Ultrasonography in carpal tunnel syndrome: comparison with electrophysiological stage and motor unit number estimate

The purpose of this study was to document the ultrasonographic measurement differences in median nerve size between patients with carpal tunnel syndrome (CTS) and controls, and to correlate these findings with electrophysiological stage and motor unit number estimation (MUNE), thereby allowing us to test the validity of ultrasound as a diagnostic modality for assessing the severity of CTS. High-resolution sonography and electrophysiological studies were performed on 41 wrists of 27 patients and compared with findings on 40 wrists of 20 healthy individuals. On ultrasonographic views, cross-sectional area and flattening ratio in proximal, middle, and distal tunnel segments of the median nerve were measured both by calculating ellipsoid area by large and small cross-sectional diameters and by automated ellipsoid area calculation. We compared electrophysiological stage and MUNE with proximal, middle, and distal cross-sectional area and other ultrasonographic findings. All correlations between electrophysiological stage and cross-sectional areas in these different segments of the median nerve were significant with both measurement methods. Negative correlations were seen between MUNE and cross-sectional area in the proximal and middle segments, whereas no significant correlation was detected in the distal segment. Our results indicate that there are close correlations between the ultrasonographic findings and electrophysiological stage. Ultrasound also reflects the reduction in the number of axons estimated by the MUNE method. Therefore, we suggest that the ultrasonographic findings reflect the severity of disease in patients with CTS.