ENL reaction in leprosy — DTM&H MCQ

Correct answer: C — Type 2 ENL reaction — thalidomide or prednisolone

The correct answer is C, Type 2 ENL reaction, treated with thalidomide or prednisolone. Erythema nodosum leprosum (ENL) is an immune complex mediated, neutrophilic reaction that occurs in multibacillary (lepromatous or borderline lepromatous) leprosy, typically within the first two years of treatment. The clinical picture of tender erythematous nodules on the limbs, fever and arthralgia/arthritis is classical for ENL, distinguishing it from the granulomatous, cell mediated type 1 reaction. Thalidomide is highly effective for moderate to severe ENL in non-pregnant patients due to its anti TNF alpha and immunomodulatory action, with prednisolone used when thalidomide is contraindicated (pregnancy, women of childbearing potential without adequate contraception) or unavailable. Multidrug therapy for leprosy should be continued throughout the reaction. Why the other options are wrong: A. Type 1 reversal reaction: this presents with inflammation and swelling of existing skin lesions and new lesions, often with neuritis, in borderline patients undergoing an immune shift, not with systemic nodules, fever and joint pain typical of ENL. D. Jarisch-Herxheimer: this is a cytokine release reaction after starting antimicrobials for spirochaetal infections (eg syphilis, leptospirosis), presenting with fever and rigors shortly after the first dose, unrelated to leprosy treatment at 3 months. E. Drug hypersensitivity, stop all drugs: there is no rash pattern or timing here suggestive of a drug allergy, and stopping leprosy multidrug therapy is not indicated as continuing treatment alongside reaction management is standard practice. B. Lucio phenomenon: this is a distinct, severe vasculitic/thrombotic reaction seen almost exclusively in diffuse lepromatous leprosy (Lucio leprosy), causing necrotic ulcers, not tender nodules with arthritis. Key point: Tender nodules plus fever plus arthritis at 3 months of multibacillary leprosy treatment is ENL (type 2 reaction), managed with thalidomide (or prednisolone if contraindicated) while continuing multidrug therapy.

Reference: Hospital for Tropical Diseases, UCLH / London School of Hygiene and Tropical Medicine: Patel C, De Barros B, Walker SL, 'Localised erythema nodosum leprosum: a rare entity managed with thalidomide', Skin Health and Disease, 2024, https://pmc.ncbi.nlm.nih.gov/articles/PMC10988736/