Melanoma and squamous cell carcinoma on different nails of the same hand.

Nail dyschromia, including melanonychia and erythronychia, encompasses a wide range of possible diagnoses. While the majority of these lesions are benign, malignancies of the nail unit represent a sinister, and potentially life-threatening, cause of nail dyschromia. Unfamiliarity with tumors of the nail apparatus can lead to a delay in diagnosis. A case is presented of a patient with two separate and concurrent malignant neoplasms of the nail unit, on different nails on the same hand, each featuring an unusual clinical presentation: amelanotic melanoma presenting as longitudinal erythronychia and squamous cell carcinoma in situ presenting as longitudinal melanonychia. This presentation underscores the need for a low threshold for biopsy in the presence of nail dyschromia of uncertain etiology.