**Core Concept**
Bullous pemphigoid is a chronic autoimmune skin disease characterized by the formation of blisters. The condition results from the production of autoantibodies against the basement membrane zone of the skin, leading to inflammation and blister formation. Effective management of bullous pemphigoid involves suppressing the autoimmune response and reducing inflammation.

**Why the Correct Answer is Right**
High-dose prednisone (50-100 mg/day) is the most appropriate initial treatment for bullous pemphigoid. This is because the condition is characterized by significant inflammation and blister formation, which requires aggressive suppression with high-dose corticosteroids. Prednisone works by inhibiting the transcription of inflammatory genes, leading to a reduction in the production of pro-inflammatory cytokines and a decrease in inflammation. High-dose prednisone also helps to reduce the production of autoantibodies against the basement membrane zone.

**Why Each Wrong Option is Incorrect**
**Option A:** Plasmapheresis is a treatment option for severe autoimmune diseases, but it is not typically used as the initial treatment for bullous pemphigoid. Plasmapheresis involves the removal of autoantibodies from the blood, but it is usually reserved for patients who do not respond to corticosteroids or other treatments.

**Option B:** Low-dose prednisone (10-20 mg/day) may be used as maintenance therapy in patients with stable bullous pemphigoid, but it is not sufficient to control the inflammation and blister formation associated with the initial presentation of the disease.

**Option D:** Azathioprine is an immunosuppressive medication that may be used in combination with corticosteroids to treat bullous pemphigoid, but it is not typically used as the initial treatment due to its slower onset of action and potential side effects.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the initial dose of prednisone for bullous pemphigoid should be high enough to control the inflammation and blister formation, but not so high that it leads to significant side effects. The goal is to find the optimal balance between efficacy and safety.

**✓ Correct Answer: C. high-dose prednisone (50-100 mg/day)**