Application of magnetic motor stimulation for measuring conduction time across the lower part of the brachial plexus^[*]

Abstract

Objective The objective of this study was to calculate central motor conduction time (CMCT) of median and ulnar nerves in normal volunteers. Conduction time across the lower part of the brachial plexus was measured by using magnetic stimulation over the motor cortex and brachial plexus and recording the evoked response in hand muscles.

Design This descriptive study was done on 112 upper limbs of healthy volunteers. Forty-six limbs belonging to men and sixty-six belonging to women were studied by magnetic stimulation of both motor cortex and brachial plexus and recording the evoked response in thenar and hypothenar muscles. Stimulation of the motor cortex gives rise to absolute latency of each nerve whereas stimulation of the brachial plexus results in peripheral conduction time. The difference between these two values was considered the central motor conduction time (CMCT).

Results In summary the result are as follows; Cortex-thenar latency = 21.4 ms (SD = 1.7), CMCT-thenar = 9.6 ms (SD = 1.9), Cortex-hypothenar latency = 21.3 ms (SD = 1.8), CMCT-hypothenar = 9.4 ms (SD = 1.8).

Conclusion These findings showed that there is no meaningful difference between two genders. CMCT calculated by this method is a little longer than that obtained by electrical stimulation that is due to the more distally placed second stimulation. We recommend magnetic stimulation as the method of choice to calculate CMCT and its use for lower brachial plexus conduction time. This method could serve as a diagnostic tool for diagnosis of lower plexus entrapment and injuries especially in early stages.

^*This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

• References

• 1 Dumitru D, Amato AA, Zwarts M. Electrodiagnostic Medicine. Hanley & Belfus; Philadelphia: 2002. Chapter 10. 415-428
• 2 Lefaucheure JP. Transcranial magnetic stimulation: applications in neurology. Revue Neurology 2005; 161 (11) 1121-30
• 3 Brostrom S. Magnetic evoked responses from pelvic floor. Neurology and Urodynamics 2003; 72 (7) 620-37 10.1002/nau.10151
• 4 Hess CW, Mills KR, Murray NMF, Schriefer TN. Magnetic brain stimulation: Central motor conduction studies in multiple sclerosis. Annal of Neurology 1987; 22 (6) 744-52 10.1002/ana.410220611
• 5 Baker AT, Jalnous R, Freeston IL. non-invasive magnetic stimulation of human motor cortex. Lancet 1985; 1: 1106-1107 10.1016/S0140-6736(85)92413-4 2860322
• 6 Attarian S, Verschuefen A, Pouget J. Progression of cortical and spinal dysfunctions over time in amyotrophic lateral sclerosis. Muscle and Nerve 2007; 36 (1) 55-61 10.1002/mus.20789
• 7 Claus D. Central motor conduction: Method and normal results. Muscle and Nerve 1990; 13 (12) 1125-32 10.1002/mus.880131207
• 8 Kimura J. Electrodiagnosis in diseases of nerve and muscle. F. A. Davis Company; Philadelphia: 1989
• 9 Hallet M. Transcranial magnetic stimulation: A useful tool for clinical neurophysiology. Annal of Neurology 1996; 40 (3) 344-345 10.1002/ana.410400303
• 10 Samii A, Luciano CA, Dambrosia JM, Hallett M. central motor conduction time, reproducibility and discomfort of different methods. Muscle Nerve 1998; 21: 1445-1450 10.1002/(SICI)1097-4598(199811)21:11<1445::AID-MUS12>3.0.CO;2-# 9771668
• 11 Zwarts MJ. Central motor conduction in relation to contra and ipsilateral activation. Electromyography and Clinical Neurophysiology 1992; 425-429 10.1016/0168-5597(92)90057-I
• 12 Eisen AA, Shtybel W. clinical experience with transcranial magnetic stimulation. Muscle Nerve 1990; 13: 995-1011 10.1002/mus.880131102 2233862