Communicable diseases: leprosy reactions: practice question

A PSM 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.

Try it

PSM · Communicable diseases: leprosy reactions

Sample item

A 30-year-old man with lepromatous leprosy has been on multidrug therapy for 3 months. He now develops fever, malaise and crops of tender erythematous nodules over his limbs. What is the underlying mechanism of this reaction?

AAllergic reaction to rifampicinBImmune complex deposition (type III hypersensitivity) in erythema nodosum leprosumCRelapse due to rifampicin-resistant bacilliDDelayed-type (type IV) hypersensitivity in a type 1 reaction

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

The answer and the reasoning

B. Immune complex deposition (type III hypersensitivity) in erythema nodosum leprosum

Erythema nodosum leprosum is a type 2 lepra reaction seen mainly in lepromatous and borderline lepromatous disease, often after starting treatment as bacillary antigens are released. It is mediated by immune complexes and is treated with analgesics, corticosteroids or thalidomide, while multidrug therapy is continued. A type 1 reaction occurs in borderline disease with inflamed existing skin lesions and neuritis.

Option by option

A. Allergic reaction to rifampicin
A drug allergy would present with rash or fever early on, not typical crops of tender nodules in lepromatous leprosy.
B. Immune complex deposition (type III hypersensitivity) in erythema nodosum leprosum (correct)
Correct. ENL is a type III immune complex reaction.
C. Relapse due to rifampicin-resistant bacilli
Relapse would show new infiltrated lesions over time and is not a cause of acute reaction in the first months of therapy.
D. Delayed-type (type IV) hypersensitivity in a type 1 reaction
Delayed hypersensitivity underlies type 1 reactions, which show inflamed existing patches rather than new tender nodules.

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.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, Immune complex deposition (type III hypersensitivity) in erythema nodosum leprosum. Erythema nodosum leprosum is a type 2 lepra reaction seen mainly in lepromatous and borderline lepromatous disease, often after starting treatment as bacillary antigens are released.

Why is "Allergic reaction to rifampicin" not the answer?

A drug allergy would present with rash or fever early on, not typical crops of tender nodules in lepromatous leprosy.

Why is "Relapse due to rifampicin-resistant bacilli" not the answer?

Relapse would show new infiltrated lesions over time and is not a cause of acute reaction in the first months of therapy.

Why is "Delayed-type (type IV) hypersensitivity in a type 1 reaction" not the answer?

Delayed hypersensitivity underlies type 1 reactions, which show inflamed existing patches rather than new tender nodules.

What concept does this question test?

It tests Communicable diseases: leprosy reactions in PSM. It is mediated by immune complexes and is treated with analgesics, corticosteroids or thalidomide, while multidrug therapy is continued. A type 1 reaction occurs in borderline disease with inflamed existing skin lesions and neuritis.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Communicable diseases: leprosy reactions?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.