Contact Dermatitis — SCE Dermatology MCQ

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EasyInflammatory DermatosesContact DermatitisSCE Dermatology

A 35-year-old woman with suspected contact dermatitis undergoes patch testing. Her dermatologist explains the reading schedule. According to ICDRG recommendations, when are patch test readings performed?

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Correct answer: A — Day 2 (48 hours) and Day 4 (96 hours)

The International Contact Dermatitis Research Group (ICDRG) recommends patch test readings at Day 2 (48 hours — when patches are removed) and Day 4 (96 hours — the definitive reading). The 96-hour reading is essential because some allergens (e.g., neomycin, corticosteroids, metals) show delayed reactions that are only positive at 96 hours. Additional readings at Day 7 may be needed for some allergens (gold, corticosteroids). Reactions are graded: + (erythema, infiltration, papules), ++ (erythema, infiltration, papules, vesicles), +++ (bullous reaction), IR (irritant reaction), ? (doubtful/macular erythema only). Irritant reactions must be distinguished from true allergic reactions.

Reference: BAD 2017 Contact Dermatitis Guidelines; ICDRG