A 28-year-old woman from Odisha presents with a single well-demarcated hypopigmented macule on her forearm with impaired sensation. Slit-skin smear is negative for acid-fast bacilli. Histopathology shows epithelioid cell granulomas with few or no bacilli. Which is the most common type of leprosy in the Indian population?

Explanation

## Most Common Type of Leprosy in India **Key Point:** Tuberculoid leprosy (TT) is the most common form of leprosy in India, accounting for approximately 60–70% of all leprosy cases. ### Ridley-Jopling Classification: Frequency in India | Type | Frequency (%) | AFB Load | Lesions | Nerve Involvement | | --- | --- | --- | --- | --- | | **Tuberculoid (TT)** | **60–70%** | **Rare (0–1)** | **1–5, well-demarcated** | **Early, severe** | | Borderline tuberculoid (BT) | 10–15% | Few (1–5) | Multiple, asymmetric | Moderate | | Borderline (BB) | 5–10% | Moderate (4–6) | Many, mixed | Variable | | Borderline lepromatous (BL) | 5–10% | Numerous (4–6) | Many, poorly defined | Late | | Lepromatous (LL) | 5–10% | Abundant (6) | Innumerable, symmetric | Very late | | Indeterminate | <5% | Variable | Ill-defined macules | Minimal | **High-Yield:** Tuberculoid leprosy is the most common form because it represents a **strong cell-mediated immune response** to M. leprae. Patients with good immunity mount an effective granulomatous response, limiting bacterial dissemination. ### Why Tuberculoid is Most Common 1. **Immune Response:** Strong Th1-mediated (IL-2, IFN-γ) cell-mediated immunity 2. **Bacterial Load:** Paucibacillary (few or no bacilli visible on smear) 3. **Clinical Features:** Few, well-demarcated, hypopigmented lesions with sharp borders 4. **Nerve Involvement:** Early and severe (often the presenting symptom) 5. **Prognosis:** Better with appropriate treatment; lower relapse rates **Mnemonic:** **T**uberculoid = **T**herapy-responsive, **T**ight control (strong immunity), **T**ypically few lesions ### Contrast with Lepromatous Leprosy Lepromatous leprosy (LL) represents the **opposite end of the spectrum**—weak cell-mediated immunity allows uncontrolled bacterial multiplication, resulting in: - Bacillary load of 10^6–10^9 organisms - Innumerable ill-defined lesions - Late nerve involvement - Higher infectivity and relapse risk **Clinical Pearl:** The single well-demarcated lesion with impaired sensation and negative smear in the vignette is classic for tuberculoid leprosy—the paucibacillary form that dominates Indian epidemiology. [cite:Park 26e Ch 8; Robbins 10e Ch 8]