Investigation of Facial Nerve with the Response to Magnetic & Electrical Stimulation and Clinical Application

ABSTRACT

We studied 54 normal volunteers and 30 patients with Bell's palsy by magnetically and electrically evoked direct stimulations of facial nerve. A magnetic coil was placed tangentially to the parieto-occipital area and the stylomastoid foramen. Magnetic stimulation (MS) was less painful and able to excite deeper tying neural structures. Magnetically and electrically evoked direct stimulations of facial nerve showed the same characteristics in excitability and nerve conduction, but they could not be evaluated on the basis of the same normative data. We identified a locus of the impulse generation that might be closer to the exit of facial nerve from the brainstem. Compared with normal controls, MS-evoked CMAPS of patients with Bell's palsy had no responses, longer latencies, lower amplitudes, or disperses pattern. This study shown that MS at the stylomastoid foramen can not be used for the evaluation of the facial nerve conduction study in place of electrical stimulation(ES). As the transcranial MS can stimulate intracranial proximal portion of facial nerve directly and noninvasively, it can give additional information on the evaluation of facial nerve. Transcranial MS combined with ES may provide the means for assessing the entire facial nerve.