Drug-Induced Lichenoid Reaction — MFDS Part 1 MCQ
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Correct answer: B — Asymmetrical lesions developed after starting a potentially causative medicine
Explanation lettering: C = shown as A · A = shown as B · B = shown as C
A is correct. Drug-induced oral lichenoid reactions can closely mimic oral lichen planus, but asymmetry combined with a temporal relationship to a potentially causative medicine favours a drug reaction. Idiopathic oral lichen planus commonly has a bilateral, symmetrical distribution. Reticular white striae and buccal mucosal involvement may occur in both conditions. Histology is also not decisive because both can show a similar lichenoid interface inflammatory pattern. Candida may coexist with oral mucosal disease but does not cause a lichenoid drug reaction. Improvement after prescriber-supervised withdrawal can strengthen the diagnosis, although improvement is not universal and may be delayed; a dentist should not independently discontinue an essential medicine.
Reference: University Hospitals of North Midlands NHS Trust. Lichen planus: Patient Information Leaflet, reapproved September 2025. https://www.uhnm.nhs.uk/media/boyj3lil/agenda-item-reapproved-lichen-planus.pdf