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Malassezia (Yeast) Dermatitis
Background
Malassezia dermatitis and otitis occurs most commonly in animals with allergies, endocrinopathies (hypothyroidism, Cushing’s disease), immunosuppressive diseases and other skin diseases. The most common causative organism is Malassezia pachydermatis. It is normal to find a small number of these organisms on cats, dogs and even people. However, overpopulation is common when the normal skin barrier is compromised.
Dogs of any age, breed, or gender can be affected by yeast dermatitis. Predisposing skin factors for Malassezia include warmth, moisture, increased humidity, exaggerated skin folds, obesity and inflamed skin or ears. Commonly affected breeds include West Highland White Terriers, Basset Hounds, Cocker Spaniels, Springer Spaniels, and Chinese Shar Peis. Other conditions that can be associated with secondary yeast infections include endocrinopathies (hypothyroidism, hyperadrenocorticism) and immunosuppression (neoplasia, animals on chemotherapy). Although less common than in dogs, yeast dermatitis can occur in cats, especially in Persian cats or cats with underlying internal disease. Malassezia is not considered to be contagious to other animals or people; however there are very rare reports of immunocompromised humans being at greater risk of infection.
Clinical Signs
Yeast infections can be localized (ears, perianal region, facial skin folds, interdigital spaces) or have a more generalized presentation. Affected animals are often pruritic and may be found licking and chewing the affected sites. The degree of itching does not always correlate with the actual severity of the infection. Some animals have fewer numbers of yeast organisms present but suffer from a hypersensitivity to these organisms. The skin of affected animals is usually erythematous, may have yellow crusting and scaling, and can become hyperpigmented and lichenified over time. Areas of the body commonly affected in dogs include the feet, nails, underside of the neck, axillae, abdomen, legs and under the tail. In cats, yeast infections can involve the chin or face, nails, or occasionally elsewhere on the body.
Diagnosis
Malassezia is usually diagnosed by performing skin or ear cytology. Samples are taken by pressing a slide against the skin, using cotton swabs or acetate tape, or performing dry skin scrapings with a blade. After staining with Diff-Quik, the slide can be examined under the microscope at 1000x (under oil). A few yeast organisms (1-2 yeast organisms per microscopic field) found on the skin or ear are usually considered normal. However, a larger number of organisms in combination with erythema, irritation and pruritus is considered abnormal. Additionally, identification and treatment of the underlying cause of the yeast infection is very important, and other diagnostics may include trial therapy for scabies mites, a hypoallergenic diet trial, allergy testing, bloodwork for hormonal diseases, or skin biopsies.
Treatment
The treatment for Malassezia dermatitis usually involves topical therapy with antifungal shampoos, sprays, wipes and lotions and/or systemic treatments with ketoconazole, fluconazole, itraconazole or terbinafine. The use of topical products alone may be adequate for treating mild or localized infections. Oral medications are recommended for more severe or generalized infections. Some infections require long term therapy for the best results. Occasionally, pulse therapy (therapy used only certain days of the week) is necessary to treat patients with chronic yeast infections. Most animals will also require oral antibiotics for concurrent bacterial skin infections. Treatment of the underlying cause is also very important and may involve trial therapy for parasites, a hypoallergenic diet, allergy hyposensitization injections based on allergy testing, or therapy for any underlying hormonal or internal disease.
Prognosis
The prognosis for yeast dermatitis is good, as long as the underlying cause is identified and treated. Some animals are not cured, but controlled with intermittent topical or systemic anti-yeast therapy.
Judy Seltzer, BVetMed, MRCVS, DACVD
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006
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