Phacomatosis pigmentokeratotica: a patient with the rare melanocytic-epidermal twin nevus syndrome.

We describe a 10-year-old girl affected with a speckled lentiginous nevus and an epidermal nevus of the organoid type on corresponding parts of the body. On histopathological examination, the lesions showed epidermal hyperpigmentation and melanocytic hyperplasia on the one hand and verrucous epidermal acanthosis with sebaceous hyperplasia on the other hand. Except for a minor deviation of the spine, the patient had no obvious extracutaneous symptoms. Happle et al. have recently interpreted the rare co-occurrence of these two types of nevi in spatial proximity as an example of twin spotting in human skin and proposed the name 'phacomatosis pigmentokeratotica'. In most cases, additional skeletal or neurological anomalies are found. These are dissimilar from the extracutaneous symptoms of the sebaceous nevus syndrome, from which phacomatosis pigmentokeratotica should be distinguished. Molecular studies are needed to prove the concept of twin spotting and to reveal a link to the extracutaneous manifestations.