Predictors of Normal Electrodiagnostic Testing in the Evaluation of Suspected Carpal Tunnel Syndrome

Abstract

Electrodiagnostic studies (electromyography and nerve conduction velocity; EMG/NCV) are used to confirm the diagnosis of carpal tunnel syndrome (CTS) and to evaluate its severity. We investigated the hypothesis that normal electrodiagnostic median nerve testing is predicted by 1) Physician pre-test confidence in the diagnosis of CTS, and 2) Puzzling patient factors. One hundred and forty consecutive patients who underwent electrodiagnostic testing to evaluate for possible CTS were reviewed retrospectively. Both physician confidence in the diagnosis of CTS and puzzling patient factors (heightened illness concern, disproportionate complaints, and vague/nonanatomical/noncharacteristic symptoms) were recorded. Electrodiagnostic testing was used as the reference standard for diagnosis of CTS. Electrodiagnostic testing confirmed CTS in 115 patients and was within normal limits in 25 patients. Low physician confidence in the diagnosis of CTS was highly predictive of a normal electrodiagnostic test (p<0.001), with high sensitivity (97%), moderate specificity (40%), and high overall accuracy (87%). Puzzling patient factors were moderately predictive of normal electrodiagnostic testing (p < 0.001), with low sensitivity (16%), high specificity (96%), and high overall accuracy (81%). The best multivariable model retained younger age, negative Phalen's test, and low physician confidence as the best predictors of normal electrodiagnostic testing and explained 35% of the variation in test results. A model with low confidence alone explained 19% of the variation in test results. Physician intuition as recorded in the medical record in terms of puzzlement and low confidence are very specific and accurate predictors of normal electrodiagnostic testing in the setting of suspected carpal tunnel syndrome.

Comparison of Borderline Ultrasound and Nerve Conduction Studies for Carpal Tunnel Syndrome

“…The cutoff value used for the CSA of the median nerve as measured by US was 10 mm 2 . 7,11,12 The 10% upper and lower margins of the cutoff values used can be seen in Table 1.…”

Hand examination and investigations

“…44,45 Neuropathic pain: diagnostic blocks Diagnostic blocks are used to obtain information about the source of a patient's pain. As such they differ in principle and in practice from regional anaesthetic blocks.…”

Patient-Reported Disability Measures Do Not Correlate with Electrodiagnostic Severity in Carpal Tunnel Syndrome

“…Although history and physical alone can be sufficient to diagnose carpal tunnel syndrome (CTS), electrophysiologic studies including electromyography and nerve conduction studies (EMG/NCS) continue to play an important role in the evaluation of this condition. 1 – 3 Electrodiagnostic findings have been compared with a number of specific symptom scoring tools, including the CTS Assessment Questionnaire, 4 , 5 CTS-6 scale, 6 and the McGill pain questionnaire. 7…”