True isomorphic phenomenon is not seen in: March 2005

Ans. A: Lichen Sclerosis The Koebner phenomenon is the development of isomorphic pathologic lesions in the traumatized uninvolved skin of patients who have cutaneous diseases. It refers to the fact that in persons with ceain skin diseases, especially psoriasis, trauma (scratches, surgical incisions/ injury) is followed by new lesions in the traumatized but otherwise normal skin, and these new lesions are clinically and histopathologically identical to those in the diseased skin. Type of Koebner phenomenon: Boyd and Neldner have classified all repoed cases of Koebner phenomenon into four different groups: True isomorphic phenomenon-There appear to be three disease processes that display the true isomorphic response of Koebner: psoriasis, lichen planus and vitiligo; Pseudoisomorphic phenomenon the Koebner phenomenon seen in infectious diseases, e.g. was, molluscum contagiosum and Behcet's disease and pyoderma gangrenosum; Occasionally occurring isomorphic phenomenon-In this category, diseases occasionally localize to sites of trauma, e.g. cancer (gastric, testicular or mammary), Darier's disease, erythema multiforme, Hailey-Hailey disease, Kaposi's sarcoma, Kyrle's disease, lichen sclerosus et atrophicus, pellagra, perforating folliculitis, reactive perforating collagenosis, and Questionable isomorphic phenomenon -There are many conditions that have been associated with the Koebner phenomenon, many of which are single case repos. This includes: anaphylactoid purpura, bullous pemphigoid, dermatitis herpetiformis, discoid lupus erythematosus, eczema, erythrokeratoderma variabilis, keratoacanthoma, lichen amyloidosis, lichen nitidus, multicentric reticulohistiocytosis, nevocytic nevi, pityriasis rubra pilaris, porokeratosis of Mibelli, uicaria pigmentosa, uicarial eruption of Still's disease, telangiectasia macularis eruptive perstans, transient acantholyic dermatosis, vasculitis, and xanthoma eruptivum.