A 74-year-old man presents with a 6-week history of pruritic urticarial plaques on his flexural areas, followed by the development of tense, fluid-filled bullae with intact roofs on an erythematous base. Oral examination reveals no mucosal involvement. The clinical presentation shown in the diagram, particularly the feature marked **D** (elderly patient with minimal mucosal involvement), is most consistent with which diagnosis?

Explanation

## Why Bullous pemphigoid is right Bullous pemphigoid is the most common autoimmune blistering disease in the elderly (mean onset >70 years), presenting with pruritic urticarial plaques followed by tense bullae with intact roofs on flexural areas. The key clinical feature marked **D** — elderly patient with minimal or no mucosal involvement — is a critical distinguishing feature of BP. The disease results from autoantibodies against BP180 (collagen XVII, a major hemidesmosomal protein) and BP230, causing a subepidermal split at the dermoepidermal junction. The bullae are tense (not flaccid) because the epidermal roof remains intact. Nikolsky sign is negative, reflecting the subepidermal location with an intact basement membrane. This presentation in an elderly patient without significant mucosal disease is pathognomonic for BP (Harrison 21e Ch 71). ## Why each distractor is wrong - **Pemphigus vulgaris**: While also an autoimmune blistering disease, PV is characterized by intraepidermal acantholysis, flaccid bullae with fragile roofs, and prominent mucosal involvement (often the first manifestation). The absence of mucosal disease and the presence of tense bullae with intact roofs make this diagnosis unlikely. PV shows intercellular IgG deposition, not linear IgG at the basement membrane zone. - **Dermatitis herpetiformis**: This condition presents with intensely pruritic vesicles and papules predominantly on extensor surfaces (elbows, knees, buttocks), not flexural areas. It is strongly associated with celiac disease and shows granular IgA deposition at dermal papillae, not linear IgG at the basement membrane. The clinical distribution and immunofluorescence pattern differ significantly from this case. - **Linear IgA bullous dermatosis**: Although this condition also presents with subepidermal bullae and linear IgA at the basement membrane zone, it is often drug-induced (classically by vancomycin) and does not show the characteristic elderly demographic or the specific anti-BP180/BP230 antibody profile. The clinical context and immunological findings distinguish it from BP. **High-Yield:** Bullous pemphigoid in the elderly = tense bullae + flexural distribution + minimal mucosal involvement + negative Nikolsky sign + linear IgG at basement membrane zone on direct immunofluorescence. [cite: Harrison 21e Ch 71]