The lack of a gold standard is the fundamental problem in diagnosing CTS. The objective of this study was to evaluate the utility and appropriate use of CSI in diagnosing mild CTS.

CTS accounts for 90% of neuropathies, with a prevalence of ~270/100,000. Diagnosis is based on clinical complaints, neurologic examination, provocative maneuvers, and electrodiagnostic studies. Treatment is conservative or surgical depending on severity of symptoms. CTS is the most common reason for EMGs in most labs and the most common EMG finding. NCS/EMG is helpful in diagnosing CTS, providing objective information regarding the median nerve's physiologic health and degree of damage. The efficacy of CSI has been debated as a confirmatory test.

This is a retrospective, multi-center case series of 69 limb studies in 57 patients who were evaluated between July 2021 and  June 2022 who underwent NCS/EMG and CSI testing to evaluate for mild CTS. Median nerve peak/distal latencies, conduction velocities, SNAPs, CSI parameters (median-radial latency comparison of digit I, median-ulnar latency comparison of digit IV, and trans-palmar median-ulnar latency comparison), and provocative maneuvers (Tinel’s and Phalen’s) were included. Patients who have abnormal NCS or who did not complete full CSI were excluded.

There was no correlation between normal CTS studies and a positive CSI. Tinel’s testing was nonspecific and nonsensitive with low PPV/NPV. Phalen’s testing had a relatively high specificity, but low sensitivity and low PPV/NPV. There was a relatively high correlation of positive CSI studies when each portion was performed in this population. 27/69 CSI’s were abnormal in this study. The overall yield was ~39%