A 36-year-old factory worker developed itchy, annular scaly plaques in both groins. Application of a coicosteroid ointment led to temporary relief but the plaques continued to extend at the periphery. The most likely diagnosis is:

**Core Concept**
The patient's symptoms, including itchy, annular scaly plaques in the groin area, suggest an inflammatory skin condition that is resistant to topical corticosteroid treatment. This clinical presentation is characteristic of a chronic, autoimmune skin disorder.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with **discoid lupus erythematosus (DLE)**, a type of cutaneous lupus erythematosus. DLE is characterized by the formation of coin-shaped, scaly plaques that can appear on sun-exposed areas, including the face, ears, and extremities. The patient's failure to respond to topical corticosteroids suggests a more severe, autoimmune-mediated process.

* **Option A:** Psoriasis is incorrect because it typically presents with erythematous, scaly plaques on the elbows, knees, and scalp, rather than the groin area.
* **Option B:** Contact dermatitis is incorrect because it is a localized, allergic reaction to a specific substance, and the patient's symptoms are more widespread and chronic.
* **Option C:** Seborrheic dermatitis is incorrect because it typically presents with greasy, yellowish scales on the scalp, face, and torso, rather than the groin area.

**Clinical Pearl / High-Yield Fact**
DLE can be distinguished from other skin conditions by its characteristic, coin-shaped lesions and the presence of mucin deposits in the dermis, which can be visualized using immunofluorescence microscopy.

**Correct Answer:** C. Discoid lupus erythematosus.

✓ Correct Answer: D. Tinea cruris