Contact Allergy Hypersensitivity — MFDS Part 1 MCQ

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ModeratePhysiologyContact Allergy HypersensitivityMFDS Part 1

A dental healthcare worker develops a localised pruritic eczematous eruption 36 hours after wearing natural-rubber gloves. Patch testing identifies sensitisation to a thiuram rubber accelerator. The same hypersensitivity mechanism accounts for contact allergy to nickel released from a dental alloy. Which type of hypersensitivity reaction is involved?

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Correct answer: E — Type IV (delayed, T-cell-mediated)

The correct answer is E. The delayed local eczematous eruption and positive patch test to thiuram identify allergic contact dermatitis, a type IV reaction mediated by sensitised T lymphocytes. Nickel contact allergy has the same mechanism. Type I is the principal distractor because natural rubber latex proteins can cause immediate IgE-mediated urticaria, respiratory symptoms or anaphylaxis; however, delayed glove dermatitis is generally associated with rubber-processing chemicals such as thiurams or carbamates. Type II reactions involve antibodies directed against cell-surface or tissue antigens, type III reactions result from immune-complex deposition, and type V reactions involve stimulatory receptor antibodies. None accounts for delayed, patch-test-positive contact dermatitis.

Reference: Norfolk and Norwich University Hospitals NHS Foundation Trust. Trust Guideline for the Prevention and Management of Latex Allergy and Occupational Skin Disorders, sections 1.1.2–1.1.3, 2023. https://www.nnuh.nhs.uk/publication/download/latex-allergy-and-occupational-skin-disorders-prevention-and-management-ca2076-v6/