Positive Nikolsky sign occurs when the dermis separates from the epidermis due to a serve
immune mediated reaction.

Occurss in  SJS, TEN, staphylococcal scalded skin, and pemphigus vulgaris.

Stevens-Johnson syndrome denotes patients with skin necrosis that involves between 10%
to 30% of the body surface, while TEN typically has greater than 30% of body surface area.