Koebner phenomenon

Koebner phenomenon


The Koebner phenomenon, also called the Koebner
response or the isomorphic response, attributed to Heinrich Koebner, 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). 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, Systemic Lupus Erythematosus,
Juvenile Idiopathic Arthritis, Still disease and Cutaneous leishmaniasis. A similar response occurs in pyoderma gangrenosum
and Adamantiades-Behcet’s syndrome, and is referred to as pathergy. Rarely Koebner phenomenon has been reported
as a mechanism of acute myeloid leukemia dissemination. Warts and molluscum contagiosum are often
listed as causing a Koebner reaction, but this is by direct inoculation of viral particles. 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 the distribution of spinal nerve roots. The rash caused by herpes zoster (Shingles)
follows such dermatomal lines. The Koebner phenomenon was named after the
rather eccentric but renowned German dermatologist Heinrich Koebner (1838–1904). Koebner is best known for his work in mycology. His intense nature is illustrated by the following:
in a medical meeting, he proudly exhibited on his arms and chest three different fungus
infections, which he had self-inoculated, in order to prove the infectiousness of the
organisms he was studying. The Koebner phenomenon is the generalized
term applied to his discovery that on psoriasis patients, new lesions often appear along lines
of trauma.

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