[Smooth muscle hamartoma: anatomoclinical characteristics and nosological limits].

Smooth muscle hamartoma is an uncommon cutaneous dysembryoplasia usually diagnosed in infancy. Among the 61 cases published since 1923, 56 were congenital and 3 appeared in young adults. We report a case in which the lesions started at the age of 15 years as a papular plaque in the right mammary region of a young woman. A review of the literature showed that the usual clinical presentation is a frequently pigmented plaque made of often follicular papules and measuring 1 to 10 centimeters on average. Excessive hairiness is the most frequent sign, being observed in more than two-thirds of the cases, and Darier's pseudo-sign is present in about 53 p. 100 of the patients. The disease is electively located on the lumbar region, the back and the root of the limbs. In 3 cases the lesions were generalized and the patients looked like fatty "Michelin-Tire Babies". The course of the disease is always favourable, and associated pathologies remain exceptional: urticaria pigmentosa and psychomotor retardation have been reported in two cases of the generalized form. Histology is characterized by the presence of numerous smooth muscle fibres disseminated in the dermis and diversely oriented, sometimes in contact with hair follicles which retain their normal morphology. The differential clinical diagnosis is with naevocytic naevus, café-au-lait spots, mastocytosis and connective tissue hamartoma. Belatedly revealed forms of the disease must be distinguished from Becker's hamartoma, but it must be known that in certain cases the classification is so difficult that some authors have suggested that smooth muscle hamartoma and Becker's hamartoma are only two poles of a single spectrum of dysembryoplastic lesions involving to varying degrees the epidermic and hair structures. Finally, the distinction between the localized forms of late onset smooth muscle hamartoma and multiple leiomyomas "en plaques" remains difficult both anatomico-clinically and nosologically.