[Preliminary study of motor evoked potential (MEP) on facial nerve palsy]

Motor evoked potential (MEP) examination is a new method. Ipsilateral facial muscles are excited by magnetic stimulation over the scalp when the coil is placed on the parieto-occipital region. Using magnetic stimulator and EMG instrument (1500C4 DISA), one can measure the CMAPs from orbicularis oris and frontal muscle. In 30 normal subjects, the CMAPs were found to be similar in form but of longer latency than those obtained with electrical stimulation (ENoG). In 20 patients with facial nerve paralysis due to Bell's palsy, Hunt's syndrome or trauma, the latencies on the affected sides were apparently longer and the amplitudes much lower than those in normal ones. Our studies imply that magnetic stimulation can be used to detect facial nerve in the region inside the temporal bone which is not accessible by electrical stimulation. Using ENoG and MEP methods, the proximal facial nerve conduction can be measured somewhat quantitatively, thus one can detect conduction block or axonal degeneration early. It is important not only for the diagnosis but also for the treatment and evaluation of prognosis.