Proposed classification of longitudinal melanonychia based on clinical and dermoscopic criteria

For longitudinal melanonychia, clinical and dermoscopic criteria for differentiating malignant melanoma in situ from benign nevus/lentigo/functional melanonychia have not been fully established.

To propose a clinical classification of longitudinal melanonychia that is useful in judging the need for follow-up.

A total of 137 patients with longitudinal melanonychia referred to our outpatient clinic in the most recent eight years were included. The mean and median lengths of follow-up for patients were 5.0 and 5.5 years, respectively. We classified the 137 lesions into three types by clinical and dermoscopic features of the nail and periungual skin, including Hutchinson sign, variation of color, and borders in the pigmentation band. We observed type I and II lesions with dermoscopy every six months and three months, respectively.

After follow-up, all 72 lesions classified as type I were thought to be benign nevus/lentigo/functional melanonychia. Five of the 52 lesions classified as type II showed enlargement during follow-up, and biopsy was performed. Of these five lesions, three were diagnosed as nevus/lentigo, and the other two were diagnosed as malignant melanoma in situ. All 13 lesions classified as type III were diagnosed as malignant melanoma in situ.

We can expect a type I lesion to be a benign nevus/lentigo/functional melanonychia and a type III lesion to be a malignant melanoma in situ; however, type II lesions fall in a gray zone. We believe this classification is useful in deciding treatment and follow-up.