Perioperative lesions of the facial nerve: follow-up investigations using transcranial magnetic stimulation

Peripheral facial palsy can occur after aural surgery and neurosurgery. Routine neurophysiological investigation (utilizing electrical stimulation and the blink reflex) does not allow the direct assessment of the site of a lesion. In the present study transcranial magnetic stimulation (TMS) was applied in order to evaluate the usefulness of this method for prognosis. Twenty-three patients with postoperative facial pareses (after removals of an acoustic neuroma in 12 patients and parotid tumors in 11) were investigated. Ipsilateral short-latency and contralateral long-latency responses (after cortex stimulation) were elicited. At the first examination (11.7 ± 9 days after onset of the palsy) the components of the blink reflex were absent in all cases. Responses to electrical stimulation were abnormal in 80%. Ipsilateral short-latency responses after TMS could be obtained in 7 patients. Pathological long-latency TMS responses were elicited in 17 patients. Follow-up investigations up to 2 years revealed no prognostic aspects from peripheral electrical stimulation, the blink reflex and the short-latency TMS response. The absence or extent of delay in long-latency responses at first examination was strongly correlated with final clinical outcomes. As improvements of the responses preceded clinical regressions of the paresis, TMS proved to be an important neurophysiological method for an early prognosis of recovery after perioperative lesions of the facial nerve.     

A clinical study on the magnetic stimulation of the facial nerve

OBJECTIVES: A clinical study on the usefulness of magnetic stimulation of the facial nerve, with special attention paid to the selection of the coil shape and stimulation procedures. STUDY DESIGN: The subjects consisted of 55 patients with Bell's palsy, 1 patient with a cerebellopontine angle (CPA) tumor, 1 patient with multiple sclerosis (MS), and 30 normal subjects. Three types of coils were used in this study; a 90-mm large single coil, a 40-mm small single coil, and a 20-mm small double coil. METHODS: The compound muscle action potentials (CMAPs) and long latency response were evoked by transcranial magnetic stimulation (TMS) with a 90-mm large single coil. The 40-mm small single coil was used to test blink reflex by aiming it at the supraorbital nerve as the target site. The subcutaneous activation of the infra-auricular facial nerve was performed with the 20-mm double coil. RESULTS: The reproducible CMAP and long latency responses were obtained from normal subjects with TMS. However, responses were observed only in patients with relatively mild Bell's palsy. The magnetic stimulation-evoked responses reflected the brainstem function in the patients with a CPA tumor and MS. CONCLUSION: Although magnetic stimulation remains inferior to conventional electric stimulation in some sense and requires further study, this method is potentially useful because it can stimulate the facial nerve continuously from the cortex to the periphery and can effectively evoke responses reflecting the brainstem function.     

Transcranial magnetic stimulation in acute facial nerve injury

OBJECTIVE/HYPOTHESIS: Available electrodiagnostic tests that are used to evaluate facial nerve injury examine the nerve distal to the stylomastoid foramen; because most facial nerve injuries are within the temporal bone, the tests cannot evaluate the nerve at or across the injury site. The interpretation of these tests depends on the predictability (or unpredictability) of distal degenerative process. Transcranial magnetic stimulation may be able to stimulate the nerve proximal to the injury site. The hypothesis of the present study is that in cases of mild traumatic facial nerve injury where axonal integrity is maintained, proximal stimulation of the nerve using higher than normal stimulus intensities to "overcome" the block at the injury site result in recordable facial nerve activity. STUDY DESIGN: A prospective controlled animal study comparing response to transcranial magnetic stimulation of the facial nerve in the following groups: mild injury, severe injury/transection, and control. METHODS: We studied 44 facial nerves in 22 cats. Fifteen nerves were subjected to mild trauma. Five nerves were severely crushed, 2 nerves were completely transected, and 22 nerves were not traumatized. All nerves were examined with the transcranial magnetic stimulation system before the trauma, immediately after the trauma, and at 3, 8, and 12 weeks after trauma. RESULTS: All nerves in the mild and severe trauma groups showed complete clinical paralysis immediately after trauma. The nerves in the mild trauma group showed significant increase in threshold as well as significant increase in latency for recordable facial muscle response to transcranial magnetic stimulation. Thresholds and latencies decreased gradually within 3 to 12 weeks and returned almost to preinjury levels. This paralleled the return of clinical facial muscle movement. In the severe trauma/transection group, the nerves had no facial muscle response to transcranial magnetic stimulation after trauma. Neither facial muscle response to transcranial magnetic stimulation nor facial muscle movements recovered. CONCLUSIONS: In cats transcranial magnetic stimulation can assess the integrity of the facial nerve after trauma and predict its potential for regeneration. This technique can excite the nerve proximal to the injury site and may play a role in the clinical evaluation of the acute traumatic facial nerve paralysis. It can be used immediately after trauma, because it does not depend on wallerian degeneration to occur.     

Prediction of facial nerve function following acoustic neuroma resection using intraoperative facial nerve stimulation

Methods of monitoring the facial nerve during posterior fossa surgery continue to evolve. In an effort to predict acute and final facial nerve function following acoustic neuroma resection, the lowest current applied to the facial nerve at the brainstem necessary to elicit facial muscle response was measured using strain gauge and electromyographic facial nerve monitors. A retrospective analysis of 121 patients who had undergone acoustic neuroma surgery was performed. Sixty-five patients had intraoperative facial nerve monitoring and 44 had sufficient data for inclusion in this study. The acute and final facial nerve functions, according to the House-Brackmann classification, were assessed with regard to intraoperative stimulation-current thresholds. Nineteen of 20 patients who required 0.10 mA or less to elicit a facial muscle response had a House-Brackmann grade I facial nerve outcome. The upper limit of the 95% confidence interval of stimulation threshold for patients with a final grade I facial nerve function is 0.17 mA. All of the patients in this study, with stimulation thresholds ranging up to 0.84 mA, had a final grade III or better result. A poor outcome in our series, a final grade III facial nerve function, is best predicted by a poor acute result, specifically an acute grade VI_A facial nerve function. We suggest that it is possible to predict the facial nerve function based on intraoperative threshold testing.     

Electrical evaluation of the facial nerve in acoustic neuroma patients: preliminary comparison between transcranial magnetic coil stimulation and electroneurography.

Subclinical involvement of the facial nerve by acoustic neuromas may be identified preoperatively using conventional electroneurography (ENoG). The clinical application of extratemporal stimulation distal to the stylomastoid foramen is limited in these cases by the more proximal site of the lesion. Transcranial magnetic coil stimulation (MCS) is a noninvasive means by which the facial nerve is stimulated at the level of the motor cortex or the brain stem, before it enters the internal auditory canal. Topographically such an assessment may have more diagnostic relevance than other forms of electrical stimulation in acoustic neuroma patients. To test this theory the facial nerves of 20 patients with acoustic neuromas were stimulated using ENoG and MCS preoperatively and 1 week postoperatively. Stimulation parameters were comparable and included threshold and suprathreshold levels of stimulation while compound action potential amplitudes and early and late response latencies were monitored. Facial nerve function was assessed clinically using the Stennert grading system. All the patients had clinically normal facial nerve function preoperatively. Normative data suggested a close correlation between threshold and suprathreshold amplitudes generated by both ENoG and MCS. To the contrary, in the pathologic ears there was a higher incidence of stimulus response abnormality determined by MCS than by ENoG. A comparison of these data, tumor size, and postoperative results promotes further evaluation of MCS as a prognostic index in acoustic neuroma patients.     

Electric field navigated transcranial magnetic stimulation for chronic tinnitus: A pilot study

Objective: Repetitive transcranial magnetic stimulation (rTMS) has shown potential in reducing tinnitus symptoms. We evaluated effects of electric field (E-field) navigated rTMS targeted neuroanatomically according to tinnitus pitch. Design: In this open methodological pilot study, the patients received E-field navigated 1-Hz rTMS in daily treatment sessions to the left superior temporal gyrus, targeted according to tonotopic representation of their individual tinnitus pitch. Patients rated their tinnitus intensity and annoyance with a numeric rating scale (NRS) from 0 to 10 at the baseline and after each rTMS session. They also rated their global impression of change (scale ? 3 to + 3) after the treatment. Study sample: Thirteen patients (mean age 53 years; 10 men, 3 women) with chronic, intractable tinnitus. Results: The mean intensity was 7.1 (SD 1.8) at the baseline, decreasing to 4.5 (SD 2.2) after the rTMS (p < 0.0001). The mean annoyance 7.0 (SD 1.8) at the baseline decreased to 4.0 (SD 2.4) after the treatment (p < 0.0001). Intensity diminished at least 30% in 8/13 patients and annoyance in 9/13 patients. A total of 10/13 patients felt subjective benefit from the treatment. Conclusions: These preliminary observations suggest that E-field-rTMS may improve the current treatment options for intractable tinnitus.     

Repetitive transcranial magnetic stimulation for tinnitus: a pilot study

OBJECTIVES/HYPOTHESIS: Low-frequency repetitive transcranial magnetic stimulation (rTMS) has been shown to alleviate tinnitus perception, presumably by inhibiting cortical activity associated with tinnitus. We conducted a pilot study to assess effectiveness of neuronavigated rTMS and its effects on attentional deficits and cortical asymmetry in four patients with chronic tinnitus using objective and subjective measures and employing an optimization technique refined in our laboratory. STUDY DESIGN: Randomized, placebo-controlled (sham stimulation) crossover study. METHODS: Patients received 5 consecutive days of active, low-frequency rTMS or sham treatment (using a 45-degree coil-tilt method) before crossing over. Subjective tinnitus was assessed at baseline, after each treatment, and 4 weeks later. Positron emission tomography/computed tomography (PET/CT) scans were obtained at baseline and immediately after active treatment to examine change in cortical asymmetry. Attentional vigilance was assessed at baseline and after each treatment using a simple reaction time test. RESULTS: All patients had a response to active (but not sham) rTMS, as indicated by their best tinnitus ratings; however, tinnitus returned in all patients by 4 weeks after active treatment. All patients had reduced cortical activity visualized on PET immediately after active rTMS. Mean reaction time improved (P < .05) after active but not sham rTMS. CONCLUSIONS: rTMS is a promising treatment modality that can transiently diminish tinnitus in some individuals, but further trials are needed to determine the optimal techniques required to achieve a lasting response. It is unclear whether the improved reaction times were caused by tinnitus reduction or a general effect of rTMS. PET/CT scans immediately after treatment suggest that improvement may be related to reduction of cortical asymmetry associated with tinnitus.     

Repetitive transcranial magnetic stimulation for tinnitus: a case study

OBJECTIVES/HYPOTHESIS: Correlate subjective improvements in tinnitus severity with restoration of cortical symmetry and sustained attention after neuronavigated low-frequency, repetitive transcranial magnetic stimulation (rTMS). STUDY DESIGN: Case study. METHODS: Positron emission tomography and computed tomography imaging (PET-CT) guided rTMS was performed on a 43-year-old white male with more than a 30 year history of bilateral tinnitus. rTMS was administered to the area of increased cortical activation visualized on PET-CT at a rate of 1 Hz for 30 minutes (1,800 pulses/session) for each of 5 consecutive days, with optimization applied on day 5 using single pulses of TMS to temporarily alter tinnitus perception. Subjective tinnitus severity was rated before and after rTMS using the tinnitus severity index with analogue scale. Attention and vigilance were assessed before and after therapy using the psychomotor vigilance task (PVT), a simple reaction time test that is sensitive to thalamocortical contributions to sustained attention. Posttherapy PET-CT was used to evaluate any change in asymmetric cortical activation. RESULTS: The most marked reduction in tinnitus severity occurred after rTMS optimization; this persisted up to 4 weeks after rTMS. PVT testing showed the patient exhibited a statistically significant improvement in mean slowest 10% reaction times after rTMS (P = .004). PET-CT imaging 2 days after the cessation of rTMS showed no changes in cortical blood flow or metabolic asymmetries. CONCLUSIONS: Low-frequency rTMS applied to the primary auditory cortex can reduce tinnitus severity, with rTMS optimization yielding the most favorable results. Beneficial changes occurring in the patient's slowest reaction times suggest that attentional deficits associated with tinnitus may also respond to low-frequency rTMS.     

Electrophysiologic evaluation of the facial nerve in patients with acoustic neuromas. Preliminary results of a comparative study between conventional electroneurography and transcranial magnetic pulse stimulation]

Subclinical invasion of the facial nerve by acoustic neuromas may be identified preoperatively using conventional electroneurography (ENOG). The clinical application of extratemporal stimulation distal to the stylomastoid foramen is limited in these cases because of the more proximal site of the lesion. Transcranial magnetic coil stimulation (MCS) is a non-invasive means by which the facial nerve is stimulated at the level of the motor cortex or the brain stem before it enters the internal auditory canal. Topographically such an assessment may have more diagnostic relevance than other forms of electrical stimulation in acoustic neuroma patients. To test this theory the facial nerves of 20 patients with an acoustic neuroma were stimulated using ENOG and MCS before and 1 week after operation. Stimulation parameters were comparable and included threshold, double-threshold and supra-threshold levels of stimulation while compound action potential amplitudes and early and late response latencies were monitored. All the patients had clinically normal facial nerve function preoperatively. Using ENOG 65% of the patients showed amplitude reduction on the tumour side, whereas 70% of these patients had a reduction of amplitude to MCS. Combining both techniques, 88% of the patients had a significant amplitude reduction on the neuroma side. Comparison of the preoperative threshold measurements of both techniques showed that there was a significantly higher incidence of detection of lesions on the diseased side in neuromas larger than 2 cm by the use of MCS.     

Magnetic stimulation of the facial nerve

Electrical testing of the facial nerve has evolved into an important means of assessing neural injury. However, the inability to stimulate the intratemporal facial nerve electrically results in a delay in diagnosis, because axonal degeneration must progress distal to the stylomastoid foramen before testing can be meaningful. To circumvent this problem, we began an investigation of magnetic stimulation of the facial nerve, because pulsed magnetic fields can pass unattenuated through all body structures, including bone. Normal volunteers and one patient with acute facial paralysis were studied with both magnetic and electric stimulation of the facial nerve. The results indicate that (1) magnetic stimulation was more comfortable because high current levels were not required at the skin surface to assure indepth stimulation, (2) magnetic and electric stimulation of the extratemporal facial nerve resulted in nearly identical compound muscle action potentials, indicating that the sites and mechanisms of neural depolarization are similar, and (3) transtemporal magnetic stimulation appears to allow depolarization of the proximal intratemporal nerve. These preliminary results are encouraging and indicate that magnetic stimulation of the facial nerve warrants further investigation.     

Intracranial supramaximal facial nerve stimulation: A murine model

Purpose

Supramaximal facial nerve stimulation is an applied current sufficient to evoke a maximal electromyographic response of facial musculature. It is used during cerebellopontine angle surgery for prognostication of postoperative nerve function. We utilized a rat model to examine safe parameters for intracranial electrical stimulation.

Materials and methods

Intracranial facial nerve stimulation with electromyographic monitoring of 14 rats was performed. Supramaximal current level was determined and 50 additional pulses of supramaximal (4 rats), 3 times supramaximal (4), 10 times supramaximal (3), or zero (3) current were applied. To monitor progression of facial nerve injury, video recordings of vibrissae movements and eye closure were captured at 1, 3 and 28 days after surgery; animals were sacrificed on day 28, when nerve morphometry was performed.

Results

One rat in the supramaximal stimulation group (of 4), and one rat in the 10 times supramaximal stimulation group (of 3) demonstrated persistent impairment of facial nerve function as evidenced by decreased amplitude of vibrissae sweeping and eye closure impairment. The remainder of rats in all experimental groups demonstrated symmetric and normal facial nerve function at all time points.

Conclusions

A novel animal model for supramaximal stimulation of the rat intracranial facial nerve is described. A small proportion of animals demonstrated functional evidence of nerve injury postoperatively. Function was preserved in some animals after stimulation with current order of magnitude higher than supramaximal levels. Further study with this model is necessary to definitively isolate the effects of surgical trauma from those of supramaximal electrical stimulation.     

Magnetic stimulation of the facial nerve

Intracranial activation of the facial nerve is now possible with the noninvasive techniques of magnetic stimulation. Brief magnetic pulses generated by a coil overlying the parietal scalp elicit compound muscle action potentials of similar shape and amplitude and greater latency than those produced by electroneurography. Mapping studies demonstrate the compound muscle action potentials to be of constant latency and varying amplitude with changing coil location. Maximum compound muscle action potential amplitudes are obtained with the coil center located in a rectangular area superior and posterior to the ear canal. A comparison of large and small diameter coils showed them to be equally effective for painless facial nerve stimulation; however, the smaller coil allowed for a more localized field of activation. Magnetic stimulation has the potential to provide cross-the-lesion testing of facial nerve function.     

Repetitive transcranial magnetic stimulation and chronic tinnitus

CONCLUSION: There is a good theoretical basis and early research evidence suggesting that transcranial magnetic stimulation (TMS) may have treatment potential in tinnitus. Further studies with larger sample sizes and additional assessment of neurobiological effects are necessary. OBJECTIVES: Tinnitus is a common and often severely disabling disorder for which there is no satisfactory treatment. TMS is a new, non-invasive method of modifying the excitability of the cerebral cortex, which has proven effective in auditory hallucinations and other disorders. Some early studies have been published in which TMS has been used in the treatment of tinnitus. The objective of this paper is to examine the literature and consider the potential for TMS as a therapy in tinnitus. METHODS: A thorough search of the tinnitus and TMS literature was conducted, and all available relevant material was examined. RESULTS: Tinnitus is common, with a prevalence of 8.2% in subjects aged 50 years and over, and may be associated with great distress (tinnitus sufferers). There are no effective treatments. Tinnitus is frequently associated with deafness, and may be the result of a pathological plasticity process. Neuroimaging studies demonstrate increased activity within the central auditory system. TMS is a non-invasive method of modulating excitability in cerebral cortex. It uses electromagnetic principles and has been successfully employed in the treatment of other conditions associated with increased activity of the cerebral cortex. Meanwhile, a growing number of studies suggest that repetitive TMS may be effective in the treatment of chronic tinnitus.     

Short-term effects of repetitive transcranial magnetic stimulation on sleep bruxism-a pilot study

The purpose of this study was to investigate the effects of repetitive transcranial magnetic stimulation (rTMS) on patients with sleep bruxism (SB). Twelve patients with SB were included in an open, single-intervention pilot study. rTMS at 1 Hz and an intensity of 80% of the active motor threshold was applied to the ‘hot spot’ of the masseter muscle representation at the primary motor cortex bilaterally for 20 min per side each day for 5 consecutive days. The jaw-closing muscle electromyographic (EMG) activity during sleep was recorded with a portable EMG recorder at baseline, during rTMS treatment and at follow-up for 5 days. In addition, patients scored their jaw-closing muscle soreness on a 0–10 numerical rating scale (NRS). Data were analysed with analysis of variance. The intensity of the EMG activity was suppressed during and after rTMS compared to the baseline (P 5 0.04; P 5 0.02, respectively). The NRS score of soreness decreased significantly during and after rTMS compared with baseline (P,0.01). These findings indicated a significant inhibition of jaw-closing muscle activity during sleep along with a decrease of muscle soreness. This pilot study raises the possibility of therapeutic benefits from rTMS in patients with bruxism and calls for further and more controlled studies.     

Magnetic facial nerve stimulation in Bell's palsy.

The transcranial magnetic stimulation (TMS) technique makes it possible to stimulate the intracranial part of the facial nerve. In a total of 51 patients with acute Bell's palsy, TMS was performed, and the responses were compared with those elicited by conventional extracranial electric stimulation (EES). Clinical recovery was evaluated at 258-539, mean 410, days from the beginning of the palsy. With both techniques the motor evoked potentials (MEPs) could always be elicited on the healthy side, the mean latency being 4.7 ms with TMS and 3.7 ms with EES. In the acute phase, TMS elicited MEPs on the paralyzed side in 47% of the patients, and EES in 98%. The patients with TMS elicitable MEPs during the first 4 days of the palsy had significantly better recovery than those without response (p less than 0.05). The difference in recovery between patients with or without elicitable TMS responses on days 5-8 and 9-14 was not significant. In EES, the amplitude difference between the two sides within the first 4 days was not significantly (p greater than 0.05) different. On days 9-14 the patients with a less than 80% difference between the two sides recovered significantly (p less than 0.05) better than those with a difference of greater than or equal to 80%, So, TMS may be of help in the early prognosis of Bell's palsy.     

A quantitative study of nerve fibers in the human facial nerve

Summary The facial and intermediate nerves were quantitatively evaluated in seven patients who died from systemic malignancies not involving the facial nerve. In addition, five of the specimens were also qualitatively evaluated by measuring the total and axon diameters of the facial and intermediate nerve fibers. In two cases the facial nerve fibers were counted at five different levels. The total number of myelinated nerve fibers in the facial nerve varied from 7500 to 9370. The total number of myelinated nerve fibers in the intermediate nerve varied between 3120 and 5360. The peak diameter of the facial nerve axon was between 4 and 6 m, and was between 2 and 3 m in the intermediate nerve. When comparing nerve segments at different anatomical levels, the largest amount of nerve fibers was found at the level of the middle mastoid portion. However, this number did not reach the amount of nerve fibers counted in the internal acoustic meatus.Prof. H. Spoendlin died in November 1991 after a lengthy illness     

Electric field-navigated transcranial magnetic stimulation for chronic tinnitus: a randomized,placebo-controlled study

Objective: Repetitive transcranial magnetic stimulation (rTMS) may alleviate tinnitus. We evaluated effects of electric field (E-field) navigated rTMS targeted according to tinnitus pitch. No controlled studies have investigated anatomically accurate E-field-rTMS for tinnitus. Design: Effects of E-field-rTMS were evaluated in a prospective randomised placebo-controlled 6-month follow-up study on parallel groups. Patients received 10 sessions of 1?Hz rTMS or placebo targeted to the left auditory cortex corresponding to tonotopic representation of tinnitus pitch. Effects were evaluated immediately after treatment and at 1, 3 and 6 months. Primary outcome measures were visual analogue scores (VAS 0–100) for tinnitus intensity, annoyance and distress, and the Tinnitus Handicap Inventory (THI). Study sample: Thirty-nine patients (mean age 50.3 years). Results: The mean tinnitus intensity (F₃?=?15.7, p?F₃?=?8.8, p?=?0.0002), distress (F₃?=?9.1, p?=?0.0002) and THI scores (F₄?=?13.8, p?p?=?0.082 and p?=?0.065). Conclusions: Despite the significant effects of rTMS on tinnitus, differences between active and placebo groups remained non-significant, due to large placebo-effect and wide inter-individual variation.