A 42-year-old woman with borderline tuberculoid leprosy on MDT develops sudden inflammation of existing skin lesions and acute neuritis of the ulnar nerve 2 months after starting treatment. There is no fever or systemic symptoms. What is the drug of choice for this condition?

Explanation

## Type 1 Lepra Reaction (Reversal Reaction) ### Clinical Diagnosis This patient presents with **Type 1 lepra reaction (reversal reaction)**, characterized by: - Inflammation of **existing skin lesions** (not new nodules) - **Acute neuritis** (often single nerve involvement) - **No systemic symptoms** (no fever, no constitutional symptoms) - Occurs in **borderline forms** (BT, BL) of leprosy - Timing: during or shortly after starting MDT **Key Point:** Type 1 is a delayed-type hypersensitivity (DTH) reaction mediated by CD4+ T cells responding to mycobacterial antigens. It reflects improving cell-mediated immunity during effective chemotherapy. ### Immunological Basis | Reaction Type | Immune Mechanism | Timing | Lesion Pattern | Systemic Symptoms | |---|---|---|---|---| | **Type 1 (RR)** | DTH (CD4+ T cells) | During/after MDT start | Inflammation of existing lesions | Absent | | **Type 2 (ENL)** | Immune complex (IC) | During/after MDT start | New painful nodules | Present (fever, malaise) | ### Drug of Choice: Prednisolone **High-Yield:** Prednisolone is the first-line drug for Type 1 lepra reaction because it suppresses DTH by reducing T-cell activation and pro-inflammatory cytokine production (IL-2, IFN-γ). **Dosing Regimen:** - **Initial:** 0.5–1 mg/kg/day (typically 40–80 mg/day) - **Duration:** Taper over 12–16 weeks - **Monitoring:** Clinical improvement in neuritis and lesion inflammation; gradual reduction in dose **Clinical Pearl:** Unlike ENL, Type 1 reaction does NOT require thalidomide as first-line. Thalidomide is ineffective for Type 1 because the pathology is DTH-mediated, not TNF-α-driven immune complex deposition. ### Treatment Algorithm ```mermaid flowchart TD A[Lepra Reaction Suspected]:::outcome --> B{Type 1 or Type 2?}:::decision B -->|Type 1<br/>Existing lesion inflammation<br/>No fever| C[Prednisolone 0.5-1 mg/kg/day]:::action B -->|Type 2<br/>New nodules<br/>Fever + systemic| D[Prednisolone ± Thalidomide]:::action C --> E[Taper over 12-16 weeks]:::action D --> F[Prednisolone taper;<br/>Thalidomide if recurrent]:::action E --> G[Resolution of neuritis<br/>and lesion inflammation]:::outcome F --> G ``` **Warning:** Do not confuse Type 1 with Type 2. The absence of fever and systemic symptoms, combined with inflammation of existing lesions in a borderline form, is diagnostic of Type 1. Thalidomide is NOT indicated for Type 1.