Small Animal Dermatology, 3rd edition

482 DISEASES/DISORDERS

DIFFERENTIAL DIAGNOSIS

 Hypersensitivity dermatitis: canine atopic dermatitis, flea allergy, cutaneous adverse

reaction to food, contact dermatitis.

 Superficial bacterial folliculitis.

 Primary and secondary seborrhea/keratinization disorders.

 Drug reaction.

 Epitheliotropic lymphoma.

 Dermatophytosis.

 Demodicosis.

 Scabies.

DIAGNOSTICS

 Diagnosis is made by demonstrating excessive numbers of the organism on diseased

skin, and by a significant improvement in clinical signs following removal of the yeast.

 Skin cytology:
Direct impression, cotton swab, cellophane tape preparation, or “toothpick” for

claw folds

Stained with modified Wright stain (Diff-Quik®)

Apply stain as a drop directly onto the slide; pass a flame under the slide to

improve stain penetration and visualization

Greasy and/or scaly areas are most likely to produce positive results

Yeast are best visualized at 40×or 100×magnification

Seen as 3–8μm in diameter, round to oval shaped with or without monopolar

budding (described as “peanut” or “footprint” shape) (Figure 32.14)

There is no specific number of yeast organisms defined as abnormal; there is

often overlap between normal and increased numbers based on anatomic loca-

tion; few organisms may incite a hypersensitivity reaction.

 Intradermal skin test reactivity:Malasseziaallergen-specific intradermal testing is a

viable tool in determining immediate type hypersensitivity; should be included in

immunotherapy vaccine (allergen-specific immunotherapy – ASIT).

 IgE serologic testing: enzyme-linked immunosorbent assay forMalasseziaallergen-

specific IgE; substantial agreement between IDST and ELISA forMalasseziaallergen-

specific IgE.

 IDST and ELISA: negative testing does not rule out a pathologic role for this organism;

delayed type hypersensitivity may be clinically relative.

 Fungal culture:
Minimal value sinceMalasseziaspp. are commensal organisms
Contact plates: Sabouraud agar or modified Dixon agar
Press plates onto the affected skin surface
Incubate at 32–37◦C for 3–7 days
Malasseziagrows as distinctive yellow or buff, round, domed colonies (1–

1.5 mm) (Figure 32.15).