Repetitive Peripheral Magnetic Nerve Stimulation (rPMS) as Adjuvant Therapy Reduces Skeletal Muscle Reflex Activity

Abstract

Background: The reduction of muscle hypertonia and spasticity, as well as an increase in mobility, is an essential prerequisite for the amelioration of physiotherapeutical treatments. Repetitive peripheral magnetic nerve stimulation (rPMS) is a putative adjuvant therapy that improves the mobility of patients, but the underlying mechanism is not entirely clear. Methods: Thirty-eight participants underwent either an rPMS treatment (N = 19) with a 5 Hz stimulation protocol in the posterior tibial nerve or sham stimulation (N = 19). The stimulation took place over 5 min. The study was conducted in a pre-test post-test design with matched groups. Outcome measures were taken at the baseline and after following intervention. Results: The primary outcome was a significant reduction of the reflex activity of the soleus muscle, triggered by a computer-aided tendon-reflex impact. The pre-post differences of the tendon reflex response activity were -23.7% (P < 0.001) for the treatment group. No significant effects showed in the sham stimulation group. Conclusion: Low-frequency magnetic stimulation (5 Hz rPMS) shows a substantial reduction of the tendon reflex amplitude. It seems to be an effective procedure to reduce muscular stiffness, increase mobility, and thus, makes the therapeutic effect of neuro-rehabilitation more effective. For this reason, the 5 Hz rPMS treatment might have the potential to be used as an adjuvant therapy in the rehabilitation of gait and posture control in patients suffering from limited mobility due to spasticity. The effect observed in this study should be investigated conjoined with the presented method in patients with impaired mobility due to spasticity.

Keywords: cerebral palsy; magnetic stimulation; muscle hypertonia; muscle spasticity; pain; reflex.

Figure 1

The sketch shows the subject had a fixed sitting position. The subjects were seated comfortably upright, with a knee angle and a foot angle each of 90°. The left foot was fixed with two stirrups on a tempered (30°C) footplate. The upper leg was secured at the topside; the arm and head positions were kept constant during the whole experiment. The reflex-triggering hammer (right side) was equipped with a force sensor, in order to record the impact forces at the muscle-Achilles tendon-complex.

Figure 2

A raw data set of one subject shows the effect of before (left) and after (right) the rPMS. Each graph shows 15 peak-to-peak superimposed compound muscle action potential (CMAP_pp) curves that were induced by a reflex hammer impact on the Achilles tendon. Mean CMAP_pp amplitudes were ~4.2 mV at baseline and ~3.5 mV after the rPMS in this subject.

Figure 3

Changes in the compound muscle action potential (CMAP_pp) size before the repetitive peripheral magnetic stimulation (rPMS) and post stimulation. The dashed line represents the control group (CG) and the continuous line indicates the treatment group (CG). Each bar corresponds to the SD value. Note that the reflex responses significantly decreased in size only after the rPMS in the treatment group. ***Denotes a significant difference between pre- and post-test (***P ≤ 0.001) in CG.

Figure 4

The diagram shows the spinal circuitry that was possible involved γ-motor neurons (γ-MN), α-motor neurons (α-MN), Ia afferents (Ia), Ib afferents (Ib), or presynaptic mechanism (PSI), by near-muscle magnetic nerve stimulation. However, at this time, no conclusions can be reached about the mode of action of the magnetic stimulation on the spinal neuronal structures.