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What Causes Neurofibromas?

Neurofibromas are proliferations of peripheral nerves and the surrounding collagenous matrix. They occur sporadically and as part of the neurofibromatosis type I syndrome (NF1). Results of earlier studies suggest that trauma may play a role in their etiology, but this has not been proven. In this study from Finland, investigators examined skin biopsies taken from clinically uninvolved skin of 10 patients with NF1 and from 6 patients with no evidence of the disease.

Researchers detected a small, clinically unapparent neurofibroma in the deep dermis surrounding a hair follicle in the biopsy of 1 patient with NF1 and a smaller but histologically similar collection of cells at the same location in a biopsy taken from another NF1 patient. Specimens from several of the remaining patients with NF1 demonstrated an increased presence of perifollicular nerve cells (as evidenced by S100 protein staining). They identified no such increases in the control tissue.

Comment: This study provides several interesting, albeit preliminary, insights into the pathogenesis of neurofibromas. The authors suggest that the presence of increased numbers of nerves and collagenous matrix components in the apparently normal skin of patients with NF1 supports the notion that neurofibromas are reactive proliferations and not true neoplasms. Further, they argue, the presence of these components around hair follicles may suggest that trauma caused by the interactions of the arrector pili muscles with the follicular epithelium and surrounding dermis may contribute to neurofibroma development. It should be noted, however, that these observations and conclusions are based on a study of just 10 NF1 patients, only 2 of whom had significant histologic findings. (Four additional patients showed subtle increases in neural elements). In addition, the neurofibromatous proliferations in the images that accompany the article appear to be near the base of the hair follicle, whereas arrector pili muscles are anatomically separate from this area. In summary, this is a fascinating study that certainly warrants further confirmatory research.

— BS Smoller

Published in Journal Watch Dermatology November 6, 2000

Citation(s):

Karvonen SL et al. Occult neurofibroma and increased S100 protein in the skin of patients with neurofibromatosis type 1. Arch Dermatol 2000 Oct 136 1207 -1209.

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