The annual incidence of peripheral facial paralysis is 20 to 30 per 100,000 persons, among which Bell's palsy is the most common cause of the disease, constituting approximately 60% to 75% of the overall patients with acute facial nerve palsy [1]. The typical signs and symptoms of Bell's palsy include paresthesia of some parts of the ear and dysautonomia of the parotid gland, the gustatory sense in the anterior two-thirds of the tongue occurring through the chorda tympani nerve, and the lacrimal gland, as well as paralysis and attenuation of the muscles controlled by the facial nerve [2]. Ramsay Hunt syndrome, the keynote symptoms of which are facial nerve palsy, ear pain, and herpetic dermatomeric rash on the skull, is another common cause of facial paralysis. This disease is known to comprise about 12% of all patients with acute facial palsy [3]. Recent studies have reported that Bell's palsy and Ramsay Hunt syndrome result from herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV), respectively, each being reactivated after latent infection of the geniculate ganglion [4-7]. According to Fisch and Esslen's research [8], their examination of 3 patients with Bell's palsy revealed that nerve impulses were blocked at the proximal part of the geniculate ganglion and at the medial part of the internal acoustic canal when electrical stimulation was being performed on exposed facial nerve during middle cranial fossa decompression. Gantz et al. [9] also observed nerve conduction block at the proximal part of the geniculate ganglion on 69% of 16 patients suffering from Bell's palsy who showed denervation in 90% to 98% in the preoperative electroneuronography when in the same way electrical stimulation was performed on the facial nerve during operation. These studies together suggest that the initial lesions of Bell's palsy and of Ramsay Hunt syndrome may exist in upper part of the geniculate ganglion.

Early diagnosis is crucial to estimating a patient's prognosis for these 2 diseases because patients with Bell's palsy are expected to have a higher recovery rate than those with Ramsay Hunt syndrome, if the patient receives proper medical treatment [10]. Among a variety of electrical diagnosis/screening tests for such acute facial palsy, the facial nerve conduction test has been used for the prognosis of the disease. The recovery rate varies with the degree of denervation [11,12]. However, the validity of the electroneuronography falls short during the initial several days, before Wallerian degeneration of the facial nerve advances to the distal part of the stylomastoid foramen [13]. To overcome this drawback, studies have been carried out employing transcranial magnetic stimulation at the initial stage of the illness. The transcranial magnetic stimulation has the facial nerve of the internal acoustic canal depolarized through the magnetic field, giving rise to motor-evoked potential [14,15]. It has already been reported throughout previous literature that when transcranial magnetic stimulation was conducted on patients with Bell's palsy, the motor-evoked potential disappeared or decreased within several hours after the development of the symptoms [13,14]. Nowak et al. [16] confirmed that the motor-evoked potential decreased or disappeared in not only Bell's palsy, but also in Ramsay Hunt syndrome when transcranial magnetic stimulation was performed within 3 days after the development of the symptoms. Considering that the decrement of compound muscle action potential and the degree of facial palsy were more significant in Ramsay Hunt syndrome than in Bell's palsy, Nowak et al. [16] also suggested that more severe and faster axon damage may occur in facial palsy caused by VZV. However, there are few papers that have studied the differences between Bell's palsy and Ramsay Hunt syndrome comparing both the facial nerve conduction test and the transcranial magnetic stimulation test.

The present research has attempted to provide basic data for the diagnoses and prognoses of acute facial palsy patients after securing the neurophysiological differences between the 2 diseases, by comparing amplitude differences of compound muscle action potential in the facial nerve conduction test and the transcranial magnetic stimulation test on the healthy side (normal people) and on the affected side (patients with either Bell's palsy or Ramsay Hunt syndrome to whom the symptoms of facial nerve paralysis just emerged within several days) of a patient's face.

Anatomically, the facial nerve constitutes 80% of the labyrinthine segment. Any inflammation or edema of this area in acute facial palsy patients is thought to lead to swelling of the facial nerve, which may develop a temporary block of nerve conduction or axonotmesis causing Wallerian degeneration. Conduction block or axonotmesis in Bell's palsy patients, as takes place in the medial temporal bone, the upper part of stylomastoid foramen at which electrical stimulation is to be conducted at facial nerve conduction test, is hard to confirm within 3 days immediately after symptom onset [18-21]. Also, the diagnosis of Ramsay Hunt syndrome at the first stage is difficult to make through facial nerve conduction test because the disease has its initial lesion at the geniculate ganglion as same as does Bell's palsy [6,22]. For Bell's palsy patients, on the other hand, motor-evoked potentials generated by transcranial magnetic stimulation, different from those measured by facial nerve conduction testing, remarkably decreased or disappeared in a few hours immediately after the development of the symptoms [13,14]. Also by transcranial magnetic stimulation test, conduction block or axonotmesis of the facial nerve for Ramsay Hunt syndrome patients can be detected in its initial phase, because these tests show pathophysiological and electrodiagnostic signs similar to those of Bell's palsy [16].

Nowak et al. [16], who performed research on 70 patients with facial palsy whose symptoms were detected within 3 days after symptom onset, maintained that the lower rate of compound muscle action potentials on facial nerve conduction testing was more significant in the Ramsay Hunt syndrome patients than in the Bell's palsy patients; these findings seemed to be responsible for more rapid and serious axonal damage in Ramsay Hunt syndrome patients than in Bell's palsy patients. Peitersen's research [23] confirmed a more unfavorable prognosis with Ramsay Hunt syndrome patients than for Bell's palsy patients. The present case showed that there was no statistical significance in the nerve block rates of facial nerve conduction test between the 2 groups; however, the nerve block rate increased considerably in the Ramsay Hunt syndrome cases, while there was no statistically significant difference found between the 2 groups in the nerve block rates on transcranial magnetic stimulation testing. However, the differences between the nerve block rates of the 2 tests, that is, the values earned by subtracting the nerve block rate of facial nerve conduction test from that of transcranial magnetic stimulation test, decreased significantly, which suggested that axonal injury progressed more rapidly in the Ramsay Hunt syndrome patients than in the Bell's palsy patients.

There has been a research result that long-term recovery rate of Bell's palsy patients was found unsatisfactory when its initial phase involved serious facial paralysis or when the denervation rate on facial nerve conduction test performed after its incidence reached more than 90% [24]. In addition, if we distinguish incomplete paralysis from complete paralysis based on the clinical standards, 94% of incomplete palsy patients and 61% of complete palsy patients recovered full function in the case of Bell's palsy, whereas for Ramsay Hunt syndrome only 66% of incomplete palsy patients and 10% of complete palsy patients were restored to full function, both altogether showing synkinesis [23,25]. Nowak et al. [16] argued that the degrees of facial paralysis and the decrement in the amplitudes on facial nerve conduction test measured within 3 days right after the onset of the palsy were correlated quantitatively to each other in patients with Bell's palsy (r²=0.70) and those with Ramsay Hunt syndrome (r²=0.66). In the present case, we tried to determine the relevance of H-B FGS to the nerve block rates on transcranial magnetic stimulation testing and on facial nerve conduction testing performed within 7 days of symptoms onset, but failed to find any statistically significant correlation. Comparing the present patient subjects with those in the previous studies, we suspect this was caused by the fact that the differences in the degrees of facial paralysis in our case were not diverse enough.

However, the nerve block rates on facial nerve conduction testing and transcranial magnetic stimulation testing showed a strong correlation to one another in both groups. Then, it is thought that performing a transcranial magnetic stimulation test within the first few days after symptom onset should be beneficiary towards making a prognosis for patients. On the contrary, a transcranial magnetic stimulation test 3 days or more after symptom onset may depreciate the diagnostic accuracy because of the progression of axonotmesis [20]. Because comparing the results of transcranial magnetic stimulation testing and facial nerve conduction testing helps in the diagnosis and prognosis of Bell's palsy and Ramsay Hunt syndrome, performing transcranial magnetic stimulation testing along with facial nerve conduction testing, to determine the progress rate and degree of lesions are expected to be useful towards making diagnoses and early prognostic predictions.

In conclusion, the present study has shown that for Ramsay Hunt syndrome and Bell's palsy transcranial magnetic stimulation test performed within the first few days after the onset of facial palsy has a high diagnostic value, correlated significantly with facial nerve conduction test. By comparing the results from transcranial magnetic stimulation testing and facial nerve conduction testing, we confirmed that axonotmesis injuries progress more rapidly in patients with Ramsay Hunt syndrome than in patients with Bell's palsy. These results seem to be beneficiary enough to help make the differential diagnosis of Bell's palsy and Ramsay Hunt syndrome, contributing to the ability to make prognostic predictions and treatment plans for patients. In the case of performing electrophysiologic testing to assess the facial nerve activity of patients with acute facial palsy, it is recommended to conduct facial nerve conduction tests along with transcranial magnetic stimulation tests for additional information about the neurophysiological status of a patient's facial nerve. By carrying out follow-up checks on patients with facial palsy, it is henceforth necessary to perform further studies in order to confirm how much the transcranial magnetic stimulation test could be useful in making prognostic predictions.