Value of F-wave studies on the electrodiagnosis of carpal tunnel syndrome

BACKGROUND F waves are late electrophysiological responses to antidromic activation of motor neurons and are used to evaluate the conduction along the whole length of peripheral nerves. We aimed to determine the diagnostic efficacies of minimum median nerve F-wave latency (FWL) and median-to-ulnar nerve F-wave latency difference (FWLD) on carpal tunnel syndrome (CTS). MATERIALS AND METHODS The electrophysiological studies consisted of sensory and motor nerve conduction and F-wave studies of the median and ulnar nerves. The best cut-off points of minimum median nerve FWL and FWLD for the diagnosis of CTS were detected for the whole study group and for different height subgroups (Group 1: 150-159 cm, Group 2: 160-169 cm, and Group 3: over 170 cm). The diagnostic efficacies of minimum median nerve FWL and FWLD were calculated for the whole CTS group and for the mild CTS group, separately. RESULTS The best cut-off point of minimum median nerve FWL on the diagnosis of CTS was determined as 24.60 ms for the whole group. It was 23.90 ms for Group 1, 24.80 ms for Group 2, and 28.40 ms for Group 3. The usage of these stratified cut-off points yielded a higher total diagnostic efficacy rate than single cut-off point usage (79.9% vs 69%, respectively; P=0.02). The best cut-off point of FWLD on the diagnosis of CTS was 0.80 ms for the whole group. It was 0.55 ms for Group 1, 0.30 ms for Group 2, and 0.85 ms for Group 3. Both the single cutoff point usage and the stratified chart usage for FWLD had equal diagnostic efficacy (85.1%). In the mild CTS group, diagnostic efficacy was 55.5% for minimum median nerve FWL and 78.8% for FWLD (P=0.0001). CONCLUSION Median-to-ulnar nerve FWLD yields a higher diagnostic efficacy than minimum median nerve FWL on the diagnosis of CTS. However, the sensitivities of both parameters are not satisfactory for the extremities with mild CTS, which compose the main group having diagnostic challenge.