Metastases to the nail unit and distal phalanx: a systematic review

Metastases to the nail unit/distal phalanx (NU/DP), although rare, carry a poor prognosis and are frequently misdiagnosed due to variable clinical presentation. Metastases to the NU/DP may be the initial presenting sign of a new or recurrent malignancy. Since the most recent systematic review of case reports (133 patients total) was conducted in 2001, we conducted a systematic review from 1900 to 2021 (244 patients total) to assess any changes in trends in demographics, clinical presentation, and morphology and to report on more updated differential diagnoses. We also examined cases for age, sex, race, ethnicity, Fitzpatrick skin type, laterality, distribution, and diagnostic methods. The PubMed database (1900-2021) was used to detect case-level data per Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We found that the most common primary tumors were lung, kidney, and esophagus. A NU/DP metastasis was the presenting sign of malignancy in 31.00% of patients without a former cancer diagnosis. Male to female ratio was 2:1, with average age at diagnosis 58 years. Metastases most often affected a single digit (79.91%), particularly the thumb, followed by the fourth digit. This systematic review corroborates that metastases to the NU/DP may be the initial presenting sign of a new or recurrent malignancy and provides updated diagnostic guidelines. NU/DP metastasis should be considered in both healthy patients and patients with a former malignancy diagnosis presenting with nail changes involving a single digit. Prompt diagnosis and treatment may improve prognosis.