'Bulla spread sign' is seen in which of the following condition?

Pemphigus vulgaris is associated with positive Nikolsky sign and Asboe- Hansen sign or Bullae spread sign. In positive bullae spread sign, pressing the top of existing bullae will lead to spread of bullae to adjacent normal appearing skin. Positive Nikolsky sign refers to shearing of the epidermis by exeing lateral pressure on the normal skin adjacent to an active blister. Pemphigus vulgaris is an acquired chronic disease in which blisters develop on normal appearing skin and mucous membrane. In this condition the pemphigus antibodies attach to extracellular domain of desmoglein and interfere with its attachment to similar domains on other cells reducing cell cell adherence. It is characterised by the development of flaccid clear blister which rupture and evolve into an inflamed erosion. Ref: Blistering Skin Diseases By Lawrence S. Chan page 26.