Vol.95 No.10 contentsPRACTICA OTO-RHINO-LARYNGOLOGICA
Vol. 95 No. 10 October 2002
Electrical Diagnosis for Facial Palsy
Masaru Aoyagi
(Yamagata University)
Electrical examinations for the diagnosis of facial palsies are reviewed. Because the recovery of nerve function is prescribed by the degree of wallerian degeneration and the degenerated nerve fibers are not responsive to stimulation, the examinations using electrical stimulation are important for the accurate prognostic diagnosis of facial palsy.
Because of its simplicity and convenience, the nerve excitability test (NET) is the most popular in clinical use. But its reliability is insufficient. Electroneurography (ENoG) is more reliable either than NET or the maximal stimulation test. However, when a facial nerve is stimulated peripheral to the injury site, the prognosis cannot be estimated correctly until the degenerations are completed in the stimulus site. Thus, NET and ENoG are not significant within 7-10 days after the onset for prognostic diagnosis.
Using transcranial magnetic stimulation (TMS), the facial nerve can be stimulated around the fundus of the internal auditory meatus, which is central to the injury site in most facial palsies. Patients having a good prognosis can be identified using TMS in the early stage of palsy. Though the examination technique developed by Saito et al. (1992) is a bit complicated, antidromic facial nerve-evoked potential provides accurate information about nerve degeneration in the early stage of palsy.
For bilateral facial palsy, the measurement of facial nerve conduction velocity is useful for the prognostic diagnosis (Tojima, 1988). The measurement of the distribution of facial nerve conduction velocity using Hopf's collision method (Saito, 1991) contributed to the analysis of the pathophysiology of Bell's palsy, which is thought to be a compression neuropathy.
Blink reflex is useful in the prognostic diagnosis and also in the estimation of synkinesis as a sequela of palsy. F-waves caused by neuronal recurrent discharge due to antidromic impulse have recently been used in the estimation of recovery of damaged nerves.
Key words : electrical diagnosis, facial palsy, prognosis