**Core Concept:** Blister formation in the skin is primarily due to damage to the basal layer of the epidermis, which is supported by the basement membrane. Inflammatory cells and antibody deposits are usually seen in autoimmune blistering disorders.

**Why the Correct Answer is Right:** In this case, the most likely diagnosis is **Dermatomyositis (DM)**. DM is a rare autoimmune disorder characterized by muscle weakness, skin rash, and inflammation affecting the dermal-epidermal junction, resulting in bullae formation. The absence of inflammatory cells and antibody deposits in the skin biopsy excludes other autoimmune blistering disorders like bullous pemphigoid (BP), pemphigus vulgaris (PV), and pemphigus foliaceus (PF).

**Why Each Wrong Option is Incorrect:**

A. Bullous pemphigoid (BP): BP is an autoimmune blistering disorder characterized by subepidermal blisters, prominent neutrophils, and IgG deposits in the dermo-epidermal junction.

B. Pemphigus vulgaris (PV): PV is another autoimmune blistering disorder featuring subepidermal blisters, IgG and C3 deposits in the subepidermal zone, and characteristic mucosal involvement.

C. Pemphigus foliaceus (PF): PF is a subtype of pemphigus characterized by superficial bullae, IgG and C3 deposits in the epidermal basement membrane zone, and follicular involvement.

**Clinical Pearl:** Dermatomyositis should be suspected in patients presenting with muscle weakness, rash, and blisters, especially when the clinical findings are not consistent with other autoimmune blistering disorders. In such cases, a skin biopsy is crucial for confirming the diagnosis.

**Correct Answer:** Dermatomyositis (DM)