Congenital smooth muscle hamartoma on the scalp

Case Report An 8-day-old male infant was referred to our neonatal unitfor prematurity. It was observed that his scalp color wasdarker than the rest of his skin color when the scalp hair waspartially shaved for intravenous access. Dermatologic exam-ination revealed a slightly elevated, hyperpigmented plaqueconfined to the whole scalp. The margin of the lesion did notextend to the face and neck. His hair was abundant and dark(Fig. 1). There were no areas of alopecia and no overlyingfolds of skin. There were no dysmorphic features, such asMichelin tire baby. Pseudo-Darier’s sign was negative.A punch biopsy specimen was obtained from the lesionwith a diagnosis of congenital melanocytic nevus or congeni-tal blue nevus. The result of histopathologic examinationshowed increased smooth muscle bundles in the reticular der-mis running in various directions under a normal epidermis(Fig. 2a); immunohistochemical stain revealed desmin-positive (Fig. 2b) and S100-negative proliferation. Based onthese clinical and histopathologic findings, a diagnosis ofcongenital smooth muscle hamartoma was made. No changesin this lesion were observed during a 9-month follow-up period. Discussion Congenital smooth muscle hamartoma (CSMH) is a rarecutaneous dysembryoplasia characterized by a disorganizedproliferation of normal muscle fibers of arrector pili. Thedisease usually presents as a localized, skin-colored ormildly hyperpigmented, irregularly shaped patch or plaquewith prominent vellus hairs located on the lumbosacral area.