Pityriasis rubra pilaris: epidermal cell kinetics.

Epidermal proliferative kinetics were studied in a patient with pityriasis rubra pilaris. Elevated proliferative indices (flash labelling and mitotic indices) were apparent compared with normal epidermis and measurements of the birth rate indicate that the rate of epidermal cell production was similar to that found in psoriasis, and equalled 11.8 cells/1000 germinative cells/h; this suggests a cell cycle time of 60 h. Contemporaneous measurements of the rate of entry into DNA synthesis showed values similar to the rate of entry into mitosis; hence there is no G2 cell loss as appears to occur in the hyperproliferative psoriatic epidermis.