**Question:** An 82-year-old man presents with a 1 and a half-week history of severe pruritus and eczema. His past medical history includes atopic dermatitis, thyroid disease, and multiple sclerosis. On physical examination, he has dozens of 1-2 cm tense bullae and several erosions over his upper and lower extremities. His oral mucosa is not involved. Nikolsky sign is negative. A skin biopsy is taken and anti-BP 180 is detected in his blood. A potent topical steroid is prescribed. The most likely diagnosis is

A. Systemic sclerosis
B. Graft versus host disease (GvHD)
C. Sweet syndrome
D. Goodpasture syndrome

**Correct Answer:**

**Core Concept:** Bullous pemphigoid (BP) is a rare autoimmune bullous dermatosis characterized by the presence of autoantibodies directed against the hemidesmosomal proteins BP180 and BP230. It primarily affects the elderly and presents with tense bullae and erosions, typically on extensor surfaces.

**Why the Correct Answer is Right:**

The correct answer is **B. Graft versus host disease (GvHD)**. The patient presents with tense bullae and erosions, which is a typical feature of BP. Additionally, the presence of autoantibodies against BP180 (anti-BP180) confirms the diagnosis.

**Why Other Options are Incorrect:**

A. **Systemic sclerosis (SSc)** typically presents with scleroderma and Raynaud's phenomenon, not bullae and erosions. Autoantibodies against BP180 are not a hallmark of SSc.

C. **Sweet syndrome (SS)** presents with abrupt onset of acute febrile neutrophilic dermatosis, usually associated with infection or malignancy. The absence of fever, neutrophilia, and a history of recent infection rules out Sweet syndrome.

D. **Goodpasture syndrome (GPS)** is characterized by hematuria, pulmonary fibrosis, and renal failure, which are not present in this case. Also, anti-BP180 antibodies are not a hallmark of Goodpasture syndrome.

**Clinical Pearls:**

- Bullous pemphigoid (BP) is a common autoimmune bullous dermatosis affecting the elderly population.
- The presence of autoantibodies against BP180 is crucial for the diagnosis of BP.
- Autoantibodies against BP180 differentiate BP from other bullous dermatoses, such as Sweet syndrome, Goodpasture syndrome, and systemic sclerosis.