A 32-year-old man from rural Maharashtra with borderline tuberculoid leprosy (BT) on multidrug therapy (MDT) for 3 months presents with acute onset of painful nodules on his face, arms, and trunk. On examination, he has fever (38.5°C), tender erythematous nodules, and hepatosplenomegaly. His leprosy bacillary index has increased. Histopathology shows neutrophilic infiltration with immune complex deposition. What is the most likely diagnosis?

Explanation

## Diagnosis: Type 2 Lepra Reaction (Erythema Nodosum Leprosum) ### Clinical Presentation The patient presents with: - Acute onset painful nodules on face, arms, and trunk - Systemic symptoms: fever, hepatosplenomegaly - Occurs during or after MDT (3 months into treatment) - Increased bacillary index ### Pathophysiology **Key Point:** Type 2 lepra reaction is an **immune complex-mediated (Type III hypersensitivity)** reaction that occurs in lepromatous (L) and borderline lepromatous (BL) leprosy. **High-Yield:** Type 2 reactions are associated with: - Antigen-antibody complex deposition in skin and organs - Neutrophilic infiltration (not epithelioid cells) - Occurs in patients with high bacillary loads (L and BL) - Can occur during treatment or years after completion ### Differential Features | Feature | Type 1 Reaction | Type 2 Reaction (ENL) | |---------|-----------------|----------------------| | **Leprosy type** | BT, BL, BB (unstable) | L, BL (high bacillary load) | | **Timing** | During/after treatment | During/after treatment | | **Mechanism** | Cell-mediated (Type IV) | Immune complex (Type III) | | **Histology** | Epithelioid cells, granulomas | Neutrophilic infiltration, IC deposition | | **Lesions** | Existing lesions become inflamed | New painful nodules, pustules | | **Systemic signs** | Mild/absent | Prominent (fever, hepatomegaly, neuritis) | | **Bacillary index** | Decreases | Unchanged or increases | ### Why Type 2 Here? This patient has: 1. **High bacillary load** (increased bacillary index) — prerequisite for Type 2 2. **Immune complex histology** (stated in stem) 3. **Systemic manifestations** (fever, hepatosplenomegaly, neuritis risk) 4. **Painful nodules** (characteristic of ENL, not Type 1) 5. **BL classification** — Type 2 is common in BL and L **Clinical Pearl:** Type 2 lepra reaction (ENL) is sometimes called "lepra reaction of the lepromatous type" and represents the immune system's response to high antigen load from dead bacilli. ### Management Approach ```mermaid flowchart TD A[Type 2 Lepra Reaction Suspected]:::outcome --> B{Severity?}:::decision B -->|Mild| C[NSAIDs + Continue MDT]:::action B -->|Moderate| D[Prednisolone 0.5-1 mg/kg/day]:::action B -->|Severe/Neuritis| E[Prednisolone 1-2 mg/kg/day + Thalidomide]:::action C --> F[Monitor for resolution]:::action D --> F E --> F F --> G[Taper steroids over weeks]:::action ``` **Mnemonic:** **ENL = Erythema Nodosum Leprosum = Exudative Nodules + Lepromatous type** **High-Yield:** Thalidomide is the gold standard for ENL (Type 2) in patients who fail steroids or have contraindications. It works by TNF-α inhibition and is highly effective.