In leprosy, the Ridley-Jopling classification is based on the immune spectrum. A patient has 4 skin lesions with well-defined edges, diminished sensation, negative slit-skin smear (BI = 0), and positive lepromin test. Where does this patient fall on the spectrum, and what WHO treatment regimen applies?

• A Multibacillary leprosy: WHO MB regimen — dapsone + rifampicin + clofazimine × 12 months
• B Lepromatous leprosy (LL): high bacterial load, negative lepromin, requires MB regimen for 24 months
• C Pure neuritic leprosy: treated with PB regimen only if no skin patches are present
• D Paucibacillary leprosy (borderline tuberculoid — BT or TT end): WHO PB regimen — dapsone 100 mg daily + rifampicin 600 mg monthly supervised × 6 months ✓

Explanation

Tuberculoid (TT) and borderline tuberculoid (BT) leprosy are paucibacillary (PB) — defined by ≤5 skin patches, well-defined hypopigmented anesthetic lesions, negative slit-skin smear (BI 0), and positive lepromin test (strong CMI). WHO classifies PB leprosy as ≤5 patches and treats with 6 months of dapsone 100 mg/day (self-administered) + rifampicin 600 mg once monthly (supervised). Multibacillary (MB) leprosy (≥6 patches or positive smear) requires triple therapy (dapsone + rifampicin + clofazimine) for 12 months.

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

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