Congenital smooth muscle hamartoma*

Abstract

Dear Editor, Congenital smooth muscle hamartoma is defined as a rare asymptomatic benign skin defect detected in newborns and young children. Clinically it manifests as a hyperpigmented or skin-colored plaque where prominent vellus hairs may be observed.1,2 The condition is characterized by the proliferation of smooth muscle bundles in the dermis, which can reach the hypodermis where a connection to the hair follicle may occur.1,3 Due to its atypical manifestation, it may be confused with other cutaneous diseases, thus histological confirmation is necessary.1-5 A 56-day-old Caucasian girl from São José do Rio Preto – SP, born with 33 weeks due to a cesarean twin birth, presented with a brownish macula in the posterior region of the right thigh that had appeared 19 days after birth. Physical examination revealed a hyperchromic plaque with discreet palpation, regular contours and absence of hair. Rubbing the lesion produced a transient erythema suggesting a pseudo-Darier’s sign (Figure 1). Initially, the diagnostic hypotheses included: solitary mastocytoma, Becker’s nevus, pilar leiomyoma, and smooth muscle hamartoma. We performed an ultrasound of the soft parts of the lesion that revealed a discrete obliteration of skin and subcutaneous cellular tissue, and absence of changes in the musculature. No images suggesting cystic or solCongenital smooth muscle hamartoma*