skip to main content

Patch Test Interpretation — SCE Dermatology MCQ

Instant feedback + full explanation. One question, done properly.

ModerateInflammatory DermatosesPatch Test InterpretationSCE Dermatology

A 40-year-old woman has chronic hand eczema and is referred for patch testing. Her dermatologist applies patches on Monday and reads on Wednesday (D2) and Friday (D4). On D2, one allergen shows a faint macular erythema only. On D4, it has developed into erythema with infiltration and papules. How should this be interpreted?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — Delayed positive allergic reaction — some allergens (particularly metals, corticosteroids, neomycin) show delayed positivity emerging at D4; this is a genuine positive reaction

The correct answer is D: Delayed positive allergic reaction, some allergens (particularly metals, corticosteroids, neomycin) show delayed positivity emerging at D4, and this is a genuine positive reaction. The evolution from faint macular erythema on D2 to erythema with infiltration and papules on D4 is a crescendo pattern characteristic of true allergic sensitisation rather than an irritant effect. Certain allergens on the standard series, notably metals, corticosteroids (tixocortol pivalate, budesonide) and neomycin, are well recognised to react late, which is why UK guidance mandates a D4 reading rather than relying on D2 alone. The reaction has progressed from flat erythema to an infiltrated, papular morphology, satisfying criteria for a positive allergic response, unlike an irritant reaction which typically peaks early and fades.

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/skin-conditions