A 32-year-old man from rural Maharashtra presents with a single hypopigmented macule on his left forearm with well-defined borders and complete loss of sensation. Slit-skin smear from the lesion shows no acid-fast bacilli (AFB). His household contacts are asymptomatic. Which classification of leprosy does this patient have?

Explanation

## Clinical Diagnosis: Tuberculoid Leprosy ### Key Clinical Features in This Case **Key Point:** The patient presents with a **single well-demarcated hypopigmented lesion** with **complete sensory loss** and **negative slit-skin smear** — all hallmarks of tuberculoid leprosy (TT). ### Ridley-Jopling Classification Table | Feature | Tuberculoid (TT) | Borderline TB (BT) | Mid-Borderline (BB) | Borderline LL (BL) | Lepromatous (LL) | |---------|---|---|---|---|---| | **Number of lesions** | 1–5 (few) | Few to moderate | Moderate to many | Many | Numerous, ill-defined | | **Sensory loss** | Complete | Complete | Incomplete | Incomplete | Late/absent | | **Nerve involvement** | Early, marked | Marked | Moderate | Mild | Late | | **Slit-skin smear** | Negative (0) | Negative (0) | 1–2+ | 3–4+ | 5–6+ | | **Histology** | Epithelioid granulomas | Epithelioid granulomas | Mixed | Foamy macrophages | Foamy macrophages | | **Immunity** | Strong cell-mediated | Strong | Moderate | Weak | Very weak | **High-Yield:** The **single lesion + complete sensory loss + negative smear** triad is **pathognomonic for tuberculoid leprosy**. ### Why Tuberculoid? 1. **Few lesions** (1 in this case) — TT is paucibacillary 2. **Well-defined borders** — indicates strong host immunity 3. **Complete anesthesia** — early and marked nerve involvement 4. **Negative slit-skin smear** — low bacillary load due to robust cell-mediated immunity ### Immunological Basis **Clinical Pearl:** Tuberculoid leprosy represents the **strong end of the Ridley-Jopling spectrum** — the host's robust Th1-mediated (cell-mediated) immune response effectively contains *Mycobacterium leprae*, resulting in few lesions, early nerve damage, and minimal bacilli. ### Mnemonic: "TT = Tiny in number, Tremendous immunity" - **T**uberculoid = **T**iny lesions (few), **T**remendous cell-mediated immunity - Few lesions, early nerve damage, negative smear, strong granulomas [cite:Park 26e Ch 8]