Bullous Pemphigoid — Tense Bullae Elderly

A 68-year-old man presents with a 6-week history of pruritic lesions on his flexural surfaces and lower abdomen. On examination, the lesions marked **A** in the diagram are firm, intact, and do not rupture easily when gentle pressure is applied. The surrounding skin shows erythema and urticarial changes. Nikolsky sign is negative. A biopsy of perilesional normal skin shows linear IgG and C3 deposition along the basement membrane zone. Which of the following is the most likely diagnosis?