Nevoid Skin Disorders

Abstract

Abstract This group includes X-linked skin disorders, some autosomal non-nevi, and mosaic manifestations of common, acquired skin disorders with a polygenic background Among the X-linked genodermatoses, some phenotyopes exclusively occur in women because the underlying gene is acting as a lethal factor for male embryos. Affected female embryos survive by the mechanism of lyonization. This group of disorders includes incontinentia pigmenti, focal dermal hypoplasia, Conradi-Hunermann-Happle syndrome, MIDAS syndrome, and oral-facial digital syndrome type I. Another X-linked, male-lethal trait is Aicardi syndrome that cannot be categorized as a genodermatosis because constant cutaneous features are lacking, although a unilateral hairy bridge between eyebrow and scalp hair (“trichogephyrosis”) was noted in one case. – In X-linked genodermatoses caused by non-lethal mutations, male patients are diffusely and severely affected, whereas female carriers usually show a Blaschko-linear pattern of lyonization. Such phenotypes include Christ-Siemens-Touraine syndrome, X-linked dyskeratosis congenita, Menkes syndrome, IFAP syndrome, and the reticulate pigmentary disorder of Partington. By contrast, women heterozygous for X-linked generalized hypertrichosis tend to show a checkerboard pattern of lyonization. In the X-linked albinism-deafness syndrome, the arrangement of depigmented areas as noted in affected females is so far unclassifiable, whereas their irides show a definite sectorial pattern of hypopigmentation. Autosomal non-nevi: Some skin disorders look like nevi but are definitely no nevi, either because they represent benign neoplastic lesions or because someone has called them nevi without reason. The lesions of syringocystadenoma papilliferum tend to be arranged in a linear, nevus-like pattern, but they are benign neoplasias, which is why they do not fulfil the criteria of a nevus. Similarly, the hemangiomas and enchondromas of Maffucci syndrome are distributed in a mosaic arrangement, but they are likewise neoplastic lesions. The same holds for the segmentally arranged basaloid follicular hamartomas of Happle-Tinschert syndrome, and for the subcutaneous lipomas of hemihyperplasia-multiple lipomata syndrome. – The salmon patch (“Unna’s nevus”, “median nevus flammeus”) is no nevus because the criterion of mosaicism is lacking. – “White sponge nevus of the oral mucosa” is an absurd term. The symmetric lesions of this autosomal dominant trait may better be called “white sponge hyperplasia of the mucosa”. – The term “basal cell nevus” is incorrect because it denotes neoplastic skin lesions. Moreover, the term is ambiguous because it has been used to describe quite different disorders such as the disseminated basal cell carcinomas of Gorlin syndrome, or a mosaic manifestation of Gorlin syndrome, or hereditary nonsyndromic basal cell carcinomas, or the basaloid follicular hamartomas of Happle-Tinschert syndrome. – Finally, “blue rubber bleb nevus syndrome” is a misnomer because these vascular lesions are benign neoplasias. Hence, the term “blue rubber bleb angiomatosis” is more appropriate. Acquired skin disorders: Some of these diseases occur in a mosaic arrangement but do not fulfill the criteria of a nevus because they tend to resolve spontaneously after some time. Examples are lichen striatus (including “blaschkitis”), lichen aureus, linear Grover disease, and linear juvenile xanthogranuloma. – On the other hand, numerous common skin disorders with a polygenic background sometimes show a linear or otherwise segmental distribution, either as an isolated nevoid manifestation or being superimposed on the nonsegmental phenotype. The segmental lesions would originate either from an early event of allelic loss at one of the predisposing loci, or from a postzygotic new mutation at an additional locus predisposing to the disorder. Clinical examples suggesting a superimposed segmental involvement include psoriasis vulgaris, pustular psoriasis, atopic dermatitis, lichen planus, lichen planopilaris, lichen nitidus, acne vulgaris, discoid lupus erythematosis, lupus erythematosus profundus, subacute lupus erythematosus, systemic lupus erythematosus, dermatomyositis, pemphigus vulgaris, bullous pemphigoid, graft-versus-host disease, morphea, granuloma annulare, erythema multiforme, common drug eruption, fixed drug eruption, lateralized exanthema of childhood, vitiligo, and cherry angiomas.