A Novel Ultrasonographic Anthropometric-Independent Measurement of Median Nerve Swelling in Carpal Tunnel Syndrome: The “Nerve/Tendon Ratio” (NTR)

• Published in: Diagnostics
• Main Authors: Paolo Falsetti, Edoardo Conticini, Caterina Baldi, Emilio D’Ignazio, Suhel Gabriele Al Khayyat, Marco Bardelli, Stefano Gentileschi, Roberto D’Alessandro, Miriana D’Alessandro, Caterina Acciai, Federica Ginanneschi, Luca Cantarini, Bruno Frediani
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: carpal tunnel syndrome; median nerve; ultrasound; electrodiagnostics; neuropathy; Medicine (General); R5-920; DML
• Online Access: https://doi.org/10.3390/diagnostics12112621; https://doaj.org/article/bda03cdb4cb846f6877c5774d6e4a662

Background: There is little consensus on ultrasound (US) normative values of cross-sectional area of median nerve (MN-CSA) in carpal tunnel syndrome (CTS) because of its dependency on anthropometric parameters. We aim to propose a novel anthropometric-independent US parameter: MN-CSA/flexor radialis carpi CSA (FCR-CSA) ratio (“Nerve Tendon Ratio”, NTR), in the diagnosis of clinically and electrodiagnostic (EDS)-defined CTS. Methods: 74 wrists of 49 patients with clinically defined CTS underwent EDS (scored by the 1–5 Padua Scale of electrophysiological severity, PS) and US of carpal tunnel with measurement of MN-CSA (at the carpal tunnel inlet), FCR-CSA (over scaphoid tubercle) and its ratio (NTR, expressed as a percentage). US normality values and intra-operator agreement were assessed in 33 healthy volunteers. Results: In controls, the mean MN-CSA was 5.81 mm 2 , NTR 64.2%. In 74 clinical CTS, the mean MN-CSA was 12.1 mm 2 , NTR 117%. In severe CTS (PS > 3), the mean MN-CSA was 15.9 mm 2 , NTR 148%. In CTS, both MN-CSA and NTR correlated with sensitive conduction velocity (SCV) ( p < 0.001), distal motor latency (DML) ( p < 0.001) and PS ( p < 0.001), with a slight superiority of NTR vs. MN-CSA when controlled for height, wrist circumference and weight. In CTS filtered for anthropometric extremes, only NTR maintained a correlation with SCV ( p = 0.023), DML ( p = 0.016) and PS ( p = 0.009). Diagnostic cut-offs were obtained with a binomial regression analysis. In those patients with a clinical diagnosis of CTS, the cut-off of MN-CSA (AUROC: 0.983) was 8 mm 2 (9 mm 2 with highest positive predictive value, PPV), while for NTR (AUROC: 0.987), the cut-off was 83% (100% with highest PPV). In patients with EDS findings of severe CTS (PS > 3), the MN-CSA (AUROC: 0.876) cut-off was 12.3 mm 2 (15.3 mm 2 with highest PPV), while for NTR (AUROC: 0.858) it was 116.2% (146.0% with highest PPV). Conclusions: NTR can be simply and quickly calculated, and it can be used in anthropometric extremes.