A comparison of the benefits of sonography and electrophysiologic measurements as predictors of symptom severity and functional status in patients with carpal tunnel syndrome

Objectives: To clarify whether sonography or electrophysiologic testing is a better predictor of symptom severity and functional status in carpal tunnel syndrome (CTS) and to assess the diagnostic value of sonography in patients with idiopathic CTS. Design: Cross-sectional. Setting: University hospital physical medicine and rehabilitation clinic. Participants: Thirty-four hands with CTS and 38 normative hands were evaluated. Interventions: Not applicable. Main Outcome Measures: The Boston Carpal Tunnel Questionnaire, which comprised symptom severity and functional status scale, was applied to CTS patients. Bilateral upper-extremity nerve conduction studies of median and ulnar nerves and sonographic imaging of the median nerve were performed in all participants. Sonographic evaluation was performed by a physician blinded to the physical and electrophysiologic findings of the subjects. Results: Cross-sectional areas (CSAs) of the median nerve at the carpal tunnel entrance and proximal carpal tunnel were 12.5 +/- 2.6 and 10.6 +/- 2.6 versus 15.6 +/- 4.2 and 11.5 +/- 3.2 in CTS patients versus controls, respectively. Increased CSA of the median nerve at the carpal tunnel entrance (P<.002) and at the proximal carpal tunnel (P<.000) were detected in the hands with CTS. Flattening ratios did not differ in a statistically significant manner between the groups (P>.05). The best predictor of symptom severity was median nerve sensory distal latency and that of functional status was median nerve motor distal latency. The optimum cutoff value for median nerve CSA was 11.2mm(2) at the carpal tunnel entrance and 11.9mm(2) at the proximal carpal tunnel. Sensitivity, specificity, and positive and negative predictive values at the proximal carpal tunnel (88%, 66%, 71%, 80%, respectively) were higher than those at the carpal tunnel entrance (68%, 62%, 65%, 66%, respectively). Conclusions: The best predictors of symptom severity and functional status in idiopathic CTS seem to be the electrophysiologic assessments rather than sonographic measurements. On the other hand, sonography may be helpful in the diagnosis of idiopathic CTS.