Decreased urinary histamine metabolite after successful PUVA treatment of urticaria pigmentosa.

The effect of PUVA therapy on pruritus, the skin mast cell population and histamine metabolism has been studied in 3 patients with urticaria pigmentosa and manifestations of systemic mastocytosis. Relief of itch was found concomitant with a significant decrease of the major histamine metabolite 1-methyl-4-imidazoleacetic acid in the urine. The decrease occurred during the first 2 mo after starting PUVA therapy and was sustained during an observation period of 3 mo after discontinuation of the treatment. At this time a reduction of the number of mast cells was found in skin biopsy specimens. No evidence of acute histamine release in association with PUVA treatment was obtained. These results suggest that this effective new treatment for urticaria pigmentosa reduces the histamine turnover in the skin by inhibiting mast cell proliferation.