Borderline Nerve Conduction Velocities for Median Neuropathy at the Carpal Tunnel

Purpose Patient knowledge of the frequency with which electrodiagnostic testing (EDx) for suspected median neuropathy at the carpal tunnel addresses nuance in the distinction between normal and abnormal neurophysiology might help them make an informed decision about whether or not to have this test. We reviewed a large set of consecutive EDx for possible carpal tunnel syndrome (CTS) and associated medical records to determine (1) the percentage of EDx measurements within 10% of threshold values; (2) discordance between clinician and EDx diagnosis of CTS using diagnostic performance characteristics; and (3) demographic and disease characteristics independently associated with EDx diagnosis of median neuropathy at the carpal tunnel. Methods We retrospectively reviewed nerve conduction study (NCS) results of 537 consecutive patients evaluated for possible idiopathic median neuropathy at the carpal tunnel. We measured the number of patients within 10% of 3 NCS diagnostic thresholds; the diagnostic performance characteristics comparing clinician and EDx diagnosis; and patient and disease characteristics associated with EDx diagnosis of CTS. Results The 3 NCS parameters were within 10% of the threshold for diagnosis of median neuropathy at the carpal tunnel in 2.6% to 33% of patients. Overall, 76% of EDx results were interpreted as median neuropathy at the carpal tunnel, 19% as normal, and 5% as another diagnosis (eg, cervical radiculopathy). Patients with normal EDx were significantly younger, more likely not to report paresthesias/numbness, more likely to have prior normal EDx, and less likely to have had a previous contralateral carpal tunnel release. Conclusions This data set reflecting management strategies for suspected CTS at a large institution confirms inherent diagnostic uncertainty, relatively strong concordance between clinician and EDx diagnosis, and the importance of focusing on paresthesia rather than pain. These findings support the use of clinical prediction rules and may help inform a patient’s decision regarding whether or not to have EDx. Type of study/level of evidence Diagnostic III.