Neuromuscular ultrasound (NMUS) O-NU001. Feasibility of shear wave elastography and high definition color in evaluation of carpal tunnel syndrome

Abstract

Introduction . Diagnosis of carpal tunnel syndrome (CTS) is based on clinical findings and electrodiagnostic tests (EDT). However, EDT has high false negative rates, and the results often do not reflect the severity of symptoms. The aim of this study is to investigate the value of shear wave elastography (SWE) and high definition (HD) color in diagnosis and evaluation of symptom severity in CTS. Methods . The study prospectively enrolled 39 wrists from 23 patients with EDT-confirmed CTS, 15 wrists from 12 patients who have CTS symptoms without EDT abnormality and 28 wrists from 14 healthy volunteers. Cross-sectional area (CSA) and longitudinal diameter of median nerve were measured. SWE of median nerve at the wrist and midforearm were performed, and the ratio between them was calculated. SWE of abductor pollicis brevis (APB) and abductor digiti minimi (ADM) were also measured and the ratio was obtained. HD color was conducted in the longitudinal plane at carpal tunnel. Results . The CSA of the median nerve at the carpal inlet and longitudinal diameter were significantly larger for the EDT-confirmed CTS group compared to control group (13.21[11.28,17.23] vs 7.98[6.53,8.94]; p < 0.001, 2.77[2.41,3.08] vs 2.07[1.79,2.24]; p < 0.001). It also had significantly higher median nerve elasticity ratio (2.59[1.77,4.09] vs 1.61[1.32,1.94]; p = 0.007). HD color showed significantly higher grades in the former group (p = 0.004). In ROC analysis, a 1.97 cut-off value on SWE ratio revealed sensitivity, specificity, PPV, NPV of 74.4%, 78.6%, 82.9%, 68.8%, respectively (AUC: 0.796[0.687,0.905]). Inter-rater reliability was excellent for SWE measurements (ICC: 0.908(0.761,0.967)). There was no significant correlation of CSA, elasticity and HD color grade with clinical symptom scores. In comparison between the group of CTS patients without EDT abnormality and control group, the former had significantly larger CSA in carpal inlet and elasticity ratio (9.61[7.21,11.55] vs 7.98[6.53,8.94]; p = 0.011, 2.59[0.94,4.65] vs 1.61[1.32,1.94]; p = 0.009). Conclusion . SWE and HD color are helpful supportive tools in diagnosing CTS, especially in patients who have typical CTS symptoms but normal results in EDT.