A young boy presented with a lesion over his right buttock, which had peripheral scaling with central scarring. The investigation of choice would be?
**Core Concept**
The young boy's presentation of a lesion with peripheral scaling and central scarring is suggestive of a skin condition known as discoid lupus erythematosus (DLE), a form of cutaneous lupus erythematosus. This condition is characterized by chronic inflammation and scarring in the skin, often with a predilection for the face, scalp, and extremities, but can also affect other areas like the buttocks.
**Why the Correct Answer is Right**
The investigation of choice for DLE is a biopsy of the affected skin lesion. This allows for histopathological examination, which is essential for diagnosing DLE. The biopsy will typically show characteristic changes such as basal cell degeneration, mucin deposition, and a band-like inflammatory infiltrate at the dermo-epidermal junction. These findings help differentiate DLE from other skin conditions that may present with similar clinical features.
**Why Each Wrong Option is Incorrect**
* **Option A:** A punch biopsy is indeed a suitable method for obtaining a skin sample, but it is not the investigation of choice for DLE. Other methods like shave biopsy or excisional biopsy can also be used.
* **Option B:** A Wood's lamp examination is useful for diagnosing conditions like vitiligo, but it is not the investigation of choice for DLE.
* **Option C:** A potassium hydroxide (KOH) preparation is used to diagnose fungal infections, which is not relevant to the diagnosis of DLE.
**Clinical Pearl / High-Yield Fact**
When considering a skin biopsy, it's essential to take a sample that includes the characteristic peripheral scaling and central scarring seen in DLE, as this will increase the diagnostic yield.
**Correct Answer:** C. A biopsy of the affected skin lesion.