High-resolution sonography versus EMG in the diagnosis of carpal tunnel syndrome

Background: Carpal tunnel syndrome (CTS) is a common entrapment neuropathy. Electrodiagnostic testing (EMG) is used to confirm the diagnosis. It is not known what the diagnostic accuracy of high-resolution sonography is in comparison to EMG. Objective: The aim of this study was to compare the diagnostic accuracy of both tests in CTS patients. Methods: A prospective cohort of 207 patients with possible CTS underwent high-resolution sonography and EMG. The diagnosis of CTS was based on clinical signs and symptoms. The cross-sectional area of the median nerve at the carpal tunnel inlet and at the distal one-third level of the forearm was assessed by an investigator, blinded to the clinical and EMG data. Normal sonographic values were obtained from 137 controls. All patients and 40 controls underwent a standardised nerve conduction study. The kappa coefficient was used to evaluate the relationship between sonography, EMG and clinical diagnosis. Results: The cross-sectional area at the distal one-third of the forearm was not significantly different between the controls and patients (p= 0.59), whereas the cross-sectional area at the carpal tunnel inlet was significantly increased in the patient group (p<0.0001). The kappa coefficient for EMG using the median-ulnar distal sensory latency difference versus clinical evaluation was 0.64 and, for sonography, this coefficient was 0.69; these were not statistically different (p= 0.37). Combining the two tests resulted in a kappa coefficient of 0.72, which was not significantly different from sonography alone (p= 0.73). Conclusion: In patients with a clinical diagnosis of CTS, the accuracy of sonography is similar to that for EMG. Sonography is probably preferable because it is painless, easily accessible and preferred by the patients.