Background/Purpose: Routine use of sonography for the diagnosis of carpal tunnel syndrome (CTS) is hampered by the lack of consensus regarding anatomical landmarks for the measurement of median nerve volume and difficulty of determining thresholds for abnormal median nerve swelling. This study was conduced to compare ultrasound measurement of median nerve cross-sectional area (CSA) at different anatomical landmarks and to analyze the value of Power Doppler (PD) signals within the median nerve

Methods: We prospectively studied 135 consecutive patients with suspected CTS undergoing clinical and electrophysiological evaluation at two subsequent visits within three months. Final diagnosis of CTS was established by the evaluating neurologist based on findings from these conventional methods at both visits. Median nerve sonography was performed by two rheumatologists using a GE Logiq E9. CSA was measured at 5 different levels at forearm and wrist; and CSA wrist to forearm ratios or differences were calculated. Intra-neural PD-signals were semiquantitatively graded (scale 0–3). Diagnostic values of different ultrasound methods were compared by receiving operating characteristic (ROC) curves using SPSS (v19.0).

Results: CTS was diagnosed in 111 (45.5%) wrists; 84 (34.4%) had no CTS and 49 (20.1%) were possible CTS cases. Diagnostic values were comparable for all sonographic methods to determine median nerve swelling with AUCs ranging from 0.75 to 0.84. Thresholds of 9.8 and 13.8 mm2 for the largest CSA of the median nerve yielded a sensitivity of 91% and a specificity of 92%, respectively. In cases of mild median nerve swelling the relative increase in CSA between the entrapment area and forearm provided additional diagnostic certainty (AUCs from 0.60 to 0.67). Increased vascularity as indicated by a PD-score ≥2 had a specificity of 90% for the diagnosis of CTS. Reliability of sonographic median nerve volumetry was good as indicated by an intra-class correlation coefficient of 0.90 (95% CI: 0.79-0.95).

Conclusion: Sonographic assessment of median nerve swelling and tissue vascularity at different anatomical landmarks allows for a reliable confirmation of the diagnosis in patients with clinically suspected CTS

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ultrasound-for-diagnosis-of-carpal-tunnel-syndrome-comparison-of-different-methods-to-determine-median-nerve-volume-and-value-of-power-doppler-sonography/