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S2C15P9-1: Pityriasis rubra pilaris might be better characterized as a clinical than as a histologic entity. For one of the two possible variants, this psoriasiform pattern perhaps is the most characteristic. The rete ridges are elongated; they vary more in width than in length. Some of the dermal papillae are widened and contain ectatic vessels. There is compact hyperkeratosis with focal parakeratosis. Degenerating inflammatory cells are present in the parakeratotic caps. The granular layer is irregularly hyperplastic. Peri-vascular infiltrates are mild in the upper portion of the dermis. The papillary dermis is widened and fibrotic. At the histologic level, this is a psoriasoform pattern with hyperkeratosis and focal parakeratosis.

S2C15P9-2: The hyperplastic epidermis of this example of pityriasis rubra pilaris shows well defined superficial and basal units. The two units are about equal in vertical dimensions. The keratin layer shows compact hyperkeratosis with deposits of melanin pigment. There are a few, widely scattered dendritic histiocytes in epidermis. The basal unit shows mild spongiosis. The papillary dermis is not significantly altered.

S2C15P9-3:This is another example of pityriasis rubra pilaris with compact hyperkeratosis, a prominent granular layer, and well defined basal and superficial units of the epidermis. The papillary dermis is not significantly altered. To the left, some of what appears to be parakeratosis may be nothing more than melanin pigment that has condensed as the dying keratinocytes have contracted to form keratinized lamellae .

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