Mycology: tinea incognito: 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.

Try it

Microbiology · Mycology: tinea incognito

Sample item

A 30-year-old man has extensive, itchy, ring-shaped lesions on the groin and trunk that have lost their raised scaly border after months of using an over-the-counter steroid and antifungal combination cream. What is the most appropriate initial investigation?

APatch testing with standard allergensBTzanck smear from a lesionCKOH mount of scrapings from the lesion edgeDWood's lamp examination of the lesions

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

The answer and the reasoning

C. KOH mount of scrapings from the lesion edge

Topical steroids suppress inflammation and alter the appearance of dermatophytosis, producing tinea incognito with extensive spread. Direct microscopy of scrapings in 10 to 20% potassium hydroxide shows septate hyphae and confirms the diagnosis, and culture on Sabouraud agar identifies the species. Treatment is with oral antifungals once steroid use stops.

Option by option

A. Patch testing with standard allergens
Patch testing assesses contact allergy and does not diagnose fungal infection.
B. Tzanck smear from a lesion
A Tzanck smear detects multinucleated giant cells in herpesvirus infection.
C. KOH mount of scrapings from the lesion edge (correct)
Scrapings in KOH show hyphae quickly and cheaply and confirm dermatophytosis.
D. Wood's lamp examination of the lesions
Most dermatophytes of the body and groin do not fluoresce, so Wood's lamp is of little value here.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is C, KOH mount of scrapings from the lesion edge. Topical steroids suppress inflammation and alter the appearance of dermatophytosis, producing tinea incognito with extensive spread.

Why is "Patch testing with standard allergens" not the answer?

Patch testing assesses contact allergy and does not diagnose fungal infection.

Why is "Tzanck smear from a lesion" not the answer?

A Tzanck smear detects multinucleated giant cells in herpesvirus infection.

Why is "Wood's lamp examination of the lesions" not the answer?

Most dermatophytes of the body and groin do not fluoresce, so Wood's lamp is of little value here.

What concept does this question test?

It tests Mycology: tinea incognito in Microbiology. Direct microscopy of scrapings in 10 to 20% potassium hydroxide shows septate hyphae and confirms the diagnosis, and culture on Sabouraud agar identifies the species. Treatment is with oral antifungals once steroid use stops.

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 incognito?

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.