Patchy dermal hypoplasia as a characteristic feature of Proteus syndrome.

BACKGROUND The diagnostic criteria of Proteus syndrome include various lesions of localized overgrowth such as digital gigantism, hemihyperplasia with unilateral macrocephaly, epidermal nevus, and mesodermal hamartomas such as lipoma, lymphangioma, hemangioma, or fibroma. Hyperplasia of the plantar dermal tissue may result in a characteristic cerebriform appearance. However, hypoplastic lesions involving various tissues such as subcutaneous fat or muscles also may be observed in this syndrome. This paradoxical phenomenon has so far been underestimated, and the presence of circumscribed lesions of dermal hypoplasia has been entirely ignored. OBSERVATIONS We report 4 cases of Proteus syndrome associated with large patches of dermal hypoplasia, resulting in a more prominent appearance of venous vasculature. CONCLUSIONS Patchy dermal hypoplasia appears to be a characteristic feature within the spectrum of Proteus syndrome. The anomaly should not be confused with partial lipohypoplasia that may likewise be associated with this multisystem birth defect. From a review of the literature, we conclude that patchy dermal hypoplasia may have occurred in several previous cases. In the future, recognition of this cutaneous anomaly may help to establish the diagnosis in otherwise doubtful cases. To explain the coexistence of lesions of dermal hyperplasia and hypoplasia, we propose the genetic concept of "twin spotting." At the gene locus of Proteus syndrome the embryo would carry 1 allele giving rise to dermal overgrowth, whereas the corresponding allele would be responsible for a diminished proliferation of cutaneous fibroblasts. Somatic recombination may result in 2 different populations of cells homozygous for either allele.