Unilateral repetitive tibial nerve stimulation improves neurogenic claudication and bilateral F-wave conduction in central lumbar spinal stenosis

Abstract

Background

Repetitive electrical nerve stimulation of the lower limb may improve neurogenic claudication in patients with lumbar spinal stenosis (LSS) as originally described by Tamaki et al. We tested if this neuromodulation technique affects the F-wave conduction on both sides to explore the underlying physiologic mechanisms.

Methods

We studied a total of 26 LSS patients, assigning 16 to a study group receiving repetitive tibial nerve stimulation at the ankle (RTNS) on one leg, and 10 to a group without RTNS. RTNS conditioning consisted of a 0.3-ms duration square-wave pulse with an intensity 20% above the motor threshold, delivered at a rate of 5 Hz for 5 min. All patients underwent the walking test and the F-wave and M-wave studies for the tibial nerve on both sides twice; once as the baseline, and once after either the 5-min RTNS or 5-min rest.

Results

Compared to the baselines, a 5-min RTNS increased claudication distance (176 ± 96 m vs 329 ± 133 m; p = 0.0004) and slightly but significantly shortened F-wave minimal onset latency (i.e., increased F-wave conduction velocity) not only on the side receiving RTNS (50.7 ± 4.0 ms vs 49.2 ± 4.2 ms; p = 0.00081) but also on the contralateral side (50.1 ± 4.6 ms vs 47.9 ± 4.2 ms; p = 0.011). A 5-min rest in the group not receiving RTNS neither had a significant change on claudication distance nor on any F-wave measurements. The M response remained unchanged in both groups.

Conclusions

The present study verified a beneficial effect of unilaterally applied RTNS of a mild intensity on neurogenic claudication and bilateral F-wave conduction. Our F-wave data suggest that this type of neuromodulation could be best explained by an RTNS-induced widespread sympathetic tone reduction with vasodilation, which partially counters a walking-induced further decline in nerve blood flow in LSS patients who already have ischemic cauda equina.

Introduction

Repetitive electrical nerve stimulation of the lower limb provides a beneficial effect on neurogenic claudication in patients with lumbar spinal stenosis (LSS). This type of neuromodulation has received little attention since originally described by Tamaki et al. (1986) [1] and confirmed by Takahashi et al. (1988) [2], despite its potential as a useful treatment option for LSS.

More recently (2014) [3], one study reconfirmed this stimulation-induced effect, showing in a series of LSS patients that repetitive tibial nerve stimulation at the ankle (RTNS) at the mild intensity of 5/s for 5 min doubled their maximal walking distances, at which point they could no longer continue walking due to an aggravation in leg symptoms (i.e., absolute claudication distance) [4]. The same study also revealed that conduction velocity of the tibial nerve F-wave significantly increased on the side receiving RTNS in LSS patients, but not in age- and sex-matched healthy subjects, suggesting an RTNS-induced improvement in motor nerve conduction in already impaired LSS patients.

To further clarify this neuromodulation, in the present exploratory study, we investigated whether the effects of RTNS applied to one leg in LSS patients occurred specifically in the stimulated nerve or more extensively in other unstimulated nerves, by conducting the electrophysiological study on both sides. Additionally, we compared the data for the two groups of central LSS patients; RTNS(+) group and RTNS(−) group. We also sought to determine whether RTNS affects the proximal motor segment, the distal motor segment, or both, by comparing the latency changes of F-wave vs M-wave induced by RTNS.