Nail Unit Squamous Cell Carcinoma with Onycholemmal Features: Case Report and Review of the Literature.

INTRODUCTION: Onycholemmal carcinoma (OC) is a rare subtype of squamous cell carcinoma (SCC) that originates from the epithelium of the nail bed. It is characterized by distinct histopathologic features including small clusters of atypical squamous epithelium devoid of a granular layer, with abrupt onycholemmal keratinization.

CASE PRESENTATION: We present a case of a 75-year-old male with right thumbnail onycholysis, yellow-green nail plate discoloration, as well as bleeding and purulence of the lateral nail fold. Histopathologic evaluation revealed high-grade squamous dysplasia, small clusters of severely atypical epithelial cells, and a pattern of abrupt keratinization consistent with the diagnosis of SCC carcinoma with onycholemmal features. GMS and PAS staining indicated concomitant onychomycosis. Pathologic analysis also disclosed residual SCC and concomitant amyloidosis, possibly light chain related and hence reflective of his underlying multi-organ lymphoplasmacytic lymphoma. The patient subsequently underwent Mohs micrographic surgery.

CONCLUSION: Clinical presentation of nail unit SCC with onycholemmal features is highly variable, making differentiating between similarly presenting benign and malignant nail disorders particularly challenging. This case report demonstrates clinical and histopathological features of nail unit SCC with onycholemmal features to improve diagnosis and management.