## Lepra Reactions: Classification and Epidemiology **Key Point:** Type 2 lepra reaction (erythema nodosum leprosum, ENL) is the most common lepra reaction overall, occurring in approximately 50% of lepromatous leprosy (LL) patients and 10% of borderline lepromatous leprosy (BL) patients. ### Clinical Context of Type 2 Lepra Reaction **High-Yield:** ENL typically occurs: - During treatment (most common) or within 1 year of starting therapy - In patients with high bacillary loads (LL and BL forms) - As an immune complex-mediated reaction (Type III hypersensitivity) ### Distinguishing Features of Lepra Reactions | Feature | Type 1 (Reversal) | Type 2 (ENL) | |---------|-------------------|---------------| | **Timing** | Months to years (any time) | During/after treatment (early) | | **Leprosy type** | BT, BL, LL | LL, BL | | **Frequency** | 10–15% of cases | 50% of LL, 10% of BL | | **Mechanism** | Cell-mediated (Type IV) | Immune complex (Type III) | | **Lesions** | Existing lesions become inflamed | New painful nodules, systemic signs | | **Systemic features** | Mild | Prominent (fever, arthralgia, neuritis) | | **Histology** | Epithelioid cell granulomas | Neutrophilic infiltrate | **Clinical Pearl:** The presence of systemic symptoms (fever, arthralgia, lymphadenopathy) and painful subcutaneous nodules in a patient on anti-leprosy therapy is pathognomonic for Type 2 lepra reaction. **Mnemonic:** **ENL = Early, Nodular, Lepromatous** - **E**arly: occurs during or shortly after starting treatment - **N**odular: painful nodules are the hallmark - **L**epromatous: occurs in LL and BL forms with high bacillary loads ### Why Type 2 is Most Common Type 2 lepra reaction occurs in approximately 50% of lepromatous leprosy patients because: 1. High antigen load triggers immune complex formation 2. Treatment causes bacterial antigen release, amplifying immune response 3. Occurs predictably in the early treatment phase Type 1 reactions are less frequent (10–15%) and occur across a broader time spectrum, making Type 2 the most common acute lepra reaction in clinical practice.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.