Abstract
BACKGROUND: Electrodiagnostic studies (EDS) have little diagnostic value when the probability of carpal tunnel syndrome (CTS) is high. Ultrasound (US) is useful for diagnosing CTS, but its effect on the diagnostic probability of CTS has not been well studied. The purpose of this study was to evaluate the change in probability of CTS following EDS and US. It was hypothesized that EDS and US would be of low diagnostic value for patients with a high CTS-6 (6-Item Carpal Tunnel Syndrome Questionnaire) score. METHODS: A cohort of patients with 295 extremities being assessed for compressive neuropathies of the upper extremity was prospectively evaluated using CTS-6, EDS, and US. The pretest probability of CTS was calculated using CTS-6. Bayesian analysis was used to calculate the posttest probability following EDS and US. Correlation, change in probability, and between-group differences were calculated. RESULTS: For all patients, there was a mean increased change in probability of CTS following EDS testing. The mean probability of CTS increased with pretest probability <.5; this effect was magnified in patients with diabetes. All patients with CTS-6 of 8 to 12 had a change in probability >10% following EDS and US, but with CTS-6 >17, a change >10% was seen in no patients following EDS and in 15% following US. CONCLUSIONS: Adjunct testing is of greatest diagnostic value for patients with CTS-6 of 8 to 12. For patients with CTS-6 >17, adjunct testing is of little diagnostic value, but if additional testing is chosen, US may be of greater value than EDS.