Erythema nodosum leprosum (ENL) is classified as which type of lepra reaction and occurs most commonly in which leprosy classification?

Explanation

## Erythema Nodosum Leprosum (ENL) — Type 2 Lepra Reaction **Key Point:** ENL is a **Type 2 lepra reaction** (immune complex–mediated, Type III hypersensitivity) that occurs predominantly in **lepromatous (LL) and borderline lepromatous (BL)** forms of leprosy. ### Pathophysiology 1. **Immune Mechanism:** Deposition of circulating immune complexes (antigen-antibody) in skin, nerves, eyes, and kidneys 2. **Antigen Source:** Mycobacterial antigens from dead bacilli (especially during early treatment) 3. **Antibody Involvement:** High titers of IgG and IgM against *M. leprae* 4. **Complement Activation:** Leads to inflammation and tissue damage ### Why LL and BL? - **High bacillary load** → abundant mycobacterial antigens - **Defective CMI** → cannot clear bacilli efficiently → persistent antigen source - **High antibody titers** → abundant immune complexes form - **TT and BT:** Low bacillary load, strong CMI → insufficient antigen for IC formation ### Timing and Triggers - Usually occurs **during or shortly after** starting treatment (first 6 months) - Triggered by **bacterial death** and antigen release - Can occur in untreated patients with high bacillary load ### Clinical Features of ENL - Painful nodules, papules, pustules (not in existing lesions) - Fever, systemic symptoms - Neuritis, iritis, orchitis, glomerulonephritis - Histology: **neutrophilic infiltration**, vasculitis, IC deposition **High-Yield:** **Type 2 = LL/BL; Type 1 = BT/BL.** ENL is the hallmark of **high bacillary load** leprosy forms. **Mnemonic:** **ENL = Exudative Nodular Lesions = Lepromatous.** Type **2** occurs in **L**epromatous (remember: 2 L's in "lepromatous").