Ultrasound Measurements of the Median Nerve at the Distal Wrist Crease Correlate with Electrodiagnostic Studies
Nicholas Aloi, BS1, Landon Cluts, BS1 and John R Fowler, MD2, (1)University of Pittsburgh School of Medicine, Pittsburgh, PA, (2)UPMC, Pittsburgh, PA
Introduction: Carpal tunnel syndrome (CTS) is the most common nerve entrapment neuropathy that can be diagnosed with electrodiagnostic studies (EDS). Ultrasound (US) has emerged as a potentially easier and more comfortable alternative to EDSs. The purpose of this study is to evaluate whether measurements of the cross-sectional area of the median nerve via ultrasound correlates with the severity rating of CTS (i.e. normal, mild, moderate, or severe) based on EDSs.
Materials and Methods: This study was a retrospective review of patients ≥18 years who underwent US and EDSs of the median nerve for CTS between Oct 2014 and Dec 2020. Peak latency of the sensory nerve action potential (SNAP), distal motor latency of the compound muscle action potential (DML), and CMAP amplitudes were measured and the severity was graded based on AAEM guidelines. Cross-sectional area of the median nerve was measured via ultrasound. The Pearson Correlation coefficient was used to evaluate the relationship between US measurements of the distal wrist crease median nerve and EDS measurements. The F-test for linear trend was used to test for a linear relationship across the four EDS severity categories. ROC graphs were generated to find the optimal cut-off point for each level of EDS severity based on the Youden index.
Results: 273 wrists from 188 patients were included in this study. Patients with normal EDSs compared to those that had EDS evidence of CTS showed a mean median nerve CSA of 7.48 ± 2.00 mm2 versus 11.74 ± 3.76 mm2 (P-value < .0001). There was a significant association between wrist CSA and EDS severity (P < 0.0001) and it was shown that increasing CSA and increasing EDS severity are correlated (P < 0.0001). Pearson correlation coefficients demonstrated that US measurements are strongly correlated with increasing DML, SNAP, and decreasing CMAP amplitude (P<0.00001). The area under the curve, 0.867 (P < 0.001), demonstrated a significant ability for the distal wrist crease CSA to discriminate between normal EDS vs. abnormal EDS with an optimal cut-off point of ≥10 mm2, as well as the ability to discriminate between the varying levels of EDS severity.
Conclusions: The results of this study show that US measurements of the distal wrist crease CSA correlates strongly with EDS measurements, and that distal wrist crease CSA may discriminate between normal vs. abnormal EDS, as well as being able to discriminate between mild, moderate, and severe EDS ratings of active CTS.
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