Fungal infections: Wood's lamp fluorescence: 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.

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Dermatology · Fungal infections: Wood's lamp fluorescence

Sample item

A child with scaly patchy alopecia shows bright green fluorescence of hairs under Wood's lamp. Which organism is most likely?

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

The answer and the reasoning

C. Microsporum canis

Microsporum species cause an ectothrix infection with bright green fluorescence due to pteridine. T. tonsurans, T. violaceum and T. rubrum do not fluoresce, while T. schoenleinii gives a dull greenish glow.

Option by option

  • A. Trichophyton rubrum

    T. rubrum rarely infects the scalp and is non-fluorescent.

  • B. Trichophyton tonsurans

    T. tonsurans is endothrix and does not fluoresce.

  • C. Microsporum canis (correct)

    Correct. M. canis gives bright green fluorescence.

  • D. Trichophyton violaceum

    T. violaceum is endothrix and does not fluoresce.

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 Dermatology question

What is the answer to this Dermatology question?

The best answer is C, Microsporum canis. Microsporum species cause an ectothrix infection with bright green fluorescence due to pteridine.

Why is "Trichophyton rubrum" not the answer?

T. rubrum rarely infects the scalp and is non-fluorescent.

Why is "Trichophyton tonsurans" not the answer?

T. tonsurans is endothrix and does not fluoresce.

Why is "Trichophyton violaceum" not the answer?

T. violaceum is endothrix and does not fluoresce.

What concept does this question test?

It tests Fungal infections: Wood's lamp fluorescence in Dermatology. T. tonsurans, T. violaceum and T. rubrum do not fluoresce, while T. schoenleinii gives a dull greenish glow.

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 Fungal infections: Wood's lamp fluorescence?

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.