Cutaneous mast cell depletion results from topical corticosteroid usage.

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Abstract
The effect of long-term topical application of corticosteroids on human cutaneous mast cells was examined. Two potent corticosteroids, clobetasol-17-propionate and fluocinonide, produced a greater than 85% decrease in histamine content over a 6-wk treatment period, whereas betamethasone valerate, a less potent corticosteroid, produced a 66% decrease. Electron microscopic examination of the biopsies taken from sites after 6 wk of treatment indicate that the reduced levels of histamine were caused by the depletion of mast cells, as evidenced by: the inability to identify any cells representative of mast cells by detailed electron microscopy of the biopsies; and the marked acellularity around the vasculature where mast cells are certain to be detected. Histamine levels did not begin to decline until after 3 wk of corticosteroid treatment, indicating that corticosteroids are not immediately harmful to mast cells. Electron microscopic examination of biopsies taken at the beginning of treatment and 1 wk later showed normal-appearing mast cells, whereas at 3 wk, a small population of mast cells was detected with features usually associated with degenerating or dying cells. These observations suggest that protracted application of corticosteroids to skin is toxic to mast cells. After discontinuation of treatment, the drug-related atrophy associated with chronic application of potent corticosteroids to skin is rapidly reversed, and skin structure returns to near normal by 14 days. Over this time period, however, histamine levels did not increase and mature mast cells could not be observed by electron microscopy. At 14 days post-steroid treatment, the first signs of cells containing sparse amounts of granules having the characteristics of mast cell granules were seen. We interpret this to represent new mast cells beginning to mature in the skin. By 3 mo, histamine levels returned to normal, demonstrating the reversibility of the steroid-induced mast cell depletion. The studies presented here establish the deleterious effects of long-term topical corticosteroid treatment on cutaneous mast cells, and begin to establish a system in which the development of mast cells in tissue can be investigated.