We describe a patient who developed a pigmented plaque on the anterior aspect of his right knee clinically mimicking angiokeratoma circumscriptum or malignant melanoma. Histopathological examination demonstrated a multinodular hemosiderotic dermatofibroma in which the cellular tumor islands were separated by areas of hyalinized collagen. Multinucleated giant tumor cells were found in the lumen of a medium-size vein underlying the tumor. The differential diagnosis of angiomatoid malignant fibrous histiocytoma, a tumor with clinical and morphologic similarities, is discussed.

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We describe a patient in whose family 13 of 26 members have a palmo-plantar keratoderma. The histopathological findings in the proband, his brother and father were those of epidermolytic hyperkeratosis. As in other families reported, this disorder was found to be inherited as an autosomal-dominant trait. A review of the literature on the clinical, genetic and associated features of this genodermatosis is presented. We also review the cutaneous conditions that may exhibit the histopathological pattern of epidermolytic hyperkeratosis.

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