A systemic allergic contact dermatitis may present with one or more patterns of dermal involvement. The "baboon syndrome" involves erythema of the buttocks, resembling the red buttocks of a baboon.
The contact allergen may be ingested, injected, inhaled or absorbed transcutaneously.
Clinical features:
(1) diffuse erythema of the buttocks, genital area and upper inner surface of the thighs
(2) variable erythema of the axillae
(3) variable erythema of the flexor surfaces at the elbow (antecubital fossa) and popliteal fossa
The involved area may show a color that ranges from dark violet to pink.
Additional testing to identify the causative allergen:
(1) patch testing - may be negative in some patients despite extensive testing
(2) oral ingestion of a candidate allergen (oral provocation test)
Differential diagnosis: contact dermatitis to an allergen in underwear
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