Page 1230 - Cote clinical veterinary advisor dogs and cats 4th

Malassezia Dermatitis 615

RISK FACTORS • Follicular casts (keratosebaceous material uncomplicated state or secondary Malassezia
• Excessive sebum production, poor sebum adhered to the proximal hair shaft) may dermatitis is also present is required.
VetBooks.ir (particularly in skin folds), a disrupted • Cats, particularly Devon rexes, may present Initial Database Diseases and Disorders
suggest an underlying keratinization disorder.
quality, cutaneous moisture accumulation
with alopecia, erythema, and greasy exuda-
epidermal surface, and altered host immune
• Skin cytologic exam is performed for every
defenses. These alterations are often the result
of primary underlying diseases (e.g., allergy, tion of the axillae, groin, and paws. In some case with compatible historical/physical
findings.
cats, the only manifestation is otitis externa
endocrinopathy). with dark, waxy secretion. ○ Specimens can be obtained by direct
• Specific predisposing disorders include impressions, acetate tape preparations,
allergic skin disease (e.g., atopic dermatitis, Etiology and Pathophysiology or dry or wet swabs from representative
food allergy, flea allergy, contact allergy), Malassezia spp. yeasts are part of the normal lesions.
endocrinopathies (e.g., iatrogenic or spon- skin microbiota. They become opportunistic ○ Malassezia are ovoid, monopolar budding
taneous hyperadrenocorticism, hypothyroid- invaders when changes occur in the cutane- yeasts that resemble the shape of footprints
ism, hyperthyroidism, diabetes mellitus), ous microclimate (e.g., lipid composition, or peanuts. They are 3-8 microns in
primary or secondary cornification disorders, relative humidity) or defense mechanisms diameter (same size as or slightly smaller
metabolic diseases (e.g., superficial necrolytic (e.g., epidermal barrier dysfunction, immuno- than a red blood cell).
dermatitis, zinc-responsive dermatosis), suppression). After colonization takes place, ○ Yeasts are best visualized using high-
nutritional deficiencies, cutaneous or internal yeasts release proteases and lipases that alter power (40×) or oil immersion (100×)
neoplasia, and in cats, retroviral infections cutaneous homeostasis, allowing continued yeast microscopy.
overgrowth. In some atopic dogs, Malassezia • Multiple skin scrapings to exclude superficial
CONTAGION AND ZOONOSIS may elicit a type 1 cutaneous hypersensitivity and deep ectoparasites
Malassezia yeasts have been transmitted from reaction. • Especially with cats, dermatophyte culture
the contaminated hands of dog-owning health to exclude ringworm
care workers to infants in an intensive care DIAGNOSIS
nursery, causing mycotic sepsis. Malassezia yeast Advanced or Confirmatory Testing
should be considered a potential zoonotic agent, Diagnostic Overview • Biopsy and histopathologic analysis: rarely
especially for immune-incompetent individuals. Malassezia dermatitis should be considered for necessary
any pruritic dog or cat. Confirmation requires ○ Suggestive but nonspecific findings include
GEOGRAPHY AND SEASONALITY typical clinical signs, cytologic demonstration parakeratotic hyperkeratosis, epidermal
Malassezia dermatitis can occur more frequently of yeast, and most importantly, response hyperplasia, superficial perivascular
in humid geographic regions and/or with to antifungal therapy. Underlying primary dermatitis, and possibly eosinophilic
underlying causes that worsen seasonally (e.g., conditions must be identified and corrected. microabscesses with or without the finding
atopic dermatitis). Importantly, Devon rex cats may not have an of yeast organisms.
identifiable predisposing disease. ○ Other histopathologic findings may
Clinical Presentation represent changes associated with the
DISEASE FORMS/SUBTYPES Differential Diagnosis underlying dermatosis.
• Localized dermatitis: involving the face Because Malassezia dermatitis is a secondary • Elimination diet trial to exclude food allergy
(perioral, muzzle, ears), ventral aspect of the complication of an underlying disorder in • Intradermal and/or immunoglobulin E (IgE)
trunk (neck, axillae, inguinal area), perineal most cases, identifying whether the underlying serologic testing if history and clinical find-
region (ventral tail, perianal area), and paw disorder (see Risk Factors above) exists in an ings support atopic dermatitis
(interdigital web and nail fold)
• Generalized dermatitis: involving several
regions, as noted above
HISTORY, CHIEF COMPLAINT
• Intense pruritus: most common complaint
• Rancid offensive odor, an oily coat, alopecia,
redness/erythroderma, lichenification, scaling,
and/or relapsing and remitting dermatitis
unresponsive to antibiotics or antipruritics
are frequently observed.
PHYSICAL EXAM FINDINGS
• Skin lesions reflect existing pruritus and
seborrhea and are not specific to Malassezia
dermatitis.
• Lesional skin may be erythematous, hyper-
pigmented, hyperkeratotic, lichenified, scaly,
greasy or dry, alopecic, saliva stained, and
excoriated. Hyperpigmented lichenification
implies chronicity.
• Intertriginous areas (skin folds) are typically
affected. Occasionally, yellow/orange to slate
gray seborrheic plaques are present in body
folds.
• A brown, waxy discharge may be observed
in the claw folds with extension onto the MALASSEZIA DERMATITIS Malassezia dermatitis in a miniature poodle with alopecia, erythema, and
claws proper, signifying paronychia. lichenification on the ventral neck. (Copyright Dr. Manon Paradis.)

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