In the Ridley-Jopling classification of leprosy, a patient has 4 skin lesions, poorly defined borders, reduced but not absent sensation, and biopsy shows foamy macrophages with many bacilli and no lymphocytic infiltrate. What type of leprosy is this, and what is the lepromin test result?

• A Lepromatous leprosy (LL); lepromin test negative ✓
• B Tuberculoid leprosy (TT); lepromin test strongly positive
• C Borderline tuberculoid (BT); lepromin test weakly positive
• D Borderline lepromatous (BL); lepromin test weakly negative

Explanation

Lepromatous leprosy (LL) represents the anergic pole with high bacillary load (multibacillary, BI ≥4+), foamy macrophages (Virchow cells) laden with M. leprae, and diffuse skin infiltration with poorly defined lesions. Cell-mediated immunity is specifically suppressed, so the lepromin (Mitsuda) test is negative. Tuberculoid leprosy (TT) has the opposite: strong CMI, few bacteria, well-defined anaesthetic plaques, and strongly positive lepromin. MDT for LL/MB leprosy is rifampicin + dapsone + clofazimine for 12 months.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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