To investigate dermoscopic manifestations and features of melanonychia.

A retrospective analysis was carried out on dermoscopic images of 4 common types of melanonychia collected in Department of Dermatology, Xijing Hospital, the Fourth Military Medical University from January 2016 to July 2020.

A total of 266 cases of melanonychia were collected, including 64 (24.1%) of subungual melanoma, 52 (19.5%) of nail matrix nevi, 89 (33.5%) of subungual hemorrhage, and 61 (22.9%) of onychomycosis. Subungual melanoma and nail matrix nevi mostly occurred in the fingernails. To be specific, subungual melanoma most frequently occurred in the thumbnails (62.8%) , while nail matrix nevi mostly involved the 2^nd - 5^th fingernails (73.9%) . Subungual hemorrhage and onychomycosis mostly occurred in the toenails, and there were 51 (57.3%) cases of subungual hemorrhage of the toenails and 46 (75.4%) cases of onychomycosis of the toenails. Subungual melanoma mostly occurred in patients aged over 40 years (49 cases, 76.8%) , while the other 3 types of melanonychia mostly affected patients aged under 40 years. Dermoscopic manifestations of subungual melanoma mainly included regular longitudinal bands (35 cases, 54.7%) or irregular bands (25 cases, 39.0%) whose width was greater than 3 mm in 87.5% cases, Hutchinson sign (36 cases, 56.3%) , and ruptures (15 cases, 23.4%) which mainly were black-brown in color; dermoscopic manifestations of nail matrix nevi mainly were a single regular pigmented band (52 cases, 100%) whose width was less than 3 mm in 36 (69.2%) cases, and Hutchinson sign (26 cases, 50%) , while no ruptures were observed in nail matrix nevus lesions; subungual hemorrhage dermoscopically manifested as diffuse macules (74 cases, 83.1%) , and globular dark red or black hemorrhagic structures were observed in 85 (95.5%) cases; fungal melanonychia was dermoscopically characterized by irregular dark brown longitudinal bands (54 cases, 88.5%) .

Subungual melanoma was dermoscopically characterized by regular longitudinal bands with a width of greater than 3 mm, nail matrix nevi by regular longitudinal bands, subungual hemorrhage by diffuse macules, and onychomycosis by irregular longitudinal bands. Dermatoscopy can be used to identify melanonychia lesions and provide a basis for auxiliary diagnosis of subungual melanoma.

Nail diseases; Nevi and melanomas; Onychomycosis; Dermoscopy; Subungual hematoma; Longitudinal melanonychia