Cutaneous pilar leiomyoma: clinicopathologic analysis of 53 lesions in 45 patients.

As cutaneous pilar leiomyomas have received little attention in the recent literature, 53 lesions from 45 patients were studied to analyze their clinicopathologic features. There was an equal distribution between both sexes; most patients were adults with a wide age distribution. Both multiple (29 lesions from 21 patients) and solitary tumors (18 patients) were included. Lesions on the extremity (29 tumors) were common in both groups, whereas truncal tumors (11) were confined largely to patients with multiple lesions. In six patients the number of lesions was not specified. The tumors were painful in 17 patients. Three patients had a positive family history of similar lesions. Histologic study revealed ill-defined bundles of well-differentiated smooth muscle cells in the reticular dermis in all cases, although nine lesions had a more nodular pattern. Overlying epidermal hyperplasia was noted in 29 cases (54.7%). Immunohistochemically there appeared to be an increased number of nerve fibers within and surrounding the tumors. Mitotic activity was observed in 15 lesions (28.3%), 13 of which had <1 mitosis per 10 high power fields (HPF); the remaining two lesions had 1-2 mitoses per 10 HPF. Follow-up was available in 10 of these mitotically active tumors and ranged from 9 months to 7 years. There was no recurrence in any of them. We have concluded tentatively that leiomyomas of arrector pili origin may exhibit a low mitotic activity of <1 per 10 HPF and that this does not adversely affect the prognosis for these patients.