Leprosy multibacillary disease — DTM&H MCQ

Correct answer: B — Multibacillary leprosy

The correct answer is B, multibacillary leprosy. This patient has multiple hypopigmented, anaesthetic plaques, thickened ulnar nerves and a positive slit-skin smear, and under the WHO operational classification (used in UK practice), a positive slit-skin smear automatically places a case in the multibacillary category regardless of lesion count, because it confirms a high bacillary load. Multiple lesions with nerve trunk enlargement further support extensive dissemination typical of the lepromatous/borderline lepromatous end of the spectrum. This classification is critical because it dictates a longer, three-drug multidrug therapy regimen rather than the shorter paucibacillary regimen. Nerve involvement here also flags a real risk of reaction-related nerve damage requiring monitoring. Why the other options are wrong: E. Tinea corporis: Produces scaly, itchy annular plaques with an active advancing edge, not anaesthetic hypopigmented patches, and does not cause nerve thickening or a positive slit-skin smear. A. Paucibacillary leprosy: This is excluded specifically because a positive slit-skin smear denotes multibacillary disease irrespective of the number of lesions; paucibacillary cases are smear-negative. D. Vitiligo: Causes depigmented (not hypopigmented) macules with normal sensation and no nerve involvement or bacilli on smear. C. Post-kala-azar dermal leishmaniasis: Presents with hypopigmented or nodular lesions after visceral leishmaniasis treatment, typically in East Africa or the Indian subcontinent, but lesions retain normal sensation and there is no nerve thickening or acid-fast bacilli on skin smear. Key point: A positive slit-skin smear defines multibacillary leprosy regardless of the number of skin lesions present.

Reference: UK Health Security Agency, Memorandum on Leprosy, 2023 (gov.uk), section on classification and slit-skin smear testing