Background: The epidermal nevus syndromes include different diseases that have the common feature of mosaicism. One of these has been recently identified and named phacomatosis pigmentokeratotica, in analogy to phacomatosis pigmentovascularis. It is characterized by an organoid nevus with sebaceous differentiation, a speckled-lentiginous nevus, and other associated anomalies. It has been hypothesized that this syndrome is caused by a particular genetic mechanism known as the twin-spot phenomenon. Observations: We describe 3 patients manifesting an association of organoid nevus showing sebaceous differentiation and speckled-lentiginous nevus with associated anomalies and update the neurologic findings of a previously described patient. Hemiatrophy seems to be a common finding in all cases; hyperpathia; dysesthesia, and hyperhidrosis, as well as other neurologic defects, may be present. Conclusions: The findings in these patients allowed us to better delineate this syndrome. Further studies are needed to elucidate the underlying genetic detect. At present, however, the hypothesis that best explains this phenotype is twin spotting. Clinical recognition of this syndrome can contribute to the classification of the epidermal nevus syndromes and give insight into unusual genetic mechanisms occurring in humans.
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