Clinicopathologic features of 28 cases of nail matrix nevi (NMNs) in Asians: Comparison between children and adults

Background: Clinical distinction between nail matrix nevus (NMN) and subungual melanoma (SUM) can be challenging. More precise delineation of the clinicodermoscopic characteristics specific for NMNs is needed. Objective: We sought to analyze the clinicopathologic features of childhood and adult NMNs and to propose clinicodermoscopic features that can aid in differentiating NMNs from SUM. Methods: We retrospectively reviewed clinical, dermoscopic, and histologic findings of patients (20 children and 8 adults) in whom NMN was diagnosed between 2012 and 2015. Results: Except for 2 cases of total melanonychia, the affected nails demonstrated longitudinal melanonychia sharply demarcated from the adjacent nail plate. Melanonychia was wider among children than among adults (P = .002). Nail dystrophy was more frequent in wider lesions (P = .028). Hutchinson's sign was observed in pediatric cases at the hyponychium and/or proximal nailfold cuticles. All hyponychial pigmentations demonstrated a longitudinal brush pigmentation pattern under dermoscopy. Limitations: This was a retrospective study of Asians in a single center. Conclusion: Our study is the largest case series to date of biopsy-confirmed NMNs. It highlighted important clinicodermoscopic differences between pediatric and adult NMNs. We propose that in pediatric cases of longitudinal melanonychia presenting as a sharply demarcated pigment band of even width, the presence of Hutchinson's sign with longitudinal brush pigmentation may favor a diagnosis of NMN over SUM.