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 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).

The Koebner phenomenon describes skin lesions which appear at the site of injury. It is seen in:

• Psoriasis
• Pityriasis rubra pilaris
• Lichen planus
• Lichen nitidus
• Vitiligo
• Lichen sclerosus
• Elastosis perforans serpiginosa
• Kaposi sarcoma
• Necrobiosis lipoidica
• Systemic Lupus Erythematosus

A similar response occurs in pyoderma gangrenosum and Adamantiades-Behcet's syndrome, and is referred to as pathergy.

Warts and molluscum contagiosum are often listed as causing a Koebner reaction, but this is by direct inoculation of viral particles.