Intraoperative Nail Matrix Assessment in Longitudinal Melanonychia

Longitudinal melanonychia (LM) may represent subungual melanoma (SUM), yet clinical differentiation from benign LM remains challenging. Intraoperative dermoscopy (IOD) improves diagnostic accuracy but requires specialized equipment and time. Intraoperative nail matrix examination (IONME), a direct visual inspection without magnification, may provide a simpler alternative. This study evaluated the diagnostic performance of IONME compared with histopathology and nail plate dermoscopy.

A retrospective analysis of 110 LM cases (16 SUM in situ, 94 benign LM, of which 88 were melanocytic) with documented IONME was performed. IONME patterns were classified into three morphological categories: (a) barely visible homogeneous pigmentation or none, (b) regular lines and/or homogeneous spot, and (c) irregular variegated lines. Each pattern was correlated with histopathology. Diagnostic accuracy, sensitivity, and specificity were calculated by comparing SUM in situ with benign melanocytic LM (mLM). Intra-observer agreement was assessed using Cohen's κ.

An irregular IONME pattern was observed in 87.5% (14/16) of SUM in situ versus 21.6% (19/91) of benign mLM (p < 0.001), yielding sensitivity of 0.88 and specificity of 0.78. In comparison, nail plate dermoscopy demonstrated lower accuracy (sensitivity, 0.81; specificity, 0.55). The barely visible pattern occurred exclusively in benign LM, while the regular pattern predominated in melanocytic activation and lentigo. Intra-observer agreement for pattern classification was excellent (κ = 0.84-0.88; p < 0.001). Agreement for the presence of an irregular pattern ranged from excellent to perfect (κ = 0.94-1.00; p < 0.001).

IONME is a simple, equipment-free intraoperative tool that improves clinicopathologic correlation, aids in distinguishing SUM in situ from benign LM, and supports patient follow-up. It can be easily incorporated into routine LM biopsy documentation.