Comparative analysis of excitability of radicular and intramuscular axonal systems in healthy volunteers during peripheral magnetic stimulation

Background. Peripheral magnetic stimulation (PMS) is applied over spinal roots, peripheral nerves, terminal motor nerve branches. PMS has been used as a method of diagnosis and treatment for two decades. Despite the considerable amount of PMS studies, there is no consensus on the approach to determine the intensity of the magnetic stimulus in the treatment stimulation, the need for the differentiated activation of the different parts of the peripheral nervous system. This was the prerequisite for carrying out this study.  Objective: to investigate the PMS intensity required to activate spinal roots and terminal nerve branches, the second object was the comparison of the threshold values among volunteers. Materials and methods. Thirty four healthy subjects with no neuromuscular diseases were enrolled in the study (mean age 31.0 ± 8.6 years). PNS was applied by Magstim 200 magnetic stimulator (Great Britain). During the research the subjective threshold, the threshold of muscle contraction, the threshold of the root activation (according to motor evoked potential) were estimated. Stimulation-induced muscle activity was recorded via surface EMG system (Neurosoft, Russia) synchronized with the magnetic stimulator. Results. The analysis of data identified the significant differences (p <0.05) between the root activation and terminal nerve branches threshold values. There were no reports of gender differences between the threshold values of all investigated parameters within the group (p >0.05). There were no significant differences between right and left limbs (p >0.05) in the comparison of all parameters. Conclusion. The results of the present study can indicate the possibility of the individual approach of the determination the intensity of the magnetic stimulus for each patient. The findings of our study provide an opportunity for a better understanding of the action mechanism of PMS and can be used in order to develop the treatment algorithm for the use in the clinical settings.

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