Unusual Case of Nail Unit Melanoma.

We present a case of a nail unit melanoma with chondroid differentiation that was initially misdiagnosed as a benign chondroid neoplasm. A 67-year-old Caucasian woman presented to an outside dermatologist with a tender subungual nodule on the right index finger with overlying nail plate changes that had been present and enlarging for 1 year. Initial histopathological evaluation rendered a diagnosis of benign chondroid neoplasm. On arrival to our institution, magnetic resonance imaging was performed, and the lesion appeared consistent with a glomus tumor. Plastic surgery performed a surgical resection with intraoperative frozen sections revealing a hypocellular cartilaginous mass, but pathology was unable to comment on the presence of malignant cells. On permanent sectioning of the excised lesion, a lentiginous proliferation of melanocytes overlying a dermal aggregate of atypical cells with conspicuous mitoses embedded in a chondroid matrix was seen. A panel of immunohistochemical stains was performed, including SOX-10, HMB-45, S-100, MITF and MART1 was performed with SOX-10, HMB-45, and S-100 staining the junctional melanocytes and dermal cells, rendering a diagnosis of primary chondroid melanoma.