**Core Concept**
The patient's presentation of itchy annular scaly plaques in both groins suggests a chronic dermatological condition characterized by peripheral extension, despite initial response to topical corticosteroids. This condition is often associated with chronic inflammation and immune system dysregulation.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with **tinea cruris**, also known as jock itch, caused by a fungal infection (typically *Trichophyton rubrum* or *Epidermophyton floccosum*). The peripheral extension of the plaques despite initial response to topical corticosteroids is characteristic of this condition. The use of corticosteroids may initially suppress the inflammatory response, but the fungal infection persists, leading to continued plaque extension.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the patient's presentation. **Psoriasis** is a chronic autoimmune condition characterized by well-demarcated erythematous scaly plaques, but it typically involves the elbows, knees, and scalp, not the groin area.

**Option B:** **Contact dermatitis** can cause itchy plaques, but it is typically associated with a history of exposure to a specific allergen or irritant, which is not mentioned in the scenario.

**Option C:** **Seborrheic dermatitis** can cause scaly plaques, but it is typically characterized by a greasy, yellowish scale and involves the scalp, face, and torso, not the groin area.

**Clinical Pearl / High-Yield Fact**
Topical corticosteroids can worsen fungal infections by suppressing the body's immune response, leading to persistent infection and continued plaque extension.

**Correct Answer:** D.