Buruli ulcer — DTM&H MCQ

Correct answer: B — Buruli ulcer

The correct answer is B, Buruli ulcer. This West African child has the classic triad of a painless, progressively enlarging leg ulcer with undermined edges and a necrotic base, caused by Mycobacterium ulcerans, an acid fast bacillus that stains positive on ZN smear. The organism produces the toxin mycolactone, which causes tissue necrosis, immunosuppression locally and destruction of nerve endings, explaining the striking absence of pain despite extensive tissue destruction. Ghana is one of the highest burden countries for this disease, and the combination of chronicity, undermining, painlessness and AFB positivity is pathognomonic in this endemic setting. Why the other options are wrong: C. Cutaneous tuberculosis: lupus vulgaris and scrofuloderma are typically slow growing plaques or sinuses over lymph nodes, not painless undermined ulcers, and while ZN can occasionally show AFB, M. tuberculosis skin disease is far less common than Buruli ulcer in this exact clinical and geographic pattern. E. Cutaneous leishmaniasis: produces a painless ulcer but with a raised, indurated border rather than undermined edges, and the organism seen on smear is intracellular amastigotes on Giemsa stain, not acid fast bacilli. A. Tropical ulcer: these are typically rapidly developing, painful ulcers on the lower leg following minor trauma, with a purulent rather than necrotic base, and no AFB are seen. D. Yaws: caused by Treponema pallidum pertenue, presents with papillomas and later punched out ulcers, but these are not undermined and the organism is a spirochaete, not detected by ZN stain. Key point: painless, undermined, necrotic leg ulcer with AFB on ZN stain in a West African child is Buruli ulcer (Mycobacterium ulcerans) until proven otherwise.

Reference: World Health Organization, Buruli ulcer (Mycobacterium ulcerans infection) Fact Sheet, 2024, https://www.who.int/news-room/fact-sheets/detail/buruli-ulcer-(mycobacterium-ulcerans-infection)