(BMJ)—A man in his 20s had had an asymptomatic light tan patch on the L side of his chin since childhood. During puberty, he noticed that the hair was thicker in this area and required more-frequent trimming. Exam: well-circumscribed hyperpigmented patch with hypertrichosis in L submandibular region and L side of the neck, overlapping with beard area. No facial asymmetry. What’s the dx?
Postinflammatory hyperpigmentation
Congenital melanocytic nevus
Acanthosis nigricans
Smooth muscle hamartoma
Becker nevus
You are correct. The patient was diagnosed with Becker nevus, a cutaneous hamartoma characterized by localized, unilateral patchy brown hyperpigmentation with a well-demarcated geographical border. Occasionally, as in this patient, hypertrichosis is also present. Becker nevus is an androgen-dependent lesion that occurs mostly in men, although boys can also be affected. Although it typically develops on the upper trunk, it occasionally can be found elsewhere. Dx is based on clinical findings.

BMJ 2022;378:e072232