Follicular occurrence of prurigo nodularis.

Thirty-eight biopsies of prurigo lesions (22 large, mature nodules and 16 smaller, intermediately developed nodules) were obtained from 17 patients with idiopathic prurigo nodularis Hyde who had not been bitten by insects, nor had other underlying diseases. Each biopsy was serially sectioned to reveal its histological structure. In 88% (14/16) of the smaller nodules and in 55% (12/22) of the large ones, a hair follicle was observed in the center of the prurigo lesion. The follicular epidermis and the adjacent surface epidermis showed various degrees of acanthosis and spongiosis. The dermal infiltrates extended from the superficial dermis into the middle dermis in a triangular fashion around the involved hair follicle. It is suggested that idiopathic prurigo nodularis most frequently occurs in connection with a hair follicle.