Mitsuru Iwai

Waveform changes in antidromic facial nerve responses in patients with Bell's palsy.

We repeatedly tested the antidromic facial nerve response within 7 days after onset of paralysis in patients with Bells palsy. None of 109 patients showed the triphasic waveform that reflects normal conduction of the facial nerve action potential. The waves recorded from patients showed biphasic, monophasic, or flat waveforms. Eighty-two of 88 patients with complete recovery showed biphasic waves, whereas half of the patients with nerve degeneration had monophasic or flat waves. Most patients with complete recovery maintained biphasic waves, but in patients with incomplete recovery, the waveforms changed to monophasic or flat, except in 1 case. The presence of monophasic or flat waves with a low facial score strongly suggests nerve degeneration. The antidromic facial nerve response is recommended as a method of diagnosing paralysis and monitoring the progression of intratemporal facial nerve damage during its early stages.

Initial Lesions in Bell’s Palsy and Ramsay-Hunt Syndrome

Conclusion: The antidromic facial nerve response (AFNR) revealed that the initial lesion in both Bell’s palsy and Hunt syndrome was mainly located around the geniculate ganglion within 1 week after onset of paralysis. The preoperative AFNR reflected the response near the initial lesion. Objectives: To review the initial lesion in Bell’s palsy and Ramsay-Hunt syndrome using intraoperative monitoring of the AFNR. Methods: 15 patients, including 8 with Bell’s palsy and 7 with Ramsay-Hunt syndrome, were checked for the AFNR before and during transmastoid decompression surgery within 1 week after onset of paralysis. The AFNR monitoring was performed at the posterosuperior part of the anulus tympanicus preoperatively and at 4 points of the facial nerve during surgery. The nerve conduction block sites were diagnosed by the AFNR waveform. Results: The monophasic wave revealing the block site was mainly observed at the geniculate ganglion in both diseases. The latencies of the preoperative responses corresponded to those recorded intraoperatively around the pyramidal segment of the facial nerve.

Early Assessment of Nerve Degeneration Using the Antidromic Facial Nerve Response

Conclusion: The antidromic facial nerve response (AFNR) is recommended as a monitoring method to detect cases resulting in facial nerve degeneration within 1 week after onset in patients with Bell’s palsy and Hunt syndrome. Objectives: The purpose of this study was to establish criteria for the AFNR to predict the prognosis of Bell’s palsy and Hunt syndrome in the early stages, not exceeding 1 week after onset. Materials and Methods: 54 patients, including 40 with Bell’s palsy and 14 with Hunt syndrome, were examined in this study. All patients were tested for the AFNR within 1 week after onset of paralysis and AFNR waveforms were analyzed. Four AFNR parameters, the total (peak-to-peak) amplitude (T-amp), the amplitudes of the positive wave (P-amp) and the negative wave (N-amp), and the N-amp/T-amp (N/T) ratio, were compared with the outcomes of facial paralysis. Results:In most patients with poor outcomes, T-amp was <4 µV and N-amp was <2 µV. The mean value of the N/T ratio in patients with a poor outcome fell to <0.4 after the 3rd day from onset, while that in patients with a good outcome was stable between 0.4 and 0.6 during the first week.

Computer Simulation of Antidromic Facial Nerve Response Waveform

Conclusion: An assessment of facial nerve (FN) damage on the basis of antidromic facial nerve response (AFNR) was established by computer simulation analysis. Computer simulation has the advantage of being able to assume any type of lesion. In the near future, computer analysis should provide another experimental method which displaces animal experiments, thus circumventing the ethical dilemma associated with animal experiments. Background: AFNR is a promising method to monitor intratemporal FN lesions. Clinical application of AFNR showed that waveform changes reflected the site and degree of the lesion. However, the association between the waveform changes and pathologic conditions of FN remains to be clarified. Objective: To analyze the association between waveform changes and the degree and site of nerve degeneration or blockade with the use of computer simulation, and to speculate the degree and involvement of the intratemporal FN lesions underlying the changes of AFNR waveforms. Methods: AFNR waveform, latency and amplitude changes in various types of nerve conduction block in the intratemporal FN were analyzed with the use of a computer simulation program based on the solid-angle approximation theory. Result: The present computer simulation revealed a temporal increase in the peak-to-peak amplitude between 1st and 2ndwaves, when the nerve blockade extends 1 mm distally from the recording site. Generally, AFNR in severe palsy cases gradually decreases in amplitude as the waveform change from biphasic to monophasic, ultimately falling into non-response. According to the computer simulation, the decay of AFNR reflects conduction blocking in 63% or more of FN fibers. The amplitude ratio of the first positive/negative wave was indicative of the site of the lesion in relation to the recording site. The ratios were <0.586 when the lesions were situated >1 mm proximal and they were >0.667 when the lesions were peripheral to the recording site.

Clinical Application of Antidromic Facial Nerve Response. Studies in Normal Subjects.

We recorded antidromic facial nerve responses (AFNRs) in 64 normal ears of 51 subjects who had unilateral and bilateral normal function of the facial nerves to develop criteria for clinical application. The facial nerve was stimulated with a catheter electrode inserted into the parotid duct, and AFNR was recorded with a needle electrode placed mainly at the tympanic annulus immediately posterior to the short process. Stimulus thresholds, latencies and amplitudes were determined. AFNRs were recorded successfully in 58 ears (90.6%). The reasons for unsuccessful recording were failure of insertion of the catheter electrode (3 cases), mistakes of recording (2) and pain (1). The mean stimulus threshold, latency and amplitude was 1.3mA, 2.15ms and 15.5 μV, respectively. Amplitudes of AFNRs varied in each subject. Each parameter was also different on the right and left sides, but differences between serial tests on one side were comparatively small. The authors conclude that AFNR is a very useful method for monitoring facial nerve damage in the temporal bone and that chronological changes of the response on the paralyzed side are the most reliable in the evaluation of facial nerve function.

Audible Pulsatile Tinnitus. A Report of Three Cases.

The purpose of this paper is to remind physicians of the necessity of performing auscultation and angiography in cases of pulsatile tinnitus. Tinnitus is a subjective sensation in the ear and is usually attributed to untreatable inner ear disorders. Pulsatile tinnitus, however, is usually treatable. We report here 3 cases of pulsatile tinnitus in patients with A-V shunts whose tinnitus was audible. Phonocardiograms showed that the murmurs were synchronous with cardiac systole. Angiographic examination revealed A-V shunts. The tinnitus was greatly reduced by occlusion of the responsible arteries with embolisation, coils, and irradiation. Conventional X-ray and MR images failed to reveal any anomalies in our 3 patients. We advise examination with auscultation and angiography in patients with pulsatile tinnitus.