Lupus Vulgaris — SCE Dermatology MCQ

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HardCutaneous InfectionLupus VulgarisSCE Dermatology

A 32-year-old woman presents with a chronic erythematous scaly plaque on her shin that shows characteristic apple jelly nodules on diascopy. Biopsy shows caseating granulomas with acid-fast bacilli on Ziehl-Neelsen staining. Mycobacterium tuberculosis is confirmed on culture. What is the diagnosis?

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Correct answer: C — Lupus vulgaris (cutaneous tuberculosis)

Lupus vulgaris is the most common form of cutaneous tuberculosis in post-primary (previously sensitised) individuals. It presents as a slowly progressive reddish-brown plaque with characteristic apple jelly nodules on diascopy (similar appearance to sarcoidosis, but with caseating granulomas rather than non-caseating). Histologically, caseating granulomas with Langhans giant cells are seen. ZN stain may show acid-fast bacilli (though yield is low). TB culture or PCR confirms the diagnosis. Treatment is standard anti-TB therapy (Isoniazid, Rifampicin, Pyrazinamide, Ethambutol for 2 months, then Isoniazid/Rifampicin for 4 months). If untreated, SCC can develop in longstanding lesions.

Reference: BAD 2016; NICE NG33 TB