An 18-year-old white male high-school student visits the family physician complaining of a diffuse, painful rash extending from his midthigh to his navel region. In recounting the history of the rash, he indicates that one of his football teammates gave him topical hydrocortisone to treat a minor groin rash. A KOH scraping of the lesion reveals hyaline hyphae and a portion of the scraping is submitted for culture. A schematic of the microscopic observation of the culture is shown below. The most likely etiology is

## **Core Concept**
The patient's symptoms and history suggest a fungal infection, likely **tinea cruris** (jock itch), which is common in warm, moist areas of the body such as the groin. The use of topical hydrocortisone, a corticosteroid, can sometimes exacerbate or modify the presentation of fungal infections, making them more widespread or atypical.

## **Why the Correct Answer is Right**
The description of the KOH scraping showing **hyaline hyphae** points towards a dermatophyte infection, as these are the typical microscopic findings for this type of fungus. Dermatophytes are a group of fungi that infect skin, hair, and nails. The culture and microscopic observation schematic likely revealed features consistent with **Epidermophyton floccosum**, given the context of tinea cruris and the presence of hyaline hyphae. *E. floccosum* is a common cause of tinea cruris and corporis, and it exhibits characteristic features in culture.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without specific details on the organism, it's hard to directly refute, but typically, *Trichophyton* species (like *T. rubrum*) are more common causes of tinea cruris and show different characteristics in culture.
- **Option B:** Similarly, without specifics, it's difficult to directly address, but other fungi might not present with hyaline hyphae or are less commonly associated with this clinical presentation.
- **Option D:** This option might represent another type of fungal infection or a different organism not typically associated with the described clinical scenario and microscopic findings.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the use of **topical corticosteroids** on a presumed fungal infection can lead to a more widespread or severe infection, as seen in this case. This is a common pitfall in the management of dermatologic conditions and emphasizes the importance of obtaining a definitive diagnosis before initiating treatment.

## **Correct Answer: C.**

✓ Correct Answer: A. Epidermophyton floccosum