Random Dermatology MCQ - Bullous pemphigoid

A 60-year-old man presents with tense bullae on erythematous urticated plaques on his trunk and flexures. Direct immunofluorescence of perilesional skin shows linear deposition of IgG and C3 along the basement membrane zone. ELISA testing is positive for antibodies against the NC16A domain of BP180. Which of the following is the most likely diagnosis?

A) Pemphigus vulgaris
B) Bullous pemphigoid
C) Epidermolysis bullosa acquisita
D) Linear IgA disease
E) Dermatitis herpetiformis

Correct Answer: B) Bullous pemphigoid

Explanation

This patient has bullous pemphigoid (BP), the most common autoimmune blistering disorder.

Key Diagnostic Features:

1. Clinical:

   • Tense bullae on urticated, erythematous skin (contrasts with flaccid blisters of pemphigus).

   • Predilection for flexures and trunk.

   • Intense pruritus is common.

2. Immunopathology:

   • Direct immunofluorescence (DIF): Linear IgG and C3 along the basement membrane zone (gold standard).

   • Serology: Antibodies against BP180 (type XVII collagen) and less commonly BP230. The NC16A domain of BP180 is the major immunogenic region.

3. Histopathology:

   • Subepidermal blister with eosinophil-rich infiltrate.

Why Not Other Options?

• (A) Pemphigus vulgaris: DIF shows intercellular IgG/C3 deposition; antibodies against desmoglein 3.

• (C) Epidermolysis bullosa acquisita: DIF may be identical, but serology shows antibodies against type VII collagen; blisters are trauma-induced and heal with scarring.

• (D) Linear IgA disease: DIF shows linear IgA deposition along BMZ.

• (E) Dermatitis herpetiformis: DIF shows granular IgA deposition in dermal papillae; associated with celiac disease.

Management:

• First-line: Potent topical corticosteroids (e.g., clobetasol) for limited disease; systemic corticosteroids for extensive disease.

• Steroid-sparing agents: Doxycycline, dapsone, methotrexate, or rituximab.

Prognosis: Self-limited course in many patients, but can be chronic with relapses.