Diagnostic Value of Cross-Sectional Area of Median Nerve in Grading Severity of Carpal Tunnel Syndrome

Carpal tunnel syndrome is a common peripheral entrapment neuropathy. The purpose of this study is to determine whether high resolution ultrasonography can be an alternative diagnostic method to nerve conduction study in grading the severity of carpal tunnel syndrome. A total of 164 wrists of 82 patients, bilaterally, were enrolled in the study. The cross-sectional area of the median nerve at the carpal tunnel inlet and outlet was measured in all patients with electrophysiologically confirmed carpal tunnel syndrome. All patients had nerve conduction study performed one week before ultrasonography. Then, comparisons between ultrasonography and nerve conduction study were made. The grading severity according to nerve conduction study was used as a gold standard reference. The mean median nerve cross-sectional area at the tunnel inlet was11.4±1.7 mm2 for the carpal tunnel syndrome affected wrist and 5.78±0.9 mm2 for the normal wrist (P<0.001). The mean median nerve cross-sectional area at the tunnel outlet was 9.9±1.2 mm2 for the affected wrist with carpal tunnel syndrome and 4.7±0.7 mm2 for the normal wrist (P<0.001).The best cutoff value of cross-sectional area at the tunnel inlet and outlet was 8.5 mm2.The difference in cross-sectional area of the median nerve in mild, moderate and severe carpal tunnel syndrome was not statistically significant (P=0.2) neither in the carpal tunnel inlet nor outlet. Based on this study, cross-sectional area of median nerve ultrasonography has a diagnostic value to confirm or exclude carpal tunnel syndrome, but could not be used for grading its severity.