[Pinkus' trichodiscoma (author's transl)].
The trichodiscoma first described by Pinkus (1966) is a small cutaneous tumor of the human retropilar hair disk; these lesions generally multiple and probably more common than previously appreciated occur in adult patients most often associated with perifollicular fibromas and acrochordons. We observed 2 female patients (39 and 47-year-old) with multiple trichodiscomas; a linear group of 7 tumors on the scalp in the first and multiple lesions disseminated on the chest in the second. Histologically and--in one case--electronmicroscopically the most striking features are: the paucity of the Merkel's cells in the overlying basal layer of the epidermis, the hyperplasia of the capillary blood vessels and of their endothelial cells, the presence of thick myelinated nerve fibers in the depth of the lesion but not in the vicinity of the epidermis, the proliferation of a loose dermal connective tissue, the occurrence of sparse hair follicles connected to the trichodiscoma but frequently located on its margin. One can conclude that trichodiscoma mainly consists of a hyperplasia of the dermal components of the hair disk; Merkel's cells though belonging to the normal hair disk are not involved in the histogenesis of the tumour. In his comprehensive paper (1974), Pinkus predicted that the description of the trichodisoma will lead to the identification of patients having only one or a few lesions: our first case may be considered as a circumscribed paucilesional clinical form.