**Core Concept**
Erythrasma is a superficial fungal infection caused by Corynebacterium minutissimum, characterized by intertriginous lesions, typically in the groin, axillae, or inframammary regions. It is often associated with warm, humid environments and can be exacerbated by diabetes mellitus or poor hygiene.

**Why the Correct Answer is Right**
The treatment of choice for Erythrasma is topical erythromycin, usually in the form of erythromycin lactobionate or erythromycin stearate. This is because erythromycin is an effective antibiotic against Corynebacterium minutissimum, and its topical application directly targets the causative organism in the affected area. The mechanism of action of erythromycin involves inhibiting protein synthesis by binding to the 50S ribosomal subunit of bacteria, thereby preventing the production of essential proteins.

**Why Each Wrong Option is Incorrect**
**Option A:** Other topical or systemic antibiotics may be used in other types of skin infections, but they are not the treatment of choice for Erythrasma.
**Option B:** Antifungal agents are effective against fungal infections, but Erythrasma is caused by a bacterium, not a fungus.
**Option C:** Corticosteroids can be used to treat skin conditions with inflammation, but they do not address the underlying bacterial infection in Erythrasma.

**Clinical Pearl / High-Yield Fact**
Remember that Erythrasma is often associated with intertriginous areas and can be exacerbated by diabetes mellitus or poor hygiene. It is essential to consider this diagnosis in patients with skin lesions in these areas, especially in the context of other underlying medical conditions.

**Correct Answer:** A. Topical erythromycin.