Porokeratotic eccrine ostial and dermal duct naevus.

With rare exceptions, the presence of cornoid lamellae in skin biopsy specimens is considered diagnostic of porokeratosis. Since the initial descriptions of this condition by Mibelli (1893) and Respighi (1893), there has been debate concerning its relationship to the eccrine sweat duct. This paper describes an epidermal naevus, which pathologically demonstrated gross examples of cornoid lamellae associated exclusively with the eccrine duct and ostia, and which appears to represent a naevus or benign hamartoma of these structures. This entity needs to be clearly differentiated from porokeratosis of Mibelli.