Suspected carpal tunnel syndrome: Do nerve conduction study results and symptoms match?

To evaluate the diagnostic utility of nerve conduction studies (NCSs) by examining a population with a high pretest probability of carpal tunnel syndrome (CTS), including bilaterally and unilaterally symptomatic patients.

Comparison of the results of NCSs with the results of prospective, pre-NCS, self-administered questionnaires of patients with clinical diagnoses of CTS referred for confirmatory NCSs.

A tertiary care hospital neuro-electrophysiology laboratory.

The study population consisted of 211 patients, 156 (73.9%) of whom were female. Population mean (range) age was 46.7 (21 to 88) years. Mean (range) symptom duration was 29.3 (1 to 300) months.

Patient-reported symptom localization and NCS results.

Results of NCSs were normal in 83 (39.3%) patients, were consistent with CTS in 121 (57.3%) patients, and suggested non-CTS abnormalities in 7 (3.3%) patients. Bilateral symptoms were reported by 139 (65.9%) patients, and isolated unilateral symptoms were reported by 72 (34.1%) patients. Those reporting bilateral symptoms had the highest agreement with NCS results at 38.8%. Unilateral NCS abnormalities were seen in 18.0% of those reporting bilateral hand symptoms. Discordant findings, either bilateral or opposite-side neuropathies, were seen in 25.6% of those reporting isolated right-sided symptoms, and in 55.2% of those reporting isolated left-sided symptoms. Based on these data the sensitivity of the NCS results was 49.1%, with a specificity of 62.5%. The positive predictive value was 86.4%, and the negative predictive value was 20.2%. Overall accuracy was 51.4%. Likelihood ratios were 1.3 with positive results, and 0.8 with negative results.

In our study population NCS results did little to alter the pretest probability of CTS. Physicians using NCSs for verification of clinical diagnosis should be aware of potential limitations.