**Question:** A 30-yr-old male had severely itchy papulovesicular lesions over the extremities, knees, elbows and buttocks for one year. Direct immunofluorescence staining of lesions showed IgA deposition in papillary dermis in granular pattern. The most probable diagnosis is:

A. Pemphigus vulgaris
B. Lichen planus
C. Polymorphous light eruption
D. Eczema

**Correct Answer:**

A. Pemphigus vulgaris

**Core Concept:**

Direct immunofluorescence (DIF) staining is a technique used in dermatopathology to assess the deposition of immunoglobulins (IgG, IgA, IgM, IgE, C3, and fibrinogen) and/or complements (C3 and C4) in the skin lesions. This helps to identify the specific antibodies involved in the disease process. In Pemphigus vulgaris, autoantibodies (IgG) are directed against desmoglein-1 and desmoglein-3 proteins, which are desmosomal cadherins present in the epidermis. These antibodies cause intraepidermal blistering and result in the clinical features of Pemphigus vulgaris.

**Why the Correct Answer is Right:**

In the given scenario, the presence of granular IgA deposition in the papillary dermis is a characteristic feature of Pemphigus vulgaris. The granular pattern of IgA deposition is not seen in other conditions. The other options are:

**Option A (Pemphigus vulgaris):**
- Direct immunofluorescence shows granular deposition of IgG in the epidermis
- Clinical features include tense bullae, erosions, and scaling
- Autoantibodies target desmoglein-1 and desmoglein-3 proteins

**Option B (Lichen Planus):**
- Direct immunofluorescence shows granular deposition of IgA and IgG in the dermo-epidermal junction
- Clinical features include polygonal, violaceous, and tense bullae are absent

**Option C (Polymorphous Light Eruption):**
- Direct immunofluorescence shows granular deposition of IgA, IgG, IgM, and C3 in the dermo-epidermal junction
- Clinical features include photosensitive papules and plaques, with or without tense bullae

**Option D (Eczema):**
- Direct immunofluorescence shows granular deposition of IgA, IgM, IgG, and C3 in the dermo-epidermal junction
- Clinical features include dry, red, and itchy papules and plaques

**Why the Correct Answer is Right:**

Pemphigus vulgaris is characterized by autoantibodies targeting desmoglein-1 and desmoglein-3 proteins in the epidermis, leading to intraepidermal blister formation and epidermal necrolysis. The presence of granular deposition of IgA in the dermo-epidermal junction is typical of Lichen Planus