34216 Subungal squamous cell carcinoma presenting as longitudinal melanonychia

Abstract

An 85-year-old African American woman with erosive lichen planus, diabetes, and rheumatoid arthritis presented for evaluation of linear melanonychia of the right first fingernail. The lesion had been present for multiple years, slowly increasing in size, darkening, and becoming painful. Upon evaluation, the patient had a 4 x 2 mm pigmented macular lesion at the proximal nail fold with a 3-mm-wide pigmented streak extending to the end of the nail plate. No nail deformity, bleeding, or drainage was noted. Excisional biopsy of the nail matrix with 1mm margins was performed, yielding a 5 x 3 mm defect at the proximal nail fold. Histopathology revealed high-grade squamous intraepithelial lesions involving the epidermis and nail bed. Stain for Melan-A was positive in dendritic melanocytes and less than 1% of epithelial cells. Stain for p16 showed strong confluent staining with more than 90% of dysplastic epithelium. Positive p16 staining is consistent with HPV-associated squamous cell carcinoma (SCC). The diagnosis of subungual SCC was made and the lesion was further excised with Mohs micrographic surgery approximately 2 months later. A total of 2 stages and 4 tissue sections were required to obtain clear margins. The postsurgical defect was 23 x 21 mm and repaired using a rotation flap. This case of a rare malignant subungual tumor, SCC of the nail bed, is especially unique due to its presentation. The presence of a darkly pigmented streak is more typical of subungual melanoma. Awareness of various presentations of SCC of the nail bed, often called the “great mimicker,” is important as it is frequently misdiagnosed.