Abstract

Onycholemmal carcinoma (OC) is a rare squamous cell carcinoma subtype of the nail bed epithelium with only 16 cases documented in the literature. OC typically presents as slow-growing onychodystrophy of a single fingernail or toenail of middle-aged to older adults, with the average age of diagnosis being 67 years old. OC is characterized histologically by atypical squamous epithelial cells organized in variably sized lobules with abrupt keratinization and is analogous to trichilemmal differentiation at this site. We present a case of a 28-year-old female with a 1-year history of a painful, erythematous nodule of the right index fingernail. The patient underwent an excisional biopsy, and on initial histologic consultation, findings were consistent with well-differentiated squamous cell carcinoma. A second histologic consultation of the lesion showed atypical squamous proliferation with dyskeratosis and trichilemmal differentiation. A third histologic consultation showed endophytic squamous proliferation with prominent dyskeratotic keratinocytes. The patient monitored the scar for 10 months until a new tender, erythematous growth recurred distal to the original site. A second biopsy was performed, and histological findings were consistent with onycholemmal carcinoma. MRI findings showed focal erosion of the 1st distal phalanx of the right hand with features suggesting pathologic fracture. OC can be treated with Mohs micrographic surgery or radiation in cases without bony involvement. However, amputation is indicated in cases of OC with bony involvement. The case report describes the first case of onycholemmal carcinoma in a young adult and demonstrates the importance of early detection of onycholemmal carcinoma to avoid amputation.