Sexually transmitted infections: practice question

A Dermatology 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

Dermatology · Sexually transmitted infections

Sample item

A 28-year-old man has a non-itchy coppery macular rash that involves the palms and soles, and moist flat-topped plaques in the groin. Serum VDRL is non-reactive. What is the best explanation and next step?

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

The answer and the reasoning

A. Prozone phenomenon; repeat the test on diluted serum

In secondary syphilis the antibody titre can be so high that it blocks flocculation, producing a false-negative non-treponemal test (prozone phenomenon). Diluting the serum restores reactivity, and a treponemal test such as TPHA can confirm the diagnosis.

Option by option

  • A. Prozone phenomenon; repeat the test on diluted serum (correct)

    Correct. Very high antibody levels can mask the reaction until the serum is diluted.

  • B. Syphilis is excluded because a non-reactive VDRL rules it out at every stage

    A negative test does not exclude syphilis, particularly when the clinical picture is classic and a prozone effect is possible.

  • C. Serological tests become reactive only in tertiary syphilis

    Serological tests are usually strongly reactive in the secondary stage, not only in tertiary disease.

  • D. Antibodies appear late, so the test is expected to be negative; repeat after 3 months

    Antibody levels are at their highest in the secondary stage, so a delayed antibody response does not explain the result.

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.

More Dermatology questions

Questions about this Dermatology question

What is the answer to this Dermatology question?

The best answer is A, Prozone phenomenon; repeat the test on diluted serum. In secondary syphilis the antibody titre can be so high that it blocks flocculation, producing a false-negative non-treponemal test (prozone phenomenon).

Why is "Syphilis is excluded because a non-reactive VDRL rules it out at ever…" not the answer?

A negative test does not exclude syphilis, particularly when the clinical picture is classic and a prozone effect is possible.

Why is "Serological tests become reactive only in tertiary syphilis" not the answer?

Serological tests are usually strongly reactive in the secondary stage, not only in tertiary disease.

Why is "Antibodies appear late, so the test is expected to be negative; repea…" not the answer?

Antibody levels are at their highest in the secondary stage, so a delayed antibody response does not explain the result.

What concept does this question test?

It tests Sexually transmitted infections in Dermatology. Diluting the serum restores reactivity, and a treponemal test such as TPHA can confirm the diagnosis.

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 Sexually transmitted infections?

Learn each condition by its primary lesion, site and signature sign. Then use the flashcards and the other Dermatology 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.