Leprosy WHO classification — DTM&H MCQ

Correct answer: A — Exactly 1 lesion

The correct answer is A, exactly 1 lesion. Under the WHO operational classification, leprosy is graded purely on the number of skin lesions to allow field diagnosis without laboratory support: single-lesion paucibacillary (PB) disease requires exactly one skin lesion with loss of sensation (as in this child's solitary anaesthetic hypopigmented patch), standard PB disease covers 2 to 5 lesions, and multibacillary (MB) disease is more than 5 lesions. The single-lesion category exists as a distinct entity because it identifies patients suitable for the abbreviated single-dose ROM regimen (rifampicin, ofloxacin, minocycline) rather than the standard 6-month PB course, reflecting the very low bacillary load typical of a solitary tuberculoid lesion with one enlarged peripheral nerve. This child's presentation, a single well-defined, hypopigmented, anaesthetic patch with one enlarged epitrochlear nerve, fits precisely this single-lesion PB category. Why the other options are wrong: C. Up to 3 lesions: This threshold does not correspond to any WHO leprosy category; PB disease is defined as 2 to 5 lesions once more than one lesion is present, so 3 lesions would simply be standard PB, not single-lesion PB. D. Up to 5 lesions: This is the definition of the broader paucibacillary group as a whole, not the single-lesion subtype, which by definition requires only one lesion. B. Any number with negative smears: The operational classification is based on lesion count and nerve involvement for field use precisely because skin smears are not routinely available; smear status is not the defining criterion. E. Up to 2 lesions: Two lesions already places a patient in the standard paucibacillary category (2 to 5 lesions), which is treated with 6 months of rifampicin and dapsone, not the single-dose ROM regimen. Key point: Single-lesion paucibacillary leprosy is defined strictly as exactly one skin lesion, distinguishing it from standard PB (2 to 5 lesions) and determining eligibility for single-dose ROM therapy rather than 6-month MDT.

Reference: World Health Organization, Treatment of Leprosy (multidrug therapy classification by number of skin lesions), who.int/teams/control-of-neglected-tropical-diseases/leprosy/treatment; see also Hospital for Tropical Diseases London cohort study on leprosy MDT management, PMC11658689