Bacteriology: erythema nodosum leprosum: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Bacteriology: erythema nodosum leprosum

Sample item

A 30-year-old man with lepromatous leprosy has taken multidrug therapy for three months. He develops fever, tender red nodules on the limbs, arthralgia and iritis. Biopsy shows a neutrophilic infiltrate with vasculitis. Which mechanism underlies this reaction?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Immune complex deposition (type III hypersensitivity)

Erythema nodosum leprosum, the type 2 reaction, occurs in lepromatous and borderline lepromatous leprosy, often after treatment starts. It is an immune complex reaction with neutrophils and complement, and responds to steroids or thalidomide.

Option by option

  • A. Immune complex deposition (type III hypersensitivity) (correct)

    Correct. ENL is a type III immune complex reaction to released bacillary antigen.

  • B. Rise in cell-mediated immunity (type IV hypersensitivity)

    A type IV upgrading response describes the type 1 (reversal) reaction in borderline disease.

  • C. Spread of bacilli from dapsone resistance

    Resistance would cause slow clinical worsening and relapse and not an acute vasculitic reaction.

  • D. Dapsone-induced haemolysis with methaemoglobinaemia

    Haemolysis would cause anaemia and cyanosis, not tender nodules with vasculitis.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Immune complex deposition (type III hypersensitivity). Erythema nodosum leprosum, the type 2 reaction, occurs in lepromatous and borderline lepromatous leprosy, often after treatment starts.

Why is "Rise in cell-mediated immunity (type IV hypersensitivity)" not the answer?

A type IV upgrading response describes the type 1 (reversal) reaction in borderline disease.

Why is "Spread of bacilli from dapsone resistance" not the answer?

Resistance would cause slow clinical worsening and relapse and not an acute vasculitic reaction.

Why is "Dapsone-induced haemolysis with methaemoglobinaemia" not the answer?

Haemolysis would cause anaemia and cyanosis, not tender nodules with vasculitis.

What concept does this question test?

It tests Bacteriology: erythema nodosum leprosum in Microbiology. It is an immune complex reaction with neutrophils and complement, and responds to steroids or thalidomide.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Bacteriology: erythema nodosum leprosum?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.