A 32-year-old man from rural Maharashtra presents with a 6-month history of hypopigmented macules on his face, trunk, and extremities with loss of sensation in the affected areas. Slit-skin smear examination shows 4+ acid-fast bacilli (AFB). He is diagnosed with lepromatous leprosy and started on multidrug therapy (MDT). During the second week of treatment, he develops fever, painful nodules, and worsening of existing skin lesions. What is the most likely diagnosis of this acute complication?

Explanation

## Lepra Reaction Type 2 (Erythema Nodosum Leprosum) ### Clinical Presentation **Key Point:** ENL is an immune complex-mediated reaction (Type III hypersensitivity) that occurs in lepromatous and borderline lepromatous leprosy patients, typically 2 weeks to 2 years after starting MDT (most commonly within the first 3 months). The patient's presentation—fever, painful nodules, and acute worsening of skin lesions during early MDT—is pathognomonic for ENL. This is distinct from reversal reaction, which occurs *before* or *during* early treatment and is mediated by cell-mediated immunity (Type IV). ### Pathophysiology 1. **Antigen-antibody complex formation:** As bacillary load decreases with MDT, immune complexes form from released mycobacterial antigens and circulating IgG antibodies. 2. **Complement activation:** These complexes deposit in skin, nerves, eyes, testes, and kidneys, triggering inflammation. 3. **Timing:** ENL typically emerges when bacillary load is still high but immune response is mounting—hence the early presentation in this patient. ### Differential: Lepra Reaction Type 1 vs Type 2 | Feature | Type 1 (Reversal) | Type 2 (ENL) | |---------|-------------------|---------------| | **Mechanism** | Cell-mediated (Type IV) | Immune complex (Type III) | | **Timing** | Before/during early treatment | 2 weeks–2 years after MDT start | | **Leprosy type** | Borderline forms (BT, BL, BB) | LL, BL | | **Lesions** | Existing lesions swell, become red | New painful nodules, systemic symptoms | | **Systemic signs** | Minimal | Fever, constitutional symptoms | | **Neuritis** | Common | Rare | | **Treatment** | Corticosteroids | Corticosteroids + thalidomide | **High-Yield:** ENL is characterized by fever + painful nodules + systemic symptoms appearing *after* MDT initiation; reversal reaction shows inflammation of *existing* lesions *before/during* early treatment. ### Management of ENL 1. **Corticosteroids:** Prednisolone 0.5–1 mg/kg/day, tapered over weeks to months. 2. **Thalidomide:** 100–300 mg/day (gold standard for ENL; contraindicated in pregnancy due to severe teratogenicity). 3. **Continue MDT:** Do not stop antileprotic drugs; ENL is a sign of immune recovery. 4. **Supportive care:** NSAIDs for pain, ophthalmologic monitoring if eyes involved. **Clinical Pearl:** Thalidomide is highly effective in ENL because it suppresses TNF-α production, a key mediator of Type III hypersensitivity. However, it is teratogenic and requires strict contraception in women of childbearing age. ### Complications of ENL - Iridocyclitis and blindness - Neuritis and nerve damage - Orchitis and testicular atrophy - Glomerulonephritis - Hepatitis **Mnemonic:** **ENL = Early, Nodules, Late** — Early presentation (weeks) after MDT, Nodules (painful), Late-stage leprosy (LL/BL).