Erythema Nodosum Leprosum
On this page
Direct answer
Erythema nodosum leprosum (ENL) is a type 2 lepra reaction, an immune complex mediated inflammatory episode that occurs in patients with lepromatous or borderline lepromatous leprosy. It produces crops of tender red nodules on the limbs, usually with fever and systemic upset, and it can damage nerves and the eyes. Treatment is with systemic corticosteroids, with thalidomide or clofazimine used as steroid-sparing agents, and multidrug therapy continues throughout.
What you must remember
- Reaction type: ENL is a type 2 lepra reaction, distinct from the type 1 reversal reactions that affect borderline disease.
- Patients affected: it occurs mainly in LL and BL leprosy, where the bacillary load is high.
- Timing: it may appear before, during or after multidrug therapy, so a reaction does not by itself mean treatment failure.
- Mechanism: antigen-antibody immune complexes deposit in the skin and blood vessels, a type III hypersensitivity process.
- Skin lesions: crops of tender, erythematous, raised subcutaneous nodules, mainly on the arms and legs, that fade and leave pigmentation.
- Systemic features: fever, malaise, arthralgia, lymphadenitis, neuritis, iritis and orchitis.
- First-line treatment: systemic prednisolone for the acute episode, tapered as the reaction settles.
- Steroid-sparing agents: clofazimine and thalidomide, with thalidomide teratogenic and strictly avoided in pregnancy.
A stepwise approach to an ENL episode
A patient with lepromatous disease presents with painful red nodules and fever. The priority is to recognise the episode as a reaction rather than infection or relapse, and to start treatment without delay.
- Recognise the reaction: Crops of tender nodules with fever in a known leprosy patient point to ENL, and the nodules are typically symmetrical on the limbs.
- Screen for complications: Check for neuritis, iritis, orchitis, lymphadenitis and any loss of nerve function, since these features need urgent care.
- Exclude mimics: Consider erythema nodosum from other causes, cellulitis and drug reactions, and check the patient's recent drug history.
- Start systemic steroids: Prednisolone is the standard first-line agent for moderate to severe ENL, with the dose tapered over the following weeks as the nodules settle.
- Add a steroid-sparing agent: Clofazimine or thalidomide is used for recurrent or steroid-dependent disease, and thalidomide needs strict pregnancy precautions before it is prescribed.
- Continue multidrug therapy: The episode is never a reason to stop MDT, because the bacilli still need treatment while the reaction is managed separately.
- Protect the eyes and nerves: Follow the patient closely for nerve damage and ophthalmic complications, and refer urgently for iritis or new weakness.
Where the exam tries to catch you
Most traps involve mislabelling the reaction type or misjudging the safety of the drugs used to treat it.
- Trap: calling ENL a type 1 reaction Correct: ENL is a type 2 reaction driven by immune complexes, whereas reversal reactions are type 1 and occur in borderline disease.
- Trap: giving thalidomide to a woman of child-bearing potential without precautions Correct: thalidomide is teratogenic and must not be used in pregnancy, so pregnancy testing and contraception come first.
- Trap: stopping MDT during an ENL episode Correct: multidrug therapy continues, since the reaction is treated separately from the underlying infection.
- Trap: reading ENL as drug resistance Correct: ENL is an immune reaction that can occur during effective therapy, so it does not signal treatment failure.
Frequently asked questions
Which leprosy types are most prone to erythema nodosum leprosum?
Erythema nodosum leprosum occurs mainly in lepromatous (LL) and borderline lepromatous (BL) leprosy, where bacillary loads are high. It is a type 2 reaction, so it is not a typical feature of tuberculoid leprosy.
How is erythema nodosum leprosum treated?
Erythema nodosum leprosum is treated with systemic corticosteroids such as prednisolone for the acute episode. Thalidomide and clofazimine serve as steroid-sparing agents, and multidrug therapy continues throughout the reaction.
Why must thalidomide be avoided in pregnancy in erythema nodosum leprosum?
Thalidomide is a teratogen that causes severe fetal malformations, so it is contraindicated in pregnancy. Women of child-bearing potential need pregnancy testing and reliable contraception before thalidomide is started for erythema nodosum leprosum.
What is the histological picture of erythema nodosum leprosum?
Erythema nodosum leprosum shows a neutrophilic infiltrate with vasculitis in the dermis and subcutaneous fat, typically a lobular or mixed panniculitis. This differs from the purely septal panniculitis of ordinary erythema nodosum and from the granulomatous pattern of tuberculoid leprosy.
Can erythema nodosum leprosum cause permanent nerve damage?
Erythema nodosum leprosum can cause acute neuritis, which may lead to permanent nerve damage if it is not treated promptly. Early steroid treatment and close nerve monitoring reduce this risk in patients with erythema nodosum leprosum.