Small Animal Dermatology, 3rd edition

CHAPTER 16 CONTACT DERMATITIS 267

 Drug reaction

 Parasite hypersensitivity or infestation

 Insect bites

 Bacterial folliculitis

 Malasseziadermatitis

 Dermatophytosis

 Demodicosis

 Cutaneous lupus erythematosus

 Seborrheic dermatitis

 Solar dermatitis

 Thermal injuries

 Trauma from rough surfaces

DIAGNOSTICS

 Closed-patch testing:
Discontinue corticosteroids and NSAIDs 3–6 weeks before testing
Use materials directly from the environment or a standard patch test kit for

humans applied to the skin under a bandage for 48 hours

After 48 hours, patch test allergens are removed from the skin. The test area

should then remain protected and examined over the next 3–5 days for changes.

 Best diagnostic test: eliminate contact irritant or antigen (minimum 7–14 days); fol-

low with provocative exposure (dechallenge/challenge testing).

 Exudate preps to examine for bacterial or yeast infection.

 Bacterial cultures to define secondary bacterial folliculitis if indicated.

 Clipping a patch of hair in a nonaffected region should result in further development

of a local reaction by facilitating contact with the antigen.

 Skin biopsy:
Submission of samples from early lesions preferable to chronic lesions
Biopsy samples from areas under patch test sites particularly useful
Mainly nonspecific superficial perivascular dermatitis with intraepidermal vesic-

ulation and spongiosis in both ICD and ACD

ICD: epidermal degeneration, polymorphonuclear cell infiltrate with leukocyte

exocytosis

ACD: lymphocytic spongiotic or eosinophilic and lymphocytic spongiotic infil-

trate progressing to vesiculation; intraepidermal neutrophilic or eosinophilic

pustules.

THERAPEUTICS

 Eliminate or avoid offending substance(s).

 Bathe with hypoallergenic shampoos to remove antigen from the skin.

 Create mechanical barriers, if possible – socks, shirts, restriction from environment.