A 32-year-old man from rural Maharashtra presents with a single hypopigmented macule on his left forearm with well-defined borders and loss of sensation. Slit-skin smear from the lesion shows 0 bacilli per oil immersion field. Lepromin test performed at 3 weeks is strongly positive. Which classification of leprosy does this patient have?

Explanation

## Clinical Diagnosis: Tuberculoid Leprosy ### Key Diagnostic Features **Key Point:** The combination of a single or few well-demarcated hypopigmented lesions with complete sensory loss, negative slit-skin smear (0 bacilli), and a strongly positive lepromin test is pathognomonic for **tuberculoid leprosy (TT)**. ### Classification Framework Leprosy is classified using the **Ridley-Jopling classification**, which is based on: 1. Number and distribution of skin lesions 2. Bacterial load (slit-skin smear) 3. Lepromin test (delayed-type hypersensitivity) 4. Histopathology | Feature | Tuberculoid (TT) | Borderline TB (BT) | Mid-Borderline (BB) | Borderline LL (BL) | Lepromatous (LL) | | --- | --- | --- | --- | --- | --- | | **Number of lesions** | 1–5 | Few to moderate | Moderate to many | Many | Innumerable | | **Slit-skin smear** | 0 bacilli | 1–5 bacilli | 4–5+ bacilli | 4–5+ bacilli | 5–6+ bacilli | | **Lepromin test** | Strongly positive | Positive | Weakly positive | Negative | Negative | | **Sensory loss** | Complete | Complete | Incomplete | Incomplete | Absent/late | | **Immune response** | Strong cell-mediated | Strong CMI | Moderate | Weak | Absent | ### Clinical Pearls **Clinical Pearl:** In tuberculoid leprosy, the patient mounts a robust **Th1-mediated cell-mediated immune response**, which: - Limits bacillary multiplication (hence 0 bacilli in slit-skin smear) - Creates well-demarcated, few lesions - Produces strong lepromin positivity (Mitsuda test) - Results in complete sensory loss within lesions due to intense granulomatous inflammation of nerves **High-Yield:** Tuberculoid leprosy is the **most favorable** end of the spectrum with excellent prognosis, minimal disability risk, and shortest treatment duration (6 months for single lesion). ### Why This Is NOT Other Forms - **Borderline TB:** Would have more lesions (5–10) and weakly positive lepromin test - **Mid-Borderline:** Would have many lesions with positive slit-skin smear (4–5+ bacilli) - **Lepromatous:** Would have innumerable lesions, high bacillary load, and negative lepromin test **Mnemonic:** **T-T-T for Tuberculoid**: **T**wo or fewer lesions, **T**ight (well-demarcated) borders, **T**est positive (lepromin) [cite:Park 26e Ch 24]