Koebner phenomenon
The Koebner phenomenon or Köbner phenomenon (, ), also called the Koebner response or the isomorphic response, attributed to Heinrich Köbner, is the appearance of skin lesions 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 toxicodendron dermatitis (a dermatitis caused by a genus of plants including poison ivy). Warts and molluscum contagiosum lesions can be spread in linear patterns by self-scratching ("auto-inoculation"). Toxicodendron dermatitis lesions are often linear from brushing up against the plant. Causes of the Koebner phenomenon that are secondary to scratching rather than an infective or chemical cause include vitiligo, psoriasis, lichen planus, lichen nitidus, pityriasis rubra pilaris, and keratosis follicularis (Darier disease). Definition The Koebner phenomenon describes skin lesions which appear at the site of injury. It is seen in: Psoriasis Pityriasis rubra pilaris Lichen planus Flat warts Lichen nitidus Vitiligo Lichen sclerosus Elastosis perforans serpiginosa Kaposi sarcoma Necrobiosis lipoidica Lupus Juvenile Idiopathic Arthritis Still disease Cutaneous leishmaniasis Post kala azar dermal leishmaniasis Eruptive xanthomas A similar response occurs in pyoderma gangrenosum and Behcet's syndrome, and is referred to as pathergy.