Okay, let's tackle this question. The patient is a 40-year-old male with painful flaccid vesicles on the face and oral mucosa that are asymmetrically distributed. The immunofluorescence shows intercellular IgG deposition in the epidermis. I need to figure out the diagnosis.

First, I remember that vesicular lesions with IgG deposits can be pemphigus. Pemphigus vulgaris is a classic one. The intercellular IgG suggests it's targeting desmogleins, which are cadherins in desmosomes. That would cause acantholysis, leading to flaccid blisters. The oral mucosa involvement is common in pemphigus vulgaris. Also, the asymmetric presentation is more typical of pemphigus than pemphigus foliaceus, which is more superficial and less mucosal.

The other options might be bullous pemphigoid, but that usually has linear IgG and IgA deposits along the basement membrane. Lichen planus doesn't have vesicles but rather papules and erosions. Dermatomyositis can have a rash but not vesicles with intercellular IgG. So the correct answer is pemphigus vulgaris.

Wait, let me check. Pemphigus foliaceus also has intercellular IgG but is more superficial and doesn't involve mucosa as much. Since the patient has oral lesions, pemphigus vulgaris is more likely. The key points here are the location (face and mouth), asymmetric distribution, and the immunofluorescence pattern. So the answer should be pemphigus vulgaris.

**Core Concept** The question tests knowledge of autoimmune blistering skin disorders, specifically distinguishing between pemphigus vulgaris and other conditions like pemphigus foliaceus based on clinical presentation and immunofluorescence findings. Intercellular IgG deposition in the epidermis is pathognomonic for pemphigus.

**Why the Correct Answer is Right** Pemphigus vulgaris is characterized by autoantibodies against desmoglein 3 (Dsg3), causing acantholysis (loss of epidermal cell adhesion). This leads to flaccid vesicles and bullae, often involving mucous membranes (oral, nasal) and skin. The asymmetric distribution and intercellular IgG staining on direct immunofluorescence confirm the diagnosis. Oral lesions are more common in pemphigus vulgaris than in pemphigus foliaceus.

**Why Each Wrong Option is Incorrect**
**Option A:** Bullous pemphigoid typically shows linear IgG and C3 deposits at the basement membrane zone, not intercellular.
**Option B:** Lichen planus presents with pruritic, polygonal papules and Wickham striae, not vesicles with IgG deposits.
**Option C:** Dermatomyositis is an inflammatory myopathy with characteristic skin rash (e.g., heliotrope erythema), not vesicular eruptions.

**Clinical Pearl / High-Yield Fact** Remember the "IgG intercellular = pemphigus" rule: Pemphigus vulgaris (mucous membrane involvement) vs. pemphigus foliaceus

✓ Correct Answer: C. Pemphigus vulgaris