Looking Beyond the Hutchinson Sign: A Retrospective Study of Clinical Factors Indicating the Presence and Invasiveness of Nail Unit Melanoma in Patients With Longitudinal Melanonychia

BACKGROUND The data underlying this article are available in the article. Longitudinal melanonychia (LM) presents a challenge because nail unit melanoma (NUM) must be considered as a differential diagnosis. Because nail matrix biopsy may result in nail dystrophy, it is important to distinguish NUM from LM. OBJECTIVE To provide evidence of previously reported clinical factors indicative of NUM in patients with LM. METHODS This was a retrospective study of patients who presented with LM and had biopsy-confirmed NUM from 2005 to 2021. Benign LM was either confirmed by biopsy or considered benign if followed without the need for biopsy. Clinical factors associated with LM and NUM were compared by multivariate regression. RESULTS A total of 177 patients (97 LM and 80 NUM) were included. Multivariate regression showed that high band color intensity ( p = .0031), variegation ( p = .0005), nail plate splitting ( p = .0017), Hutchinson sign ( p = .0027), and band change ( p = .001) correlated with malignancy. Nail plate splitting was associated with Breslow thickness. CONCLUSION Malignancy should be suspected and biopsy performed in patients with LM and high band color intensity, variegation, nail plate splitting, Hutchinson sign, and band change.