Pigmented Onychomatricoma: A Rare Pigmented Nail Unit Tumor Presenting as Longitudinal Melanonychia That Has Potential for Misdiagnosis as Melanoma.

Pigmented onychomatricoma is a rare nail unit tumor that can clinically mimic nail unit melanoma. We report the case of a 63-year-old male with new-onset longitudinal melanonychia involving his right second toe. An excisional biopsy was performed and demonstrated pigmented onychomatricoma. We present this case to alert clinicians of this rare nail unit tumor and the importance of clinicopathologic correlation to avoid misdiagnosis.