## Clinical Features Analysis **Key Point:** The diagnosis of tuberculoid leprosy is based on the Ridley-Jopling classification, which relies on clinical, bacteriological, and immunological features. ### Diagnostic Criteria Met | Feature | Finding | Significance | |---------|---------|---------------| | Number of lesions | Single lesion | Tuberculoid (1–5 lesions) | | Sensory loss | Complete (light touch + temperature) | Tuberculoid (early and complete) | | Nerve thickening | Absent | Tuberculoid (minimal) | | Slit-skin smear | Negative (0 bacilli) | Tuberculoid (paucibacillary, <5 lesions) | | Border definition | Well-defined | Tuberculoid (sharp, clear borders) | | Lesion size | 4 cm × 3 cm | Consistent with tuberculoid | **High-Yield:** Tuberculoid leprosy is the **paucibacillary** form with strong cell-mediated immunity (Th1 response), resulting in: - Few lesions (1–5) - Negative or scanty bacilli on slit-skin smear - Early, complete sensory loss - Well-demarcated lesions - Minimal systemic involvement **Clinical Pearl:** The presence of **complete sensory loss in a single well-demarcated lesion with negative bacteriology** is pathognomonic for tuberculoid leprosy. The patient's strong immune response has contained the infection. ### Ridley-Jopling Classification Spectrum ```mermaid flowchart LR A["Tuberculoid<br/>(TT)"]:::outcome --> B["Borderline<br/>Tuberculoid<br/>(BT)"]:::outcome --> C["Mid-Borderline<br/>(BB)"]:::outcome --> D["Borderline<br/>Lepromatous<br/>(BL)"]:::outcome --> E["Lepromatous<br/>(LL)"]:::outcome A -->|Strong immunity| F["Paucibacillary<br/>Few lesions<br/>Negative smear"]:::action E -->|Weak immunity| G["Multibacillary<br/>Many lesions<br/>Positive smear"]:::action ``` **Mnemonic:** **TT-BT-BB-BL-LL** — The spectrum from **strong to weak** cell-mediated immunity. 
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