Mycology: tinea nigra: 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 · Mycology: tinea nigra

Sample item

A 10-year-old returning from a tropical coastal holiday has a painless, non-scaly, brown-black macule on the palm that looks like a silver nitrate stain. KOH mount shows brown septate hyphae and budding yeast cells. Which organism is responsible?

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

The answer and the reasoning

D. Hortaea werneckii

Tinea nigra is a superficial infection of the stratum corneum by the dematiaceous fungus Hortaea werneckii. It causes a painless dark patch, usually on the palm, and is often mistaken for melanoma, but KOH examination shows pigmented hyphae.

Option by option

  • A. Sporothrix schenckii

    S. schenckii causes subcutaneous nodules along lymphatics with cigar-shaped yeasts.

  • B. Malassezia furfur

    Malassezia causes pityriasis versicolor with fine scaling and hypopigmentation or hyperpigmentation on the trunk.

  • C. Trichophyton rubrum

    T. rubrum causes scaly inflammatory tinea with hyaline hyphae.

  • D. Hortaea werneckii (correct)

    Correct. Brown hyphae and yeast cells on a palmar dark macule indicate H. werneckii.

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 D, Hortaea werneckii. Tinea nigra is a superficial infection of the stratum corneum by the dematiaceous fungus Hortaea werneckii.

Why is "Sporothrix schenckii" not the answer?

S. schenckii causes subcutaneous nodules along lymphatics with cigar-shaped yeasts.

Why is "Malassezia furfur" not the answer?

Malassezia causes pityriasis versicolor with fine scaling and hypopigmentation or hyperpigmentation on the trunk.

Why is "Trichophyton rubrum" not the answer?

T. rubrum causes scaly inflammatory tinea with hyaline hyphae.

What concept does this question test?

It tests Mycology: tinea nigra in Microbiology. It causes a painless dark patch, usually on the palm, and is often mistaken for melanoma, but KOH examination shows pigmented hyphae.

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 Mycology: tinea nigra?

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.