Electroneurography (ENoG), an objective electrophysiologic measurement of compound muscle action potentials (CMAPs), is used to assess the integrity of a peripheral motor nerve. This method has been used for many years. In our study using an electrophysiologic instrument (Medelec MS6), the stimulating electrode was placed over the facial nerve anterior to the tip of the mastoid process and was manipulated to obtain the maximum CMAPs amplitude from the frontal muscle. With 30 normal subjects and 20 patients with facial nerve palsy, the results showed that the latencies and amplitudes were different between the two groups. Motor evoked potential (MEP) is a new method. Ipsilateral facial muscles are excited by magnetic stimulation over the scalp when the coil is placed over the parieto-occipital region. Using a magnetic stimulator and EMG instrument (1500C4 DISA), CMAPs from the orbicularis oris and frontal muscle were measured. In 30 normal subjects, the CMAPs were similar in form but of longer latency than those obtained with electrical stimulation (ENoG). In 20 patients with lateral facial nerve palsy due to Bell's palsy, Hunt's syndrome or trauma, the latencies on the lesion sides were apparently longer and the amplitudes much lower than in the normals. Our studies suggest that magnetic stimulation will detect facial nerves in the region inside the temporal bone where they cannot be touched by electrical stimulation from in front of mastoid process. The use of both ENoG and MEP methods together allows for accurate measurement of proximal facial nerve conduction and also provides some quantitative measurement: thus, we can detect conduction block or axonal degeneration early.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent Adult