A 48-year-old woman with lepromatous leprosy (LL) on MDT for 8 months presents with sudden onset of painful tender nodules on her face, arms, and legs. She has fever (39°C), generalized lymphadenopathy, hepatosplenomegaly, and painful neuritis. Lepromin test is negative. Histopathology of a nodule shows neutrophilic infiltration with immune complex deposition. Which lepra reaction is this, and what is the appropriate initial management?

Explanation

## Diagnosis: Erythema Nodosum Leprosum (ENL / Type 2 Lepra Reaction) **Key Point:** ENL is an immune complex-mediated (Type III hypersensitivity) reaction that occurs in lepromatous leprosy (LL, BL) with a NEGATIVE lepromin test. It typically manifests 6+ months into MDT when the bacillary load is high and immune complexes accumulate. ### Clinical Features of ENL (Type 2 Reaction) **High-Yield:** ENL occurs **only in LL and BL** (lepromatous end of spectrum) and is characterized by: - Painful tender nodules (often on face, arms, legs) - Fever and systemic symptoms - Hepatosplenomegaly and lymphadenopathy - Neuritis (often painful) - Iritis and anterior uveitis - **Negative lepromin test** (low CMI) - Timing: 6+ months into treatment (when bacillary load is high) ### Pathophysiology **Mnemonic: ENL = Immune Complex Disease** - **E**rythema nodosum leprosum - **N**eutrophilic infiltration - **L**epromatous leprosy (LL/BL only) ```mermaid flowchart TD A[Lepromatous leprosy with high bacillary load]:::outcome --> B[Antigen-antibody complex formation]:::action B --> C[Immune complex deposition in tissues]:::action C --> D[Complement activation Type III HSR]:::action D --> E[Neutrophilic infiltration]:::outcome E --> F[Tender nodules, fever, systemic symptoms]:::outcome G[Negative lepromin test]:::outcome --> H[Low cell-mediated immunity]:::outcome style A fill:#ffebee style F fill:#ffcdd2 ``` ### Histopathology - Neutrophilic infiltration (NOT lymphocytic) - Immune complex deposition (IgG, IgM, C3) - Vasculitis of small vessels - Leukocytoclasia may be present ### Type 1 vs Type 2 (ENL) — Quick Comparison | Feature | Type 1 Reaction | ENL (Type 2) | |---------|-----------------|---------------| | **Leprosy type** | Borderline (BT, BB, BL) | Lepromatous (LL, BL) | | **Lepromin test** | **Positive** | **Negative** | | **Hypersensitivity** | Type IV (CMI) | Type III (immune complex) | | **Histology** | Epithelioid cells, lymphocytes | Neutrophils, immune complexes | | **Timing** | Early in treatment | 6+ months into treatment | | **Nodule character** | Erythematous plaques | Tender, painful nodules | | **Systemic signs** | Mild | Marked (fever, hepatosplenomegaly) | **Clinical Pearl:** The **negative lepromin test** is the key discriminator between Type 1 (positive lepromin) and ENL (negative lepromin). ### Management of ENL **High-Yield:** Management depends on severity: 1. **Mild ENL** (few nodules, no systemic symptoms): - Continue MDT - NSAIDs (aspirin, ibuprofen) - Observation 2. **Moderate ENL** (multiple nodules, fever, mild systemic involvement): - Continue MDT - Corticosteroids (prednisolone 0.5–1 mg/kg/day, tapered over 3–6 months) - NSAIDs 3. **Severe ENL** (extensive nodules, high fever, hepatosplenomegaly, neuritis, iritis): - **Thalidomide** (100–400 mg/day) — **GOLD STANDARD** for severe ENL - OR Corticosteroids if thalidomide contraindicated - Continue MDT - Supportive care **Warning:** Thalidomide is teratogenic — absolute contraindication in pregnancy. Requires strict contraception and enrollment in risk minimization program. ### Why This Patient Needs Thalidomide This patient has **severe ENL** with: - Fever (39°C) - Hepatosplenomegaly - Generalized lymphadenopathy - Painful neuritis - Immune complex deposition on histology Thalidomide is the drug of choice for severe ENL because it: - Inhibits TNF-α production - Suppresses immune complex formation - Provides rapid symptomatic relief - Allows continuation of MDT [cite:Park 26e Ch 9; Robbins 10e Ch 23]