Dear Editor,
I read with interest the outstanding case recently published in the Turkish Journal of Dermatology.1 Poddar et al.1 reported eruptive vellus hair cysts (EVHC) arranged in a segmental distribution, namely in S-shaped bands respecting the midline. The authors define such a pattern as “zosteriform”. Instead, the lesions seem to clearly follow Blaschko lines, which are a known phenotypical pattern of cutaneous mosaicism and the only one followed by mosaic conditions affecting the pilosebaceous unit (e.g. nevus comedonicus). Only two cases of lateralized EVHC have been reported previously,2,3 but their distribution of lesions is not compatible with segmental mosaicism. Hence, this is the first reported instance of mosaic EVHC.
EVHC can arise sporadically or may be inherited in an autosomal dominant fashion with incomplete penetrance;4 the genetic defect has not yet been identified. In autosomal dominant skin disorders, heterozygosity for a postzygotic new mutation is defined as type 1 segmental mosaicism.5 Hence, the case of Poddar et al.1 allows the inclusion of EVHC among the ever-growing list of conditions known to possibly manifest as type 1 segmental mosaicism.
