The immune system mistakenly regards the cells in the skin and mucous membranes as foreign and attacks them.
2. A distinctive group of skin and mucous membrane diseases, characterized by successive skin eruptions of crops of bullae (large blisters or vesicles which are serum-filled blisters formed in or beneath the skin).3. An acute or chronic autoimmune disease principally of adults but sometimes found in children, characterized by an occurrence of successive crops of bullae that appear suddenly on apparently normal skin and disappear, leaving pigmented spots.
A characteristic sign is a positive Nikolsky's sign: when pressure is applied to an area as if trying to push the skin parallel to the surface, the skin will detach from the lower layers.
Nikolsky's sign is also described as a peculiar vulnerability of the skin in pemphigus vulgaris; where the apparently normal epidermis may be separated at the basal layer and rubbed off when pressed with a sliding motion.
Pyotr Nikolsky (1858-1940) was a Russian dermatologist.
A diagnostic feature wherein apparently normal epithelium may be rubbed off with pressure.
One simple way to perform this test is with a 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 (blister)/bullous (bump filled with fluid) diseases, he or she will test positive for Nikolsky's sign, and a blister will form within a matter of minutes.
The 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 attachment mechanisms, and even very small 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 (specialised structure that attaches an epithelial cell, or outside layer of a cell, to the basement membrane beneath it) are defective.
Within minutes, a blister will form, and this is pathognomonic, or absolutely indicative, of a vesicular/bullous disease.