A 36-year-old white woman presented with a 5-month history of an irritating lesion on her left shoulder. A crusted scab had arisen and fallen off, leaving her with a 1.5-cm, smooth, tender, intradermal nodule with no obvious surface abnormality (Figure 1).
The differential diagnosis included a keloid scar, adnexal tumor, and amelanotic melanoma. A biopsy specimen from the center of the lesion was obtained for histologic (Figure 2) and immunohistochemical staining with α-smooth muscle actin (Figure 3). The nodule remained exquisitely tender, and a complete excision was performed.
Laube S, Boyde AM, Motley RJ. Nodule on the Shoulder of a Young Woman. Arch Dermatol. 2002;138(11):1509. doi:10.1001/archderm.138.11.1509