A middle aged man presented with multiple flaccid bullae and oral mucosal lesions. The most likely finding would be:

Erosions on mucous membranes and skin and flaccid blisters on skin are clinical features of pemphigus vulgaris. Pemphigus vulgaris (PV) is an autoimmune disease, characterized by acantholysis, induced by deposition of IgG autoantibodies in the intercellular area of epidermis. PV typically begins on mucosal surfaces and often progresses to involve the skin. PV is characterized by fragile, flaccid blisters that rupture to produce extensive denudation of mucous membranes and skin. PV typically involves the mouth, scalp, face, neck, axilla, groin, and trunk. Erosions can be induced in normal-appearing skin distant from active lesions by pressure or mechanical shear force. This phenomenon is known as the Nikolsky sign. On direct immunofluorescence in perilesional skin, it shows intercellular deposits of IgG giving a fishnet appearance. For detection of circulating IgG antibodies, indirect immunofluorescence is used. Ref: Illustrated Synopsis Of Dermatology & Sexually Transmitted Diseases By Khanna, 3rd edition, Page 63-66.