Summary
Malassezia pachydermatitis is the name of a species of yeast that normally lives on the surface of the canine skin. In the presence of allergic skin disease or any other kind of inflammatory skin disorder, this microorganism has a tendency to proliferate abnormally. Waxy, oily, scaly and/or moist skin––including the skin that lines the ear canal––is particularly predisposed.
In 50% of cases, Malassezia infection is a secondary disease process. But in certain breeds, a hypersensitivity to this yeast organism (likely the result of an aberrant immune response) may cause a primary version that has been suspected of having a hereditary predisposition of unknown origin.
Symptoms and Identification
The result of Malassezia overgrowth is a malodorous skin infection that has a tendency to cause extreme itchiness. Scaling, dryness, oiliness and moist skin are common signs that may be the primary or secondary result of the Malassezia organism.
The ears, face, belly, underarms and/or feet are usually most affected. Ear infections with Malassezia will result in head shaking, pain and otic (ear) discharge.
Diagnosis of Malassezia infection is achieved simply via cytology (microscopic evaluation of the cells present on the surface of the affected skin). To differentiate between primary and secondary Malassezia infection, all underlying causes are ruled out. In other words, primary Malassezia dermatitis is a diagnosis arrived at by excluding all other possibilities.
Affected Breeds
These breeds seem to have a higher risk of Malassezia overgrowth and/or hypersensitivity:
Treatment
Treatment consists of topical and systemic therapy with antifungal medications. Frequent shampooing and other topical medication application can be sufficient but many severe cases require oral antifungal drugs.
Treatment of any underlying disease processes is imperative but in primary Malassezia dermatitis cases, drug therapy (whether topical or systemic) is considered the only line of defense.
Veterinary Cost
The cost of treating primary Malassezia dermatitis is relegated to the expense of the drugs and medicated shampoos and/or other treatments required to manage the overgrowth of the organism. The expenses associated with secondary Malassezia dermatitis will vary depending on the inciting cause.
Prevention
Though the genetic origins of this condition are not well understood, it’s generally agreed that dogs diagnosed with primary Malassezia dermatitis should not be bred. Breeding management is the only known mode of prevention.
References
OFA
Scott, D.W., Miller, W.H., Griffin, C.E. 1995. Muller and Kirk's Small Animal Dermatology. pp. 351-357. W.B. Saunders Co., Toronto.