[Mibelli's porokeratosis gigantea].

This case report deals with the giant form of porokeratosis of Mibelli, porokeratosis Mibelli gigantea. Over the last 40 years, the 55-year-old man concerned had observed a centrifugal expansion of a single hyperkeratotic lesion until it covered the whole of the right hand and forearm. Besides the characteristic histological alterations, we saw capillaries with unusually thickened walls owing to basal lamina multiplication. In the centre of the lesion atrophy of the epidermis and of the corium was visible. These observations indicate an alteration in two germ layers in porokeratosis.