VETERINARY DERMATOLOGY DERMATOLOGIE VETERINAIRE

/v-Malassezia dermatitis

Michael Charach

Malassezia pachydermatis is a saprophytic yeastcommonly found on normal and abnormal skin of

dogs. Malassezia pachydermatis and staphylococci playa significant role in seborrheic dermatitis. Malassezia der-matitis (MD) is common and should be considered inany case exhibiting erythematous, oily, and pruriticdermatitis (1). Specialty dermatology practices maysee 2 or more cases of MD a week.

Malassezia dermatitis is often the reason for thera-peutic or diagnositc failures. When there is a lack ofresponse to glucocorticoids, antibiotics, antiseborrheicshampoos, insecticides, or miticides, one should considera diagnosis of MD (2). Some atopic patients that havefailed to respond to desensitization have subsequentlybeen diagnosed as having MD and, then, have respondedwell to desensitization after the MD was successfullytreated. The diagnosis of food allergy relies upon theowner's observation of decreased pruritus while thepatient is on an elimination food trial. If the patienthas MD concurrently with the food allergy, the ownerwill not observe any decrease in pruitus until the MD hasbeen successfully treated.

Malassezia organisms can be cultured easily fromnormal dog skin, but cytological demonstration of theorganism from normal skin is much more difficult. Adecrease in the host's defenses or changes in the surfacemicroclimate, such as, excessive sebum, accumulationof moisture, and disruption of the epidermal barrier,may lead to proliferation of Malassezia organisms.Allergic, hormonal, and bacterial skin diseases may bepredisposing factors, as are longterm glucocorticoidadministration and antibiotic administration (2). Onestudy demonstrated that atopic dogs had higher numbersof yeast than did normal dogs, but not as many as dogswith MD. Factors associated with increased prevalenceof higher counts of Malassezia pachydermatis wereseborrheic dermatitis, recent antibiotic treatment, andcertain breeds (3).

Malassezia pachydermatis produces lipases that canliberate fatty acids and zymogen in the yeast cell wall,which activates complement, both actions may con-tribute to cutaneous inflammation (1). Two studieshave suggested that the pathogenesis of MD may berelated to the yeast antigens acting as an allergen and thuscausing an immediate-type hypersensitivity reaction. The1 st study showed that when seborrheic dogs were skin

Figure 1. Malassezia dermatitis on the neck of a basset hound.

tested with M. pachydermatis antigen, 30% of themdemonstrated immediate skin reactions (4). The otherstudy, which also injected M. pachydermatis intrader-mally, showed that the mean immediate skin test reac-tions were greater in atopic dogs with MD than inatopic dogs without MD, which, in tum, were greater thanin normal dogs (5). When dogs with MD are biopsied, thehistology is usually consistent with a hypersensitivity pat-tern (1). Some of this hypersensitivity reaction may bedue to the yeast, while some can be attributed to anunderlying food allergy or atopy.

There are many clinical manifestations of MD. Pruritusof a moderate to severe nature is usually a constantfeature. Erythema, hyperpigmentation, erythroderma,grey to white scales, and waxy or oily seborrhea are allvariable in degree, as is the associated offensive odor.

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Animal Dermatology Clinic of British Columbia, 140-8040Garden City Road, Richmond, British Columbia V6Y 2N9.

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Figure 3. Generalized Malassezia dermatitis in a mixedbreed dog.

Figure 2. Malassezia dermatitis on the leg folds of adachshund.

Regional MD is far more common than the general-ized form. The areas of the body that tend to be moremoist and oily are more prone to MD. The most commonpresentation is pododermatitis involving the interdigi-tal spaces or the area between the pads. It is helpful to askthe owner if the dog actually turns the paw over tochew the undersurface of the paws, rather than justlicking the top. Although many allergy-prone breeds maybe affected, Malassezia pododermatitis is commonlyseen in cocker spaniels and golden retrievers. Othercommon regional areas commonly affected include theneck, perianal (under the tail), face (lips, chin, facialfolds), and leg folds (Figure 1). Paw licking and face rub-bing are often associated with allergies, but MD may alsobe an important contributor. Continual face rubbingwith frenzied fits of nose, chin, or lip scratching may beobserved in conjunction with mild erythema, scale, andminor amounts of alopecia. However, this latter der-matitis may be overlooked, as long hair in the areamay obscure these clinical signs. It is imperative that thehair be clipped and the skin closely examined (6).

Pruritus in the perianal area is often associated withanal sacculitis or allergies. However, dogs that rubtheir back end should be examined for MD under the tail.Dachshunds with "accordion-like" folds of skin ontheir legs are also predisposed to developing MD(Figure 2). Paw sucking may be associated with a darkbrown discharge from swollen nail beds and may indi-cate paronychia due to Malassezia pachydermatis (7).

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Figure 4. Clear cellophane tape pads (Pat-it 3M Maskingand Packaging System Division) are cut into strips, and usedto collect surface skin samples for cytology.

Generalized MD is much less common than regionalMD. Most of the generalized MD cases occur in mediumto small breed dogs, although 1 author reported 2 casesin German shepherds, and I have treated a case in aSamoyed that was secondary to hypothyroidism(Figure 3). In addition to the predisposed breeds listedin Table 1, I would add golden retrievers with MD ofthe paws secondary to atopy to the list of predisposedbreeds in Table 1.A diagnosis ofMD is usually suggested by the history,

clinical signs, and failure of other therapeutic modalities.The most useful and readily available procedure for

312Can Vet J Volume 38, May 1997

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Figure 5. Clear cellophane tape pad strips are used to takeimpression smears for cytological examination.

Table 1. Dog breeds predisposed to Malasseziadermatitis (2)silk terrier Shetland sheepdogAustralian terrier collieMaltese terrier German shepherdJack Russell terrier dachshundWest Highland whiter terrier basset houndchihuahua cocker spanielpoodle springer spaniel

the diagnosis of MD is cytological examination. A sam-ple for this can be collected by rubbing the skin with acotton swab, taking a skin scraping, or making a slideimpression. The slide is heat-fixed and stained withDiff-Quick (Dade Diagnostics, Puerto Rica) or newmethylene blue. Some clinicians have found clear cel-lophane tape to be superior for collecting surface skindebris and scales (8). Packing tape is preferred, as it doesnot curl up as Scotch tape does after immersion instaining solutions. The tape is dipped directly into thestain with no heat fixing, and then viewed at IOOOX.I have found a certain commercial pad of clear cellophanetape (Pat-it, 3M Masking and Packaging SystemDivision, St. Paul, Minnesota, USA) the easiest to use,and it gives excellent results. The tape comes in dimen-sions of 3 /2 in by 6 in and there are 25 sheets to a pad.Each sheet can be cut longitudinally into 3 equal widthsusing a box cutter. The tape fits between toes or padsto facilitate the collection of samples (Figures 4-6).Ironically, 1 of the main purposes of this product isthe removal of pet hair from clothes. The diagnosis ofMD is achieved by demonstrating 1 or 2 yeast per fieldat IOOOx. Generally, the more yeast organisms thatare found, the more confident one is of the diagnosis ofMD (8). When there are low numbers of yeast bodiespresent, the diagnosis of MD may be tentative, in whichcase a trial therapy may be the only way to confirmthe diagnosis. Systemic treatment or intense topicaltherapy should result in a positive response (6).The most effective treatment for MD is systemic

therapy with ketoconazole (Nizoral, Janssen Pharma-ceutica, Mississauga, Ontario), 10 mg/kg body weight(BW), P0, ql2h, for 20 to 30 d (10). Topical therapy isusually applied concurrently. Topical treatments, whenused alone, appear to be less reliable than systemicketoconazole (11). One reason for this may be that top-

Figure 6. Clear cellophane tape is mounted on glass slide, afterbeing stained with Diff-Quick (Dade Diagnostics).

ical therapy requires more rigorous frequent applications,either daily or every other day bathing, to be effective.Some cases may fail to respond to topical therapybecause the yeast is too deep in the hair follicle or thepatient is hypersensitive to the organism, thus requiringa more complete clearing of the organism than the top-ical therapy can achieve alone (4,1 1).

Topical therapy can be divided into 3 categories:Creams, shampoos, and rinses. Creams that have beenused successfully on paws include miconazole (ConofiteCream 2%, Janssen Pharmaceutica), ketoconazole(Nizoral Cream, Janssen Pharmaceutica), and clotri-mazole (Canesten, Miles Canada, Etobicoke, Ontario).Shampoos that have been successful include ketocona-zole (Nizoral Shampoo, Janssen Pharmaceutica)andmiconazole (Dermazole, Allerderm-Virbac, Fort Worth,Texas, USA); (Sebolyse, Dermcare-Vet, Queensland,Australia). Helpful but less effective shampoos includeselenium sulphide (Selsun Blue, Abbot Laboratories,Montreal, Quebec; Sellen Suspension, P.V.U., SanofiSante Animale Canada, Victoriaville, Quebec), chlorhex-idine 4% (Hibitane, Ayerst Laboratories, St. Laurent,Quebec), or chlorhexidine 1% (ChlorhexiDerm, DVM,Miami, Florida, USA). The best rinse is probably enil-coazole (Imaverol, Janssen Pharmaceutica). Other rinsesinclude lime sulfur (LymDyp,