Lupus vulgaris — DTM&H MCQ

Correct answer: D — Lupus vulgaris (cutaneous tuberculosis)

The correct answer is D, lupus vulgaris (cutaneous tuberculosis). This is the classic presentation of paucibacillary cutaneous TB: a chronic, painless, well-demarcated scalp plaque progressing to scarring alopecia, with satellite papules representing serpiginous extension at the plaque edge, and biopsy confirming caseating granulomatous inflammation with acid-fast bacilli. Lupus vulgaris typically arises from haematogenous, lymphatic or contiguous spread of Mycobacterium tuberculosis in a person with pre-existing immunity, explaining the indolent, destructive but low-bacillary course. Management follows standard multidrug anti-tuberculous therapy as for any active TB site, since extrapulmonary and cutaneous TB are treated with the same regimen as pulmonary disease. Why the other options are wrong: B. Alopecia areata: This is an autoimmune, non-scarring alopecia with smooth bald patches and no granulomas, AFB, or satellite lesions; biopsy shows peribulbar lymphocytic infiltrate, not granulomatous inflammation. E. Discoid lupus erythematosus: Causes scarring alopecia but biopsy shows interface dermatitis with follicular plugging and basement membrane thickening, not caseating granulomas or AFB. C. Tinea capitis: A dermatophyte infection causing scaling, broken hairs and sometimes kerion, but fungal elements (not AFB) are seen on staining and granulomatous AFB-positive histology is absent. A. Lepromatous leprosy of the scalp: Produces diffuse infiltration and madarosis rather than a well-circumscribed scarring plaque, and biopsy shows numerous acid-fast bacilli within a foamy macrophage (lepromatous) infiltrate rather than tuberculoid granulomas, with a different clinical distribution (symmetrical, cooler body sites). Key point: A chronic scarring scalp plaque with satellite papules and AFB-positive granulomas on biopsy is diagnostic of lupus vulgaris, the paucibacillary reactivation form of cutaneous tuberculosis.

Reference: NICE Guideline NG33, Tuberculosis (2016, updated), Recommendations on drug treatment of active TB (extrapulmonary sites treated with the same regimen as pulmonary TB): isoniazid, rifampicin, pyrazinamide and ethambutol for 2 months, then isoniazid and rifampicin for a further 4 months. https://www.nice.org.uk/guidance/ng33/chapter/recommendations