dextrose agar at 32-37°C for 3-5 days.

Treatment

Treatment is aimed at reducing the yeast population and treating any underlying skin conditions. The first choice of treatment is an antifungal medicated shampoo containing miconazole and chlorhexidine. Selenium sulphide in combination with enilconazole or ketoconazole can also be used topically but is less effective. The use of systemic antifungal drugs such as ketoconazole can also be considered. The response to treatment should be measured by clinical response and by a reduction in yeast populations in skin lesions upon microscopic examination.

References

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
• Foster, A, and Foll, C. (2003) BSAVA small animal dermatology (second edition) British Small Animal Veterinary Association
• Bond, R, Hendricks, A. (2008) Veterinary Dermatology Integrated BVetMed course notes Department of Veterinary Clinical Sciences and Pathology and Infectious Disease. Royal Veterinary College, University of London.