Congenital smooth muscle hamartoma. Prevalence, clinical findings, and follow-up in 15 patients.

Cogenital smooth muscle hamartoma is a congenital skin lesion characterized by proliferation of bundles of smooth muscle within the reticular dermis. We report on a group of 15 children with this lesion, confirmed by skin biopsy specimen, its prevalence, the occurrence of associated anomalies, and long- term follow-up. To our knowledge, this is the largest group of patients with this lesion described in the literature. The estimated prevalence is about 1:2600 live births with slight male predominance. The lesion is most frequent in the lumbosacral area (67% [10/15]) and a positive pseudo-Darier's sign is present in 80% (12/15) of patients. During the follow-up period of up to 7 years, the lesions enlarged slightly but became less prominent. No malignant transformation was observed.