Paired hairless and hairy nevi: a further example of twin spotting?

Whorled hairless nevus of the scalp, linear hyperpigmentation, and telangiectatic nevi of the lower limbs: a novel variant of the "phacomatosis complex"

The term "phacomatosis" refers to a growing number of sporadic genetic skin disorders characterized by the combination of two or more different nevi and possibly resulting from non-allelic twin spotting. While phacomatosis pigmentovascularis (PPV) and pigmentokeratotica represent the most common patterns, some patients do not fit with either condition and are temporarily classified as unique phenotypes. We report on an 8-year-old boy with striking right hemihypoplasia, resulting in limb asymmetry and fixed dislocation of right hip. Skin on the affected side showed three distinct nevi: (i) A whorled, hairless nevus of the scalp in close proximity with (ii) epidermal hyperpigmentation following lines of Blaschko on the neck and right upper limb, and (iii) multiple telangiectatic nevi of the right lower limb and hemiscrotum. Didymosis atricho-melanotica was proposed for the combination of adjacent patchy congenital alopecia and linear hyperpigmentation, while phacomatosis atricho-pigmento-vascularis appears to define the entire cutaneous phenotype, thus implying the involvement of three neighboring loci influencing the development of distinct constituents of the skin. Given the striking asymmetry of the observed phenotype, the effect of mosaicism (either genomic or functional) for a mutation in a single gene with pleiotropic action and influenced by the lateralization pattern of early development cannot be excluded.

Cutis tricolor parvimaculata: a distinct neurocutaneous syndrome?

An 11-year-old girl had multiple, disseminated, rather small café-au-lait macules and hypochromic spots involving the neck, the trunk and the legs. In part, the two types of macules showed a spatial proximity, suggesting didymosis (twin spotting). The term cutis tricolor has been proposed to describe congenital paired hyperchromic and hypochromic macules on a background of intermediate skin. Because the spots present in this case were much smaller than those described in previous cases of cutis tricolor, we here propose the distinguishing term 'cutis tricolor parvimaculata'. The underlying gene locus may be a hot spot for postzygotic recombinations, giving rise to multiple twin spots. Moreover, the girl had developed seizures from the age of 10 years, and a large oligodendroglioma involving the left frontal lobe was found. A causal relationship between the cutaneous phenotype and the cerebral tumor is unproven but likely. The skin lesions were reminiscent of a disorder described by Westerhof et al. in 1978 under the term 'hereditary congenital hypopigmented and hyperpigmented macules'. So far, however, it is not clear whether cutis tricolor parvimaculata is identical with or different from this disorder.