Thirty Years of Magnetic Stimulation: Is it Still Only for the Purpose of Research?

Neurophysiological Evaluation of Neural Transmission in Brachial Plexus Motor Fibers with the Use of Magnetic versus Electrical Stimuli

The anatomical complexity of brachial plexus injury requires specialized in-depth diagnostics. The clinical examination should include clinical neurophysiology tests, especially with reference to the proximal part, with innovative devices used as sources of precise functional diagnostics. However, the principles and clinical usefulness of this technique are not fully described. The aim of this study was to reinvestigate the clinical usefulness of motor evoked potential (MEP) induced by a magnetic field applied over the vertebrae and at Erb's point to assess the neural transmission of brachial plexus motor fibers. Seventy-five volunteer subjects were randomly chosen to participate in the research. The clinical studies included an evaluation of the upper extremity sensory perception in dermatomes C5-C8 based on von Frey's tactile monofilament method, and proximal and distal muscle strength by Lovett's scale. Finally, 42 healthy people met the inclusion criteria. Magnetic and electrical stimuli were applied to assess the motor function of the peripheral nerves of the upper extremity and magnetic stimulus was applied to study the neural transmission from the C5-C8 spinal roots. The parameters of compound muscle action potential (CMAP) recorded during electroneurography and MEP induced by magnetic stimulation were analyzed. Because the conduction parameters for the groups of women and men were comparable, the final statistical analysis covered 84 tests. The parameters of the potentials generated by electrical stimulus were comparable to those of the potentials induced by magnetic impulse at Erb's point. The amplitude of the CMAP was significantly higher following electrical stimulation than that of the MEP following magnetic stimulation for all the examined nerves, in the range of 3-7%. The differences in the potential latency values evaluated in CMAP and MEP did not exceed 5%. The results show a significantly higher amplitude of potentials after stimulation of the cervical roots compared to potentials evoked at Erb's point (C5, C6 level). At the C8 level, the amplitude was lower than the potentials evoked at Erb's point, varying in the range of 9-16%. We conclude that magnetic field stimulation enables the recording of the supramaximal potential, similar to that evoked by an electric impulse, which is a novel result. Both types of excitation can be used interchangeably during an examination, which is essential for clinical application. Magnetic stimulation was painless in comparison with electrical stimulation according to the results of a pain visual analog scale (3 vs. 5.5 on average). MEP studies with advanced sensor technology allow evaluation of the proximal part of the peripheral motor pathway (between the cervical root level and Erb's point, and via trunks of the brachial plexus to the target muscles) following the application of stimulus over the vertebrae.

Slow repetitive transcranial magnetic stimulation in refractory juvenile myoclonic epilepsies

OBJECTIVE

The objective of the study was to investigate the effects of slow repetitive transcranial magnetic stimulation (rTMS) on patients with refractory juvenile myoclonic epilepsy (JME).

METHODS

One thousand pulses with the intensity of 120% active motor threshold (AMT) at 0.2 Hz frequency were applied on 5 consecutive days in 10 patients with refractory JME. Sham rTMS was performed after 3 months. Electroencephalography (EEG) examinations were performed before rTMS, on the 5th day, and 1, 2, 4, and 8 weeks after rTMS. Resting motor threshold (RMT), AMT, and cortical silent periods (CSPs) were recorded before the application and at the end of day 5. The changes in the quality of life were evaluated using the Quality of Life in Epilepsy Inventory (QOLIE-31).

RESULTS

No adverse effects were observed. The number of seizures decreased by 29-50%, and interictal discharge durations decreased 2 weeks after the real rTMS. No significant difference was observed between the AMT and RMT values recorded before and after the stimulations. Statistically significant increases in CSP duration and quality of life scores were found following real rTMS. Repetitive transcranial magnetic stimulation may be considered as a safe treatment option in refractory JME.

CONCLUSION

This study provides some positive evidence that rTMS may be effective in resistant JME.