Proteus syndrome. Ultrastructural study of linear verrucous and depigmented nevi.

Proteus syndrome is a rare hamartomatous disorder characterized by multifocal overgrowths that can involve any structure of the body. Clinical manifestations include macrodactyly, hemihypertrophy, subcutaneous masses, exostosis, cerebroid thickening of palms and soles, and linear skin lesions. About 50 cases have been described, but the ultrastructural features of the linear skin lesions have not been characterized. We describe the clinical, histologic, and ultrastructural findings for a 30-year-old patient who had a mild form of Proteus syndrome with linear lesions characterized by a mixed pattern of hyperkeratosis and depigmentation. Light microscopy of the linear nevus showed acanthosis and hyperorthokeratosis. Electron microscopy revealed extensive vacuolation at the interface between melanocytes and keratinocytes, with large aggregations of densely packed granules in the intercellular space. Melanocytes showed only slight degenerative changes. An immunohistochemical study of the expression of epidermal growth factor receptors revealed no significant abnormalities.