Subungual exostosis.

Subungual exostosis (SE) is a relatively uncommon benign tumor of the bone occurring in the distal phalanx of a digit. Its similarities to other dermatologic disorders involving the nail bed often can lead to misdiagnosis, which may result in inadequate or extreme treatments. We present a case of a 20-year-old man with an exquisitely tender lesion on the distal phalanx of the left fourth toe. We also review the clinical presentation, pathogenesis, histologic and radiographic findings, diagnosis, and treatment of SE.