Same inception, divergent fate: Evolving onychoscopic criteria for longitudinal melanonychia suggesting the onset of nail melanoma

Abstract

Longitudinal melanonychia (LM) is a brown–black longitudinal band extending from the proximal nail plate to the distal margin, which may be benign or indicative of melanoma. Digital onychoscopy follow-up is crucial for tracking alterations in LM over time, facilitating early malignancy identification by monitoring new pigmentation patterns or changes in existing ones. The research presented in this article by Moscarella et al.1 aimed to characterize the clinical and onychoscopic changes in a series of LM cases. There remains a necessity for guidelines to determine the optimal frequency and duration of onychoscopic follow-ups for patients with LM, as well as specific onychoscopic criteria for the early detection of nail unit melanoma (NUM). For this, one should master advanced onychoscopy to ascertain whether the nail pigmentation results from activation or proliferation and, in the case of the latter, determine whether it is benign or malignant.2 The primary objective of this retrospective cross-sectional study was to investigate the clinical and onychoscopic alterations in 62 adult cases with LM. The observation that no significant differences were detected between benign LM and melanomas regarding nail band colour, width or regularity during the initial clinical examination highlights the challenges in diagnosing NUM in its early stages. The authors highlighted three onychoscopic features statistically correlated with NUM, as they occurred during digital onychoscopy monitoring: emergence of granular pigmentation, increase in pigmentation intensity and rise in the number of colours. The main limitation of this study is the underrepresentation of skin of colour. The results of this study may most probably not be extended to darker phototypes, as they typically exhibit darker bands with brown–black backgrounds, where lines and granulation may be almost indistinguishable compared to lighter phototypes, where these are easily noticeable. The restricted inclusion of pigmented lesions, together with the small number of melanoma cases identified during follow-up, constitutes additional limitations. Another limitation is that about one-third of all NUM are amelanotic3 and do not present as LM. The results are notable and have substantial implications for clinical practice, given the absence of a defined methodology for clinical and onychoscopic follow-up in patients with LM. This also demonstrates the substantial need for improved training in digital onychoscopy follow-up, which could augment dermatologists' confidence in managing LM. One should remember that adult onychoscopic criteria cannot be applied to children. LM in childhood behaves completely differently, and the risk of melanoma in children is almost nil. A meta-analysis comparing atypical clinical and onychoscopic signs in adults and children with LM indicated that children exhibit more multicoloured bands and the Hutchinson sign.4 The lack of a definite age threshold for paediatric versus adult diagnostic criteria sometimes makes LM in teenagers and young adults difficult in decision-making. According to Lee et al.,5 a malignancy should be considered in patients exhibiting LM with high band colour intensity, variegation, nail plate splitting, Hutchinson sign and band change (Figure 1), and a removal of the whole pigmented matrix area should be conducted. These results, when combined with those from the study by Moscarella et al.,1 provide clinical and onychoscopic indicators of NUM in patients whose LM diagnosis is questionable. Artificial intelligence improves non-invasive imaging methods such as dermoscopy and optical coherence tomography for diagnosing and evaluating skin lesions. The integration of onychoscopic images into convolutional neural networks (CNN) could facilitate the automated analysis of pigmented nail lesions. This technology could improve the monitoring of longitudinal melanonychia by enabling earlier diagnosis in cases of subtle changes that might escape the dermatologist's attention. None to declare. None to declare. The patient in this manuscript has given written informed consent to publication of their case details. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.