Dermoscopy provides useful information for the management of melanonychia striata.

The diagnosis of melanonychia striata is often difficult, and a biopsy of the nail matrix is required in doubtful cases. However, dermoscopic examination of the nail plate offers interesting information in order to better select the cases in which pathologic examination is indicated. In the case of brown longitudinal pigmentation with parallel regular lines, the diagnosis of nail apparatus melanocytic nevus could be made. On the other hand, the presence of a brown pigmentation overlaid by longitudinal lines irregular in their thickness, spacing, color, or parallelism is highly in favor of a melanoma. Gray homogeneous lines are observed in case of lentigo, lentiginoses, ethnic or drug-induced pigmentations, and in post-traumatic pigmentations. Blood spots are characterized by their round-shaped proximal edge and their filamentous distal edge and are highly suggestive of subungual hemorrhages. Dermoscopic examination of the free edge of the nail plate gives information on the lesion location; pigmentation of the dorsum of the nail plate is in favor of a proximal nail matrix lesion, whereas pigmentation the lower part of the nail edge is in favor of a lesion of the distal matrix.