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 is

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