Photofibrosis: a further histopathological change induced by PUVA therapy via the mast cell in guttate psoriasis. Preliminary report.

Twenty-five psoriatic patients were studied histologically before and after PUVA therapy in order to delineate the relationship between dermal mast cells, psoriasis healing process and collagen changes. A number of mast cells were found in the psoriatic changes. A number of mast cells were found in the psoriatic lesion both before PUVA and also after PUVA therapy in 22 of the 25 patients. Fibrosis of the papillary dermis and upper reticular dermis was found in 3 cases. Increased collagen deposition and increased numbers of fibroblasts were accompanied by verticalization of ectatic and elongated blood vessels, with an overall pattern of relatively recent scarring. Mast cells were no longer detectable in the fibrosis area. We cannot exclude the possibility that PUVA therapy exerts a further stimulus on mast cell histamine and heparin degranulation in this type of psoriasis, thus leading to dermal fibrosis and blood vessel neogenesis.