ABSTRACT
B Hyperpigmentation and hypertrichosis are more prominent in Becker’s nevus
B Transient piloerection or elevation of a lesion induced by rubbing (pseudo-Darier sign)
Histopathology: Smooth Muscle Hamartoma: B Discrete, hyperplastic smooth muscle bundles within the
reticular dermis (Fig. 1B) B Smooth muscle bundles oriented in varying directions
(Fig. 1C) B Some smooth muscle bundles connect to hair follicles
Becker’s Nevus: B Hyperkeratosis, acanthosis, and hyperpigmentation of
the overlying epidermis (Fig. 2B) B The rete ridges have flat bases and rectangular shapes B Increased bundles of smooth muscle in the dermis
(Fig. 2C)
Features Congenital Smooth Muscle Hamartoma Becker’s Nevus
Clinical Present at birth Onset in childhood or adolescence
Trunk and proximal extremities
Upper half of trunk and shoulder
Histopathologic Epidermal changes and hyperpigmentation may be absent
Epidermal changes, hyperpigmentation, and hypertrichosis prominent
Increase in smooth muscle bundles prominent
Increase in smooth muscle bundles variable
Features Smooth Muscle Hamartoma Pilar Leiomyoma
Clinical Single large patch or plaque
Multiple, small, reddish-brown nodules
Histopathologic Discrete bundles of smooth muscle extending in different directions
Interlacing bundles of smooth muscle
Clinicopathologic Correlation: Congenital smooth muscle hamartoma and Becker’s nevus may be considered as a spectrum with varying amounts of smooth muscle hyperplasia, variable hyperpigmentation, and hypertrichosis.
