A patient has a dry, scaly, erythematous penis. Skin scales stained with calcofluor white show fluorescent blue-white yeasts and a few pseudohyphae. What is the causative agent of this dermatophytic look-alike?

Okay, let's tackle this question. The patient has symptoms of a dry, scaly, erythematous penis. The key part here is that the skin scales tested with calcofluor white show fluorescent blue-white yeasts and pseudohyphae. The question is asking about the causative agent that mimics a dermatophyte infection but isn't one.

First, I need to recall what calcofluor white does. It's a fluorescent stain that binds to chitin in fungal cell walls, making them visible under UV light. So, the presence of yeasts and pseudohyphae suggests a yeast infection. Dermatophytes are molds, not yeasts, so this is a look-alike, meaning it's a yeast that's causing a condition similar to a dermatophytosis.

Common yeast infections include candidiasis. Candida species are yeasts that can form pseudohyphae. So, the likely culprit here is Candida. Specifically, Candida albicans is a common cause of genital yeast infections. The symptoms described—dry, scaly, erythematous—align with a candidal infection, which can sometimes be mistaken for a dermatophyte infection because both can cause red, scaly rashes. However, the key difference is the type of organism seen under the microscope.

Now, looking at the options (even though they aren't listed here), the correct answer would be the one referring to Candida. The other options might include dermatophytes like Trichophyton, which are molds and would show hyphae without pseudohyphae. Another possible distractor could be Malassezia, which causes pityrosporum infections, but those typically present differently, maybe with more seborrheic areas. Also, other yeasts like Cryptococcus might be considered, but they don't form pseudohyphae. So, the correct answer is Candida, specifically C. albicans.

The clinical pearl here is that calcofluor white can help differentiate between yeast and dermatophyte infections. Remembering that pseudohyphae indicate yeast (like Candida) versus hyphae in dermatophytes is crucial. Also, the fact that the infection is a "look-alike" points towards a yeast mimicking a dermatophyte infection, which is a classic scenario for candidiasis.

**Core Concept**
This question tests identification of a fungal infection mimicking dermatophytosis. Calcofluor white staining highlights chitin in fungal cell walls, distinguishing yeasts (Candida) from dermatophytes (Trichophyton spp.), which lack pseudohyphae.

**Why the Correct Answer is Right**
Candida species (typically *Candida albicans*) cause genital candidiasis, presenting as erythematous, scaly lesions. Calcofluor white staining reveals **yeasts with pseudohyphae**, a hallmark of Candida. Unlike dermatophytes, Candida lacks true hyphae and forms pseudohyphae, confirming a yeast infection.

**Why Each Wrong Option is Incorrect**
**Option A:** Dermatophytes (e.g., *Trichophyton*) produce hyphae, not pseudohyphae, and stain as septate, branching hyphae under

✓ Correct Answer: A. Candida