Vol.96 No.4 contentsPRACTICA OTO-RHINO-LARYNGOLOGICA
Vol. 96 No. 4 April 2003
A
Study of the Distribution of Facial Nerve Conduction
Velocities by Transcranial Magnetic
Stimulation
Akira Arai, Akiko Hagiwara, Hiroshi Yoshikawa and Ginichiro Ichikawa
(Juntendo University)
Takuya Yamakawa
(Yamakawa Ear, Nose, Throat Clinic)
Objective: The purpose of this study was to evaluate by the collision method the distribution of nerve conduction velocities (DNCVs) of the facial nerve under transcranial magnetic stimulation (TMS), to better understand its neurophysiological characteristics.
Materials and Methods: The subjects were 13 normal volunteers and 3 patients with Bell's palsy. The experiments were carried out using Magstim model 200, a large coil measuring 90 mm in diameter with a maximal output of 2.0 tesla (T), and a Neuropack 8 (Nihon Kohden, Japan) to control the stimulation and record the electromyographical findings. The labyrinthine segment of the facial nerve within the temporal bone was selected as the site for transcranial magnetic stimulation, and the main trunk of the facial nerve that runs subcutaneously in the parotid region was selected as the site for electric stimulation. The reference electrode of the bipolar lead was placed over the mentalis muscle. The amplitude of compound muscle action potentials (CMAP) to the mentalis muscle was studied by the collision method.
Measurement and Results: The peak of DNCV was detected at 22 to 24 m/sec in 13 normal volunteers. The data showed a decrease in the number of thicker fibers, which tended to show faster conduction velocities, in Bell's palsy patients.
Conclusions: We were able to investigate the DNCVs of the facial nerve by TMS. Thicker myelinated fibers may be more susceptible to compression damage. From this finding it can be said that the compression of the nerve results in a state comparable with Bell's palsy.
Key words : transcranial magnetic stimulation (TMS), collision method, facial nerve, Bell's palsy