A 32-year-old man from rural Maharashtra presents with hypopigmented macules on his face, trunk, and extensor surfaces for 8 months. On examination, he has loss of sensation over the lesions and thickened nerves. Slit-skin smear shows 4+ acid-fast bacilli. He is started on multidrug therapy (MDT) for lepromatous leprosy. After 2 weeks of treatment, he develops fever, painful nodules, and worsening of existing lesions with signs of systemic inflammation. What is the most likely diagnosis of this clinical event?

Explanation

## Clinical Recognition of ENL **Key Point:** Erythema nodosum leprosum (ENL, also called Lepra reaction type 2) is an immune complex-mediated reaction that occurs in lepromatous and borderline lepromatous leprosy patients, typically 1–2 weeks after starting MDT or during treatment. ### Pathophysiology ENL is a Type III hypersensitivity reaction (immune complex deposition) triggered by: - Sudden release of mycobacterial antigens during effective chemotherapy - Formation of antigen–antibody complexes - Deposition in skin, nerves, eyes, and systemic organs ### Clinical Features of ENL | Feature | Details | |---------|----------| | **Timing** | 1–2 weeks after MDT initiation (can occur up to 5 years later) | | **Skin** | Painful, tender nodules; erythematous papules; may ulcerate | | **Systemic** | Fever, malaise, lymphadenopathy | | **Neuritis** | Acute worsening of nerve pain and dysfunction | | **Ocular** | Iritis, keratitis, anterior uveitis | | **Constitutional** | Hepatosplenomegaly, arthralgia | ### Diagnosis **High-Yield:** ENL diagnosis is **clinical**; there is no specific test. Features supporting ENL in this case: - Lepromatous leprosy background (4+ bacilli) - Onset 2 weeks after MDT initiation - Painful nodules (not painless like type 1 reaction) - Systemic inflammation (fever) - Worsening of existing lesions ### Management 1. **Continue MDT** — do not stop antileprotic drugs 2. **NSAIDs** — for mild ENL (aspirin, ibuprofen) 3. **Corticosteroids** — prednisolone 0.5–1 mg/kg/day for moderate to severe ENL; taper over weeks 4. **Thalidomide** — 100–400 mg/day for severe, recurrent ENL (highly effective but teratogenic; requires strict contraception) 5. **Supportive care** — analgesics, eye care if iritis present **Clinical Pearl:** ENL can be life-threatening if it involves vital organs (neuritis → nerve damage, iritis → blindness, hepatitis). Early recognition and treatment with corticosteroids prevent morbidity. ### Contrast with Type 1 Reaction (Reversal Reaction) | Feature | Type 1 (Reversal) | Type 2 (ENL) | |---------|-------------------|---------------| | **Mechanism** | Cell-mediated (Type IV) | Immune complex (Type III) | | **Timing** | Can occur anytime (before, during, after MDT) | 1–2 weeks after MDT start | | **Lesions** | Painless; existing lesions become inflamed | Painful nodules; new lesions | | **Systemic signs** | Minimal | Prominent (fever, malaise) | | **Bacillary load** | Occurs in TT, BT, BL forms | **Only in LL and BL** | | **Slit-skin smear** | May show organisms | High bacillary load (4+) | | **Treatment** | Corticosteroids; continue MDT | Corticosteroids ± thalidomide; continue MDT | **Mnemonic: ENL = Early, Nodular, Lepromatous** - **E**arly: 1–2 weeks after MDT - **N**odular: painful nodules (not macules) - **L**epromatous: only in LL/BL, high bacillary load