T110. Visualization of nerve impulse traveling along the brachial plexus after ulnar nerve stimulation using magnetoneurography system

Abstract

Introduction In somatosensory evoked potential (SEP) testing, an analysis of Erb’s potentials following median or ulnar nerve stimulation at the wrist may be useful to define a lesion of the lateral cord or the medial cord of the brachial plexus (BP) neuropathy. However, there have been few SEP studies on multiple site recording of Erb’s potentials so that traveling nature of the nerve impulse along BP has not been visualized yet. By analysis of magnetoneurogram with superconducting quantum interference device (SQUID) sensor system, we succeeded in visualizing the nerve impulse traveling along BP and then propagating into the C5–C8 intervertebral foramen after median nerve stimulation. Here we aimed to analyze the nerve impulse traveling along BP following ulnar nerve stimulation at the wrist. Methods Magnetoneurogram over BP of 5 healthy volunteers (Age range, 25–45 years; mean, 32.8 y.o) were measured after ulnar nerve stimulation (supramaximal stimulus; 5 Hz and averaging 2000 responses) using a newly developed 132 channel SQUID biomagnetometer with an X-ray imaging system (RICOH COMPANY, Ltd., Tokyo, Japan). At the same time, SEP was measured at Erb’s point using MEB-2300 (Nihon Kohden Corporation, Tokyo, Japan) for making sure to deliver supramaximal stimulation. After magnetoneurogram recording, evoked action currents were computationally reconstructed by a spatial filter method and the estimated electric currents map was superimposed over X-ray images. Results We were able to record the magnetic fields over the brachial plexus with good signal quality after ulnar nerve stimulation. Distribution of neural activity currents in the brachial plexus were estimated from the measured magnetic fields and visualized over X-ray images in all subjects. The currents distribution showed axonal activity pattern and passed medially to the coracoid process, crossed the clavicle, and reached the C7 - Th1 intervertebral foramen along the nerve path in the period between 8.0 ms and 13.0 ms after the stimulation. The conduction velocity calculated using the peak latency of the estimated current waveform on the nerve path was 67.13 ± 1.96 m/s. Conclusion By analysis of magnetoneurogram with participants’ X-ray image of the upper thorax,we succeeded in visualizing the nerve impulse traveling along (possibly) the medial cord of BP and then propagating into the C7 – Th1 intervertebral foramen after ulnar nerve stimulation at the wrist. Together with our previous study on magnetoneurogram after median nerve stimulation, we consider magnetoneurogram testing as superior to conventional SEP for analyzing the conductive function of BP because the former enables us to evaluate the conductive function of the nerve from the lateral or medial cord of BP to C5 – Th1 intervertebral foramen after median or ulnar nerve stimulation. We propose that the method of magnetoneurograph with the X-ray image can provide useful information for the non-invasive diagnosis of localization of conduction block in BP neuropathy.