You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is 'Bulla spread sign' is seen in which of the following condition? and explain in detail?
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.