Morphologic investigations on the rebound phenomenon after corticosteroid-induced atrophy in human skin.

Cutaneous atrophy was induced on the forearms of 4 volunteers by continuous occlusive application of clobetasol-17-propionate for 6 weeks, after which time the steroid was discontinued. Epidermal and dermal changes during the subsequent rebound "flare" were monitored for 2 weeks by light and transmission electron microscopy. An exuberant hyperplasia characterized the epidermal response. Within 2 days poststeroid, most basal cells displayed fine structural features typical of highly proliferating cells. "Dark"-staining keratinocytes appeared in large numbers 4 days poststeroid, preceding a 4-fold maximal increase of viable epidermal thickness which occurred at 7 days. The stratum corneum, initially very thin, increased markedly in thickness and displayed the typical basket-weave appearance. By 14 days, Langerhans cells, which were absent immediately poststeroid, were again present. At this time, the epidermis returned to a nearly normal state. Dermal restitution was similarly rapid. Initially, fibroblasts appeared very active as evidenced by widely dilated endoplasmic reticulum filled with flocculent material. Ground substance increased continuously, reaching normal levels by 14 days. An increase in postcapillary venules was noted during the rebound flare. Swift epidermal and dermal changes are evidence that topical corticosteroids are rapidly cleared from the skin. The vigorous epidermal hyperplasia reflects repair of the atrophic, suppressed epidermis as well as a response to desiccation consequent to the loss of the stratum corneum.