Dermoscopic features of nail unit melanoma: a scoping review

Nail unit melanoma (NUM) is a diagnostically challenging cutaneous malignancy that often presents with subtle or inconspicuous clinical features, contributing to delayed recognition and poorer outcomes. Dermoscopy has emerged as a valuable tool for improving early detection, yet the existing literature is fragmented and variably reported. This scoping review synthesized 26 studies encompassing 416 patients to characterize demographic patterns and dermoscopic features of NUM. Across included studies, most affected adults are in the fifth to sixth decades of life, with lesion duration at diagnosis ranging from < 1 year to > 10 years. Fingernails were more frequently involved than toenails, with the thumb and hallux predominating. A slight female and right-sided predominance was observed. The most consistently reported dermoscopic features were heterochromia, irregular band spacing and irregular bandwidth. Blurred borders were also frequently described, whereas the Hutchinson sign was observed in fewer than half of patients, underscoring its limited sensitivity. Invasive NUM was more frequently associated with destructive changes such as nail plate dystrophy and ulceration, whereas NUM in situ typically demonstrated subtler pigmentary abnormalities. Secondary features, including dots and globules, the triangle sign, vascular changes, blue-white veil, hyperkeratosis, the reverse triangle sign and superficial scale, were less consistently reported. These findings reinforce pigmentary irregularities as the most reliable dermoscopic indicators of NUM and highlight destructive features as markers of invasive disease. However, variability in reporting and limited stratification by disease stage underscores the need for standardized dermoscopic documentation and prospective, multicentre studies. Improved recognition of these features may support more timely biopsy decisions, reduce diagnostic delay and ultimately improve patient outcomes.