Extensive speckled lentiginous nevus associated with giant congenital melanocytic nevus: an unusual example of twin spotting?

A 15-year-old boy had an unusual combination of giant congenital melanocytic nevus on his back and a large speckled lentiginous nevus arranged in a checkerboard pattern on the dorsal and lateral aspects of his trunk. The two pigmentary nevi showed distinguishing features both clinically and histopathologically. The speckled lentiginous nevus was not noted at birth but became visible during childhood. We hypothesize that this uncommon co-occurrence may represent a further example of twin spotting and may be categorized as a new, distinct type of phacomatosis.