Digital dermoscopy follow-up for acquired longitudinal melanonychia

The differential diagnosis of early nail unit melanoma can be challenging.

This retrospective cross-sectional study aimed to characterize the clinical and dermoscopic changes in a series of cases of longitudinal melanonychia that underwent clinical and dermoscopic sequential digital monitoring.

All patients were adults presenting with a single acquired pigmented nail band and were monitored over time. Histologic diagnosis served as the gold standard for cases where excision was performed. For non-excised cases, inclusion in the study required a minimum of 1 year of documented clinical and dermoscopic stability. Clinical and dermoscopic features were assessed at baseline and during the final follow-up visit.

After a median follow-up of 17 months, 27 out of 62 lesions were excised. Among these, six cases (9.7%) were diagnosed as in situ melanomas, nine (14.5%) as nevi and 12 (19.4%) as lentigo or melanocytic hyperplasia. At baseline clinical evaluation, most of the bands, both benign and malignant, occupied less than one-third of the nail plate (62.5% and 50%, respectively). Comparing dermoscopic features between baseline and follow-up, granular pigmentation emerged in 33.3% of malignant nail bands but only in 3.6% of benign bands (p = 0.04). An increase in the number of colours was observed in 50% of in situ melanomas, compared with 8.9% of benign lesions (p = 0.02). Additionally, 83.3% of melanomas showed an increased intensity of pigmentation, a feature seen in only 14.3% of benign bands (p = 0.001). Limitations include the relatively small number of melanoma cases (n = 6), all cases were from pigment lesion clinics in Europe and involved only Caucasian patients. Lastly, only pigmented lesions were included, so no conclusions can be drawn regarding amelanotic subungual melanoma.

In conclusion, digital dermoscopy follow-up of longitudinal melanonychia is a valuable management strategy in uncertain cases. The emergence of new colours, granular pigmentation or increased intensity of pigmentation during follow-up should prompt a biopsy to rule out malignancy.