Koebner phenomenon



The Koebner phenomenon, also called the "Koebner response" or the "isomorphic response", refers to skin lesions appearing on lines of trauma. The Koebner phenomenon may result from either a linear exposure or irritation. Conditions demonstrating linear lesions after a linear exposure to a causative agent include: molluscum contagiosum, warts and rhus dermatitis (a dermatitis caused by poison ivy). Warts and molluscum contagiosum lesions can be spread in linear patterns by self-scratching ("auto-inoculation"). Rhus dermatitis lesions can appears linear either from brushing up against the plant or spreading of the urushiol by scratching. In contrast to exposure causes of the Koebner phenomenon, the following disorders do not have an infective or chemical cause, instead, the irritation of trauma itself can act as a co-factor in producing linear patterns: vitiligo, psoriasis, lichen planus, lichen nitidus, pityriasis rubra pilaris, and keratosis follicularis (Darier disease).

The Koebner phenomenon was named after a rather eccentric, renowned German dermatologist, Heinrich Koebner (1838-1904). Koebner is best known for his work in mycology. Here is one story to illustrating his intense nature: in a medical meeting he proudly exhibited on his arms and chest three different fungus infections which he self-inoculated in order to prove the infectiousness of the organisms he was studying. The Koebner phenomenon was the generalized term applied to his discovery that on psoriasis patients, new lesions often appear on lines of trauma which are often linear.

The linear arrangement of skin lesions in the Koebner phenomenon can be contrasted to both lines of Blaschko and dermatomal distributions. Blaschko lines follow embryotic cell migration patterns and are seen in some mosaic genetic disorders such as incontinentia pigmenti and pigment mosaicism. Dermatomal distributions are lines on the skin surface following major nerves. The rash caused by herpes zoster (Shingles) follows such dermatomal lines.