<prompt> A 85 yr old female developed multiple blisters on trunk and thighs. Nikolsky;s sign is negative. The lesions came on and off. The most probable diagnosis isLichen planusPemphigus vulgarisBullous pemphigoidLepra reaction  <response>: Bullous Pemphigoid BP Most common autoimmune bullous disorder with chronic nature; typically in patients over 60 Autoantigen: - BPAG2 collagen XVII: 180 kDa NC16A domain, transmembrane hemidesmosomal protein BPAG1: 230 kDa, cytoplasmic plaque protein Clinical features:- Often presents with initial uicarial lesions which evolve into large, tense bullae over medial thighs, groin, abdomen, and legs; - pruritus initially with subsequent tenderness; no constitutional symptoms unless extensive disease; 10-35 with oral involvement Drug-induced:- Furosemide, NSAIDs, phenacetin, PCN-derivatives, gold, potassium iodide, captopril, enalapril, D-penicillamine, sulfasalazine Histology:- Subepidermal bulla with eosinophils and lymphocytes in papillary dermis, - neutrophils. Investigations:- DIF: linear C3 and IgG latter weaker at BMZ IIF: in 60-80; IIF on salt-split skin SSS shows binding to epidermal side of split roof of blister Treatment:- Oralcoicosteroid, steroid-sparing agent azathioprine, mycophenolate mofetil, etc, TCN nicotinamide, dapsone; good prognosis. Ref:- Sima Jain; pg num:- 130 