Comparison of ultrasound and electrodiagnostic testing for diagnosis of carpal tunnel syndrome: study using a validated clinical tool as the reference standard.

BACKGROUND: Ultrasound examination is both accurate and cost-effective for the confirmation of a clinical diagnosis of carpal tunnel syndrome. Previous studies have shown electrodiagnostic testing and ultrasound to be similar with regard to sensitivity and specificity. The purpose of this study was to compare the sensitivity and specificity of ultrasound and electrodiagnostic testing by using a validated clinical diagnostic tool as the reference standard.

METHODS: All consecutive patients referred to an upper-extremity practice for electrodiagnostic testing for any reason over a three-month period were recruited to participate in this study. All patients were evaluated with the use of the Carpal Tunnel Syndrome 6 (CTS-6) clinical diagnostic tool, and a score of ≥12 was considered positive for carpal tunnel syndrome. A positive finding on ultrasound was considered to be a cross-sectional area of the median nerve, measured just proximal to the level of the pisiform, of ≥10 mm(2). A positive finding on electrodiagnostic testing was a distal motor latency of ≥4.2 ms and/or a distal sensory latency of ≥3.2 ms. Sensitivity, specificity, and accuracy were calculated for ultrasound and electrodiagnostic testing with use of the CTS-6 as the reference standard.

RESULTS: With use of the CTS-6 as the reference standard, ultrasound had a sensitivity of 89% and a specificity of 90% in our series of eighty-five patients. Electrodiagnostic testing had a sensitivity of 89% and a specificity of 80%. The positive predictive value of ultrasound was 94% compared with 89% for electrodiagnostic testing. The negative predictive value of ultrasound was 82% compared with 80% for electrodiagnostic testing. Ultrasound was accurate in seventy-six (89%) of the eighty-five cases whereas electrodiagnostic testing was accurate in seventy-three (86%) of the eighty-five cases (p = 0.5).

CONCLUSIONS: While ultrasound will not replace electrodiagnostic testing in complicated or unclear cases, in a select group of patients with a positive CTS-6, ultrasound can be used to confirm the diagnosis of carpal tunnel syndrome with better specificity and equal sensitivity as compared with those of electrodiagnostic testing.

LEVEL OF EVIDENCE: Diagnostic Level I. See Instructions for Authors for a complete description of levels of evidence.