7 Malassezia dermatitis
Malassezia pachydermatis is recognized as one of the major flare factors contributing to pruritus, especially in atopic dogs. Several different Malassezia species have been isolated but, of these, Malassezia pachydermatis, a non-lipid-dependent species, is the most studied in veterinary medicine. Malassezia pachydermatis is considered to be commensal on canine and feline skin, and can cause infections when the microclimate on the skin surface or in the ear is altered, or if the host immune responses are compromised. The lipid-dependent species M. sympodialis and M. globosa have been isolated from cats. The recognition of Malassezia dermatitis and its appropriate treatment was the key to successful management of atopic dermatitis in this case.
In most cases Malassezia dermatitis is associated with an underlying hypersensitivity disorder and the distribution of clinical signs may give an indication of the underlying condition. The relevant history to this case included:
In dogs, the clinical signs of Malassezia dermatitis vary according to the intensity of the infection and the area affected. Infection can cause localized or generalized disease and pruritus is a common presenting sign. In most cases the skin lesions include erythema, scaling, hyperpigmentation, lichenification and crusting. Individual, or several concurrent sites such as ears, lips, muzzle, ventral neck, axillae, ventrum, perianal and feet may be involved. Dark brown waxy exudate in the ear canals or adherent to the nails is suggestive of Malassezia infection. Frequently, peripheral lymphadenopathy is also present.
Malassezia dermatitis is less common in cats. It has been associated with facial dermatitis and with otitis externa secondary to allergic skin disease. Generalized lesions in cats have been associated with immunedysregulation in conditions such as the paraneoplastic syndromes.