A 28-year-old woman with borderline tuberculoid leprosy (BT) is started on MDT (rifampicin, dapsone, clofazimine) for 12 months. After 3 months of therapy, she develops severe erythematous nodules, fever (38.5°C), and painful swelling of the left ulnar nerve. Her ESR is elevated at 95 mm/hr. Skin biopsy shows granulomatous inflammation with increased bacillary load in previously treated lesions. She has been compliant with treatment. What is the most likely diagnosis?

Explanation

## Diagnosis: Type 1 Lepra Reaction (Reversal Reaction) ### Clinical Presentation Analysis **Key Point:** The patient presents with acute inflammation of existing lepromatous lesions and nerves during active MDT in a BT (borderline tuberculoid) patient—this is the hallmark of Type 1 lepra reaction (reversal reaction). ### Differential Features of Lepra Reactions | Feature | Type 1 (Reversal) | Type 2 (ENL) | |---------|-------------------|---------------| | **Timing** | During or shortly after MDT (weeks to months) | Usually after 6+ months of therapy; can occur years later | | **Leprosy type** | BT, BL (borderline forms) | LL, BL (lepromatous end) | | **Immune mechanism** | Cell-mediated (delayed-type hypersensitivity) | Immune complex (Type III) | | **Lesion changes** | Existing lesions become inflamed, erythematous; may ulcerate | New tender nodules, iritis, neuritis | | **Bacillary load** | May increase transiently in lesions | Usually low (post-treatment) | | **Systemic signs** | Fever, nerve tenderness/swelling | Fever, arthralgia, iritis, orchitis | | **ESR/CRP** | Elevated | Markedly elevated | | **Histology** | Granulomatous inflammation (Type IV) | Vasculitis, neutrophilic infiltrate | | **Treatment** | Corticosteroids; continue MDT | Thalidomide (gold standard); corticosteroids; continue MDT | ### Why Type 1 Reaction Here? 1. **Timing:** 3 months into therapy—classic window for reversal reaction (can occur weeks to months after starting MDT) 2. **Leprosy type:** BT (borderline tuberculoid) is prone to Type 1 reactions 3. **Clinical signs:** Inflammation of existing lesions + nerve swelling (neuritis) + fever 4. **Histology clue:** "Granulomatous inflammation with increased bacillary load in previously treated lesions"—indicates immune activation against bacilli in existing lesions 5. **Compliance:** Patient is compliant, ruling out drug resistance **Clinical Pearl:** Type 1 lepra reaction represents a shift toward better cell-mediated immunity (Th1 response) triggered by antigen release from killed bacilli. It is a sign of immune reconstitution, not treatment failure. The transient increase in bacillary load in lesions reflects immune activation, not resistance. **High-Yield:** Type 1 reactions occur in borderline forms (BT, BL); Type 2 reactions occur in lepromatous forms (LL, BL). This patient's BT status makes Type 1 far more likely. ### Management - Continue MDT without interruption - High-dose corticosteroids (prednisolone 0.5–1 mg/kg/day, tapered over 8–12 weeks) - NSAIDs for pain and inflammation - Nerve protection (splinting if motor involvement) - Monitor for nerve damage **Mnemonic: TYPE 1 = **T**ransient, **Y**ield to steroids, **P**romotes immunity, **E**xisting lesions inflame; **1** = **1**-month to **1**-year onset** [cite:Park 26e Ch 8]