Malassezia pachydermatitis is a common yeast organism that is found on normal and abnormal canine skin and ears. On normal healthy skin it causes no problems, but when the environment of the skin is altered for any one of many reasons, Malassezia can cause severe dermatitis or otitis (inflammation of the skin or ears respectively). Some of the factors that can lead to Malassezia dermatitis include moisture (as in dogs with skin folds or floppy ears with narrow ear canals), excessive waxy or scaly build-up (as in seborrhea), and allergic and bacterial skin disease.
Not only is Malassezia a secondary cause of dermatitis in any dog with one of these predisposing conditions, but it may be the primary or initiating cause of skin problems in certain breeds of dogs. This may be related to an alteration in immune response to the yeast.
M. pachydermatitis is also known as M. canis, Pityrosporum pachydermatitis, P. canis.
Malassezia ear and/or skin infections are extremely itchy. The problem may be confined to certain regions - generally the ears, lips, muzzle, inner thighs, or feet - and your dog may chew its feet or scratch in a frenzied manner at the muzzle or ears with its front paws. With ear infection there is often head shaking, pain if the ear is touched, and a waxy discharge. Dogs with more generalized Malassezia dermatitis have reddened, itchy, crusty skin, and are often greasy, scaly and smelly.
Malassezia dermatitis often starts in the summer, corresponding to an increase in humidity and to allergy season, and persists over the winter.
About 50% of dogs with this condition have an underlying problem, especially seborrhea, allergies, or a bacterial skin infection. Dogs with these conditions generally all have greasy, crusty, smelly skin but where there is Malassezia infection, there is also extreme itchiness.
It is essential to sort out whether the Malassezia is the primary problem or is occurring secondary to another condition that can be treated. In either case the yeast infection must be cleared up, and then your veterinarian will look for an underlying cause. If none can be found, and the yeast infection quickly recurs, this suggests that the Malassezia is the primary problem.
This condition is treated with anti-fungal drugs and medicated shampoos. The itchiness usually subsides within a week, and the skin lesions within a few more weeks. Your dog must continue taking the drug for another week or so beyond that.
Commonly there is recurrence of the yeast infection, although the frequency may be reduced if an underlying cause can be identified and treated or managed. Sometimes maintenance treatment is required to prevent frequent yeast infections. This may involve weekly medicated baths and your dog taking antifungal drugs once or twice a week. Your veterinarian will work with you to determine how your dog's skin condition can best be kept under control.
There are many differential diagnoses for this condition and most of them can also be associated with or can trigger Malassezia infection. This can make diagnosis perplexing. Malassezia-associated dermatitis should be considered in any persistent scaly, seborrheic, pruritic dermatitis where other differentials have been ruled out and there is a lack of response to treatment.
Cytologic examination is a useful and readily available diagnostic tool. Samples are collected by vigorous rubbing of a cotton swab on affected skin, superficial skin scrapings or pressing a slide onto the skin. These samples should be heat-fixed, stained (NMB or Diff-Quik), and examined for numerous round or oval, budding yeastlike cells.
Skin biopsies may also demonstrate the presence of the yeast. Culture is not a reliable way to identify a Malassezia infection.
Although little is known about the inheritance of this condition, it is preferable not to use dogs with severe or recurring yeast infections for breeding.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
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.
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