A study of F-waves in patients with unilateral lumbosacral radiculopathy

Background and purpose:  The F wave, a late response of low amplitude, is widely used in the study of peripheral nerve lesions, and its persistence and latencies are the main parameters that are usually considered. The analysis of repeater F-waves, which are commonly observed in association with focal or generalized motor neuropathy, is not always performed as a standard electrodiagnostic protocol.
Methods:  We recorded and quantified the F waves from 13 healthy subjects and 22 patients with unilateral lumbosacral radiculopathy (ULSR) affecting the L5 or S1 roots.
Results:  We found differences between the injured and normal sides of patients with ULSR in several F-wave parameters. Taking into consideration the normalized and pooled values of tibial and peroneal nerves in the injured side of patients with ULSR, the minimum and mean latencies were higher (1.05 and 1.04 with respect to 1.00; P  <   0.01), the relative amplitude of the F waves was higher (1.95 with respect to 1.00; P  <   0.001), and the percentage of repeater F-waves was also higher (4.19 with respect to 1.00; P  <   0.001). This latter parameter was the most sensitive to detect lateral differences as indicated by the percentage of change and its high z score.
Conclusions:  Our results show that the use of F-waves may improve the electrodiagnosis of the ULSR if the number of repeater waves is evaluated given the clear and consistent increase of this variable in patients with lumbosacral root injury.