Application of Median-Ulnar F-Wave Latency Difference for the Diagnosis of Carpal Tunnel Syndrome

Abstract

Background and Objective: Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy in which the median nerve is compressed in the wrist area while it passes through it, and its early diagnosis will improve the overall outcome and reduce morbidity. Electrodiagnostic testing is the most commonly used techniques to diagnose it but no consensus is reached about which test is the most useful. This research was conducted to evaluate the sensitivity and specificity of the difference in F-wave conduction velocity below and above carpal tunnel for the diagnosis of CTS. Methods: This case-control study included 240 patients clinically diagnosed with CTS with negative nerve conduction test, and these tests included the F-wave conduction velocity of median nerve by stimulating the nerve at two sites, one at mid-palm and the other at the wrist (6 cm proximal to mid-palm stimulation site). After that, distance from stimulating sites to the area between C7 vertebral spine was obtained and the resulting two conduction velocities were compared. Findings: The difference in F-wave conduction velocity across the wrist was 4.9±1.6 m/s in patients with CTS while it was 2±0.1 m/s in healthy control subjects, with statistically significant differences (p<0.05). Also, the study found that at difference of 3 m/s between wrist and mid-palm stimulation, the sensitivity for diagnosing CTS was 90% and specificity was 100%. Conclusion: The results of this study showed that F-wave conduction velocity of median nerve difference across the wrist is a new technique to test median nerve in CTS and it is highly sensitive and specific.

Keywords

• median nerve
• nerve conduction studies
• wrist injuries
• carpal tunnel syndrome.