Okay, let's tackle this question. The patient is a young male with scaly truncal lesions, genital lesions, and oral 'lace-like' lesions. The key here is to figure out which condition fits all these symptoms.

First, I remember that psoriasis can present with scaly patches, often on the trunk. But the oral lesions being lace-like make me think of something else. Wait, lichen planus has those white, lacy oral lesions called Wickham striae. Also, genital involvement is common in lichen planus. So maybe the answer is lichen planus.

Let me check the other options. Psoriasis can have scaly lesions but not the lace-like oral ones. Eczema usually doesn't have that specific oral finding. Contact dermatitis might have similar lesions but again, not the lace-like pattern. So the most likely diagnosis is lichen planus. The clinical pearl here is to remember the classic triad: skin, genital, and oral lesions with Wickham striae. That's a high-yield fact for exams.

**Core Concept**
This question assesses the differential diagnosis of dermatological conditions with characteristic cutaneous and mucosal presentations. Lichen planus is a chronic inflammatory disorder that classically presents with pruritic, violaceous, polygonal papules on the skin, along with mucosal involvement (oral or genital) and Wickham striae (lace-like white lines).

**Why the Correct Answer is Right**
Lichen planus is characterized by the triad of **skin lesions** (scaly, flat-topped, purple papules on the trunk), **genital lesions** (erythematous, erosive, or scaly patches), and **oral lesions** (Wickham striae—distinctive lace-like, white, reticulated lines). The pathogenesis involves T-cell-mediated immune attack on basal keratinocytes, leading to a lichenoid inflammatory infiltrate. The oral and genital mucosa are common sites due to their high cell turnover and immune surveillance.

**Why Each Wrong Option is Incorrect**
**Option A:** *Psoriasis* presents with silvery scales and erythematous plaques but lacks lace-like oral lesions.
**Option B:** *Eczema* typically shows erythema, vesicles, and lichenification but not Wickham striae or genital involvement.
**Option C:** *Contact dermatitis* causes erythema and blisters due to allergen exposure, but oral lesions are rare.

**Clinical Pearl / High-Yield Fact**
Remember the **"Lichen Planus Triad"**: skin (truncal scaly lesions), **genital** (erythematous/erosive), and **oral** (Wickham striae). Oral findings are often the first clue and are pathognomonic. Avoid confusing with lichenoid reactions (e.g., drug-induced), which mimic lichen planus but resolve upon removing the trigger.

**Correct Answer: C. Lichen Planus**

✓ Correct Answer: A. Lichen planus