Transcranial magnetic stimulation in Bell's palsy

In Bell palsy, the site of lesion is located within the petrosal bone. Conventional electrophysiologic study of facial nerves consists of electrical stimulation around the stylomastoid foramen, and records the CMAP in muscles innervated by facial nerves. It is not possible to survey the lesion site in the acute stage, and patients should receive the examination in about two weeks after the onset of facial palsy when Wallerian degeneration occurs. Transcranial magnetic stimulation could elicit intracranial facial nerve action potential, which is considered to be across or just from the lesion site of Bell palsy. Therefore, we use the magnetic stimulation technique combined with electrical stimulation to survey 14 patients with acute Bell palsy. In all the cases, either in the acute stage or recovery stage, the transcranial magnetic stimulation fails to elicit CMAPs of facial nerves in the affected sides. This study suggests that the trans cranial magnetic stimulation of facial nerves is more sensitive than the conventional method in the acute stage of Bell palsy, however, it is not a valuable tool to predict the prognosis of this disease. Besides, it is also proposed that the lesion site of Bell palsy might be located at the site a little distal to the internal auditory meatus, which is considered to be the excitation site of transcranial magnetic stimulation of facial nerves.