Nikolsky's sign is a clinical dermatological sign in which blisters spread easily upon application of horizontal, tangential pressure to the skin. A positive Nikolsky's sign signifies a separation of epithelial cells either from one another or from the basement membrane, which is a layer of connective tissue to which epithelium usually adhered. This occurs in a number of conditions, including but not limited to the potentially fatal autoimmune skin disorder pemphigus vulgaris, staphylococcal scalded skin syndrome and toxic epidermal necrolysis.
To check for the presence of these conditions, as well as certain certain vesicular/bullous diseases (conditions that cause skin blisters to form), such as pemphigus and pemphigoid this test can be administered to ascertain the fragility of the epithelial attachment mechanisms.
One way to perform this test is with a simply pencil. With the eraser side of a pencil down, the pencil is firmly placed on the skin and depressed while twisted. If the patient has one of a number of vesicular/bullous diseases, he or she will test positive for Nikolsky's sign, and a blister will form within a matter of minutes.
Histologic Basis for the Sign
The idea behind this test lies in the histologic properties of certain vesicular/bullous diseases. In these diseases, there are defects in the cell-to-cell attachement mechanisms, and even minute amounts of trauma can elicit a clinical response of a blister formation when the cells are manually detached with the forceful turn of the pencil eraser on the skin. In the case of pemphigus, the pencil twist easily rips the spinous cells apart because they possess defective desmosomes, and in the case of pemphigoid, the hemidesmosomes are defective. Within minutes, a blister will form, and this is pathognomonic, or absolutely indicative, of a vesicular/bullous disease.