This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blistering disorders, Subject name: Dental
A 85-year-old female developed multiple blisters on trunk and thigh. Nikolsky's sign negative. The lesions came on and off. The most probable diagnosis is: 
Select and explain. 
A. Pemphigus vulgaris, B. Bullous pemphigoid, C. Lichen planus, D. Lepra reaction
B: Bullous pemphigoid
Answer: B: Bullous pemphigoid 
Explanation: Elderly patient, -ve nikolsky sign and multiple blisters on trunk and thigh point towards BP Other features BP AI subepidermal blistering disease. MHC II - HLA-DQ1*0301 is prevalent. Oral mucosal lesions are found rarely (10-40%) Pruritus +/- Nontraumatized blisters heal without scarring Tense blisters-->rupture--> flaccid lesions/ erosions+/- surmounting crust Rx: Mainstay- systemic glucocoicoids -Prednisone, 40 to 60 mg/d.(good response) Azathioprine (1-2 mg/kg/day), Mycophenolate mofetil (20-35mg/kg/day), or Cyclophosphamide (1-2 mg/kg/day)