Clinicopathological diversity and outcome of longitudinal melanonychia in children and adolescents: analysis of 35 cases identified by excision specimens.

ABSTRACT

AIMS: Longitudinal melanonychia in paediatric patients often represents a difficult diagnostic challenge, and studies emphasising its clinical and histopathological features are limited due to its low incidence in childhood. METHODS AND RESULTS: We retrospectively analysed 35 paediatric cases identified by excision specimens on their clinicopathological features, and performed fluorescence in-situ hybridisation on 13 available cases. Fingernails (77.1%) were more likely to be affected. Total melanonychia and Hutchinson's sign were observed in 10 (28.6%) and 14 (40.0%) cases, respectively. Nail dystrophy at diagnosis was present in five cases. After complete excision of the lesions, four patients relapsed during follow-up (mean = 38 months). Seventeen cases were diagnosed as lentigines and 18 as naevi, among which 11 cases were categorised as lentigines/naevi with atypical melanocytic hyperplasia. Mild-to-moderate nuclear atypia, confluency of melanocytes, focal pagetoid spread and peri-ungual skin involvement were found in 25.7% (9 of 35), 40.0% (14 of 35), 40.0% (14 of 35) and 40.0% (14 of 35) of cases, respectively. Thirteen cases tested by fluorescence in-situ hybridisation showed no copy number aberration at the probed loci. There was a statistically significant difference in the following features between patients aged less and more than 10 years (P < 0.05) cytomorphology, mild-to-moderate nuclear atypia, confluency of melanocytes, focal pagetoid spread and melanocyte count. CONCLUSIONS: Some concerning clinicopathological characteristics, which are signs indicative of melanoma in adults, are not uncommon in paediatric longitudinal melanonychia, especially in patients aged ≤ 10 years. Owing to the extremely low incidence of melanoma in paediatric longitudinal melanonychia, in most circumstances a more conservative clinical management strategy should be adopted.