Evoked electromyography and idiopathic facial paralysis

An electrophysiological prognostic diagnosis for facial palsy

Two electrophysiological tests for facial palsy-electroneurography (ENoG) and nerve excitability test (NET)-were reviewed. ENoG has advantages over NET in that it reflects the percentage of degenerated facial nerve fibers and can provide an accurate prognosis. However, as disadvantages, ENoG requires large, expensive equipment, and such supramaximal electrical stimulation can be quite painful for patients. NET is less painful due to weak stimulation with just enough current to meet the threshold, and the required equipment is compact and inexpensive to procure. However, it is impossible to calculate the percentage of degenerated nerve fibers, and NET is inferior to ENoG in terms of accurate prognostic prediction for facial palsy. The appropriate timing for both ENoG and NET is 7 to 10 days after the onset. While ENoG has proven more popular than NET because of its accuracy for prognostic prediction, we should not predict the prognosis of facial palsy based solely on the results of electrophyisiolgical examinations; a comprehensive evaluation including the facial muscle grading system is essential.

Is There Any Relation between Serum Levels of Interleukin-10 and Neurophysiological Abnormalities in Bell's Palsy?

Background

Bell's palsy is the most common cause of peripheral facial palsy. The etiology and treatment of Bell's palsy are still controversial. Previous studies emphasize the role of herpes simplex and herpes zoster viruses in this ailment. The role of Interleukin-10 (IL-10) in Bell's palsy is yet unknown, and few studies have shed light on the matter. This study intended to assess the prognostic value of IL-10 and its relation to the intensity of electrodiagnostic abnormalities and evaluate its potential use as a factor for judging the need for medical or surgical interventions.

Materials and Methods

30 patients in the acute phase of Bell's palsy participated in this study. Peripheral blood samples were obtained for IL-10 assessment within the first 72 hours (before commencing treatment), and a nerve conduction study (NCS) was performed six days after symptom onset.

Results

There was no significant correlation between IL-10 serum levels and the severity of nerve conduction pathology in Orbicularis oculi and Orbicularis oris muscles. Also, IL-10 serum levels did not show any meaningful relationships with participants' age, gender, or symptoms.

Conclusion

The IL-10 serum levels are not relevant to the pathology of Bell's palsy, and the assessment of IL-10 serum levels cannot be used as an alternative to NCS for evaluating the severity of acute Bell's palsy.

Diagnostic Value of Facial Nerve Antidromic Evoked Potential in Patients With Bell's Palsy: A Preliminary Study

Objective

To assess the practical diagnostic value of facial nerve antidromic evoked potential (FNAEP), we compared it with the diagnostic value of the electroneurography (ENoG) test in Bell's palsy.

Methods

In total, 20 patients with unilateral Bell's palsy were recruited. Between the 1st and 17th days after the onset of facial palsy, FNAEP and ENoG tests were conducted. The degeneration ratio and FNAEP latency difference between the affected and unaffected sides were calculated in all subjects.

Results

In all patients, FNAEP showed prolonged latencies on the affected side versus the unaffected side. The difference was statistically significant. In contrast, there was no significant difference between sides in the normal control group. In 8 of 20 patients, ENoG revealed a degeneration ratio less than 50%, but FNAEP show a difference of more than 0.295±0.599 ms, the average value of normal control group. This shows FNAEP could be a more sensitive test for Bell's palsy diagnosis than ENoG. In particular, in 10 patients tested within 7 days after onset, an abnormal ENoG finding was noted in only four of them, but FNAEP showed a significant latency difference in all patients at this early stage. Thus, FANEP was more sensitive in detecting facial nerve injury than the ENoG test (p=0.031).

Conclusion

FNAEP has some clinical value in the diagnosis of facial nerve degeneration. It is important that FNAEP be considered in patients with facial palsy at an early stage and integrated with other relevant tests.

Electrodiagnostic studies in the management and prognosis of neuromuscular disorders

Prognosis remains a neglected aspect of modern medical care and research, behind diagnosis and treatment. The very term "electrodiagnosis" implies as much. Despite this, much has been published regarding the use and benefit of electrodiagnostic techniques in assessing prognosis and assisting in management of patients after the diagnosis has been established. This information is often hidden or otherwise not emphasized. This review summarizes the literature regarding the use of such techniques for prognosis and management of disorders of lower motor neurons, peripheral nerves, neuromuscular transmission, and muscle.

Pathophysiology of facial nerve paralysis induced by herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) has been proven to be a cause of Bell's palsy; however, the underlying pathophysiology of the facial nerve paralysis is not fully understood. We established a mouse model with facial nerve paralysis induced by HSV-1 infection simulating Bell's palsy and investigated the pathophysiology of the facial nerve paralysis. The time course of the R1 latency in the blink reflex tests paralleled the recovery of the facial nerve paralysis well, whereas electroneurographic recovery tended to be delayed, compared to that of the paralysis; these responses are usually seen in Bell's palsy. On histopathologic analysis, intact, demyelinated, and degenerated nerves were intermingled in the facial nerve in the model. The similarity of the time course of facial nerve paralysis and the electrophysiological results in Bell's palsy and the model strongly suggest that the pathophysiological basis of Bell's palsy is a mixed lesion of various nerve injuries.

Inhibition of Motor Nerve Regeneration in a Rabbit Facial Nerve Model

OBJECTIVES/HYPOTHESIS

We hypothesized that intramuscular injection of vincristine into the upper lip selectively prevents reinnervation of the target muscle (quadratus labii superioris) after facial nerve transection.

STUDY DESIGN

Prospective controlled experiment.

METHODS

Transection injuries with primary neurorrhaphy were performed just proximal to the buccal and zygomatic branches of both facial nerves in 20 rabbits. The left (experimental) quadratus labii superioris muscle was injected with 200 microg vincristine 72 hours after injury; the right (control) side was injected with saline. Functional, electrophysiological and histological studies were performed 6 weeks after surgery.

RESULTS

After 6 weeks, the control side had a mean axon count (distal buccal branch) of 1160, conduction velocity of 50.4 m/s, reduction of compound action potential amplitude of 44%, and functional index of 1.67 units. The experimental side had a mean axon count of 265, conduction velocity of 16.5 m/s, reduction of compound action potential amplitude of 88%, and a functional index of 0.176 units. All parameters were significantly reduced by vincristine blockade (P <.05). The zygomatic division (not exposed to vincristine) displayed a trend toward increased axon counts, but this was not statistically significant (P =.131).

CONCLUSIONS

These results demonstrate that reinnervation of a selected muscle can be prevented by injection of vincristine. Enhanced reinnervation of adjacent muscle groups may also occur. Thus, nerve blockade by vincristine may be useful for the prevention of synkinesis.

Prognostic value of electromyography in acute peripheral facial nerve palsy

OBJECTIVE

To analyze the value of electromyography in predicting recovery from acute idiopathic facial nerve paralysis.

STUDY DESIGN

Retrospective case-series review.

SETTING

University-based hospital department of otorhinolaryngology/head neck surgery.

PATIENTS

Three hundred fifty-five patients with sudden facial paralysis of unknown cause (Bell's palsy).

INTERVENTION

Treatment consisted uniformly of high-dose prednisolone, dextran, and pentoxifylline. Prognostication was based on electromyography performed not earlier than 10 to 14 days after the onset of palsy. The findings were classified according to Seddon into neurapraxia and axonotmesis/ neurotmesis. There is an inherent statement on prognosis in this classification because neurapraxia is presumed to recover completely within 8 to 12 weeks, whereas axonotmesis is most likely to be followed by sequelae.

MAIN OUTCOME MEASURES

Facial nerve function after 6 months.

RESULTS

Complete recovery was predicted correctly in 92.4% of cases. For the relatively rare and therefore principally more difficult predictable event defective recovery prognosis was still accurate in 80.8%.

CONCLUSION

The detection of spontaneous fibrillation in needle electromyography is a reliable sign predicting unfavorable outcome. An accuracy of 80.8% for predicting unfavorable outcome may be sufficient to advise patients what to expect in the course of their facial nerve disorder. However, it seems dubious to build a decision about surgical intervention on such a test, because in the process, unnecessary surgery would be accepted for as much as one fifth of the patient population.

Assessment of real-time clinical facial function during vestibular schwannoma resection

OBJECTIVES

To describe a technique for quantifying residual facial function after vestibular schwannoma surgery. The intraoperative electrophysiological results are correlated with immediate postoperative clinical facial function to assess technique validity.

STUDY DESIGN

Prospective blinded study.

METHODS

Thirty-two patients undergoing translabyrinthine resection of vestibular schwannoma were included. Compound muscle action potential (CMAP) amplitude was calculated to supramaximal stimulation of the facial nerve, proximal to vestibular schwannoma compression, at the brain stem. The procedure was repeated after tumor removal. Comparison of the two CMAP amplitudes enabled estimation of change in facial function during surgery. The data were correlated with intracranial tumor diameter and immediate postoperative clinical facial function.

RESULTS

CMAP amplitude recorded after tumor resection correlated with immediate postoperative clinical facial function (0.879, P < .01). Correlation was improved when residual facial function was calculated (0.944, P < .01). In contrast, preoperative tumor size had relatively poor correlation with immediate postoperative facial function (0.688, P < .01).

CONCLUSIONS

Comparison of electrophysiological data before and after tumor removal reduces intersubject variability resulting from intersubject variation in facial muscle morphology. Residual facial function closely correlates with immediate postoperative clinical facial function, assessed using the House-Brackmann grading system. From the data presented, the technique can inform the surgeon of current clinical facial function at any point during the dissection process.

Surgical management of Bell's palsy

OBJECTIVES

Incomplete return of facial motor function and synkinesis continue to be long-term sequelae in some patients with Bell's palsy. The aim of this report is to describe a prospective study in which a well-defined surgical decompression of the facial nerve was performed in a population of patients with Bell's palsy who exhibit the electrophysiologic features associated with poor outcomes. In addition, management issues related to Bell's palsy including herpes simplex virus typel etiology, the natural history, electrodiagnostic testing, and efficacy of surgical strategies are reviewed.

STUDY DESIGN AND METHODS

A multicenter prospective clinical trial was designed utilizing electroneurography (ENOG) and voluntary electromyography (EMG) to identify patients with Bell's palsy who would most likely develop poor return of facial function, as suggested by Fisch and Esslen. Patients who displayed electrodiagnostic features of poor outcome, >90% degeneration on ENOG testing and no voluntary motor unit EMG potentials within 14 days of onset of total paralysis, were offered a surgical decompression of the facial nerve through a middle cranial fossa surgical exposure, including the tympanic segment, geniculate ganglion, labyrinthine segment, and meatal foramen. Control subjects were those who displayed similar electrodiagnostic features and time course.

RESULTS

Subjects who did not reach 90% degeneration on ENOG within 14 days of paralysis all returned to House-Brackmann grade I (n = 48) or II (n = 6) at 7 months after onset of the paralysis. Control subjects self-selecting not to undergo surgical decompression when >90% degeneration on ENOG and no motor unit potentials on EMG were identified had a 58% chance of developing a poor outcome at 7 months after onset of paralysis (House-Brackmann grade III or IV [n = 19]). A group with similar ENOG and EMG findings undergoing middle fossa facial nerve decompression exhibited House-Brackmann grade I (n = 14) or II (n = 17) in 91% of the cases. An exact permutation test confirmed that the surgical group had a significantly higher proportion of patients with a good outcome (House-Brackmann grade I or II) (P = .0002).

CONCLUSION

Electroneurography in combination with voluntary EMG successfully identified patients who will most likely return to normal from those who had a greater chance of long-term sequelae from Bell's palsy. Surgical decompression medial to the geniculate ganglion significantly improves the chances of normal or near-normal return of facial function in the group that has a high probability of a poor result. Surgical decompression must be performed within 2 weeks of onset of total paralysis for it to be effective.

Twenty-four-hour oscillations of facial electroneurography parameters and their relationship to body temperature

The purpose of the present study was to assess the temporal variation of the facial electroneurography (ENoG) parameters recorded from the nasolabial crease and to compare it to the temporal oscillations of oral and facial cutaneous temperatures. Twelve healthy individuals were examined at 4-hour intervals for 2 consecutive days. Twenty-four-hour rhythms of oral and facial cutaneous temperatures were found in all subjects (troughs on average at 4:20 and 4:00 AM, respectively). Significant 24-hour oscillations of ENoG amplitude were found in all subjects, which were positively correlated to the oscillations of oral and facial cutaneous temperatures (trough on average at 2:40 AM). The compound action potential (CAP) latency fluctuated during the day and was negatively correlated with local temperatures. However, these fluctuations and correlations did not reach statistical significance. We also found a significant reduction of ENoG amplitude in 5 patients with artificial cooling of the face near the facial nerve. Also, there was a small increase in CAP latency with facial cooling. Interpreting ENoG recordings in accordance with oral temperature and recording time of day reduce the intertest variation.

Electroneurography during facial nerve expansion

With the use of tissue-expansion techniques, it is possible to elongate the facial nerve without impairing its function. The rate of expansion is limited by ischemic events imposed by stretching of the nerve and by anatomic characteristics of the nerve segment. In this study, we used various electroneurography techniques to determine the first sign of facial dysfunction during expansion. The main objective of the study was to ascertain test-retest variability of electroneurography techniques. Facial nerves were expanded in 16 cats with the use of a tissue expander secured more deeply to the main trunk. We conducted electroneurography measurements with the use of surface electrodes, temporary needle electrodes, and permanently implanted electrodes. Technique-dependent variations encountered with the surface electrodes made this method unreliable. Using implanted electrodes, we noted gradual worsening of the compound-action potential amplitude with increasing expansion. During acute expansion, reduction in compound-action potential amplitude was correlated with clinically observed deterioration of facial-nerve function. In this study, electroneurography with implanted electrodes was found to be the most reliable predictor of the rate of successful facial nerve expansion.

House-Brackmann and Yanagihara grading scores in relation to electroneurographic results in the time course of Bell's palsy

The results of House Brackmann and Yanagihara grading were compared with electroneurographic (ENoG) data in 30 consecutive patients with Bell's palsy. The examinations were made on mean days 11, 36 and 99. Twenty-four patients had a favourable outcome (Yanagihara > or = 36 at three months). Based on our observations, 23 (96%) of these could have been predicted by ENoG, 18 (75%) by Yanagihara grading and 6 (25%) by House Brackmann grading. Initially, the relative House Brackmann scores showed a slightly milder palsy than the Yanagihara scores, but in the follow-up period the gradings were almost identical. The mild palsies, defined on the initial ENoG results, initially demonstrated relatively less nerve dysfunction on ENoG than the clinical grading; by the first follow-up, the ENoG and clinical grading had both returned to normal. The intermediate palsies had almost the same initial relative clinical and ENoG values, but at the first follow-up (mean day 36), the facial function had returned to normal despite abnormally reduced, but improved, ENoG values. In the severely affected patients, the follow-up studies showed an improved clinical function but ENoG values still demonstrated a high degree of degeneration (slightly improved at second follow-up). In this study, patients with a favourable outcome were best predicted with ENoG. Clinical identification of these patients was more accurate with Yanagihara than with House Brackmann. Furthermore, in all three groups a clinical improvement, due to the release of neurapraxia, was noted at the first follow-up. The slow ENoG improvement noted at follow-up was probably due to nerve regeneration by collateral sprouting. Based on the time course of our ENoG findings, it appears that patients with a high degree of degeneration at both the initial examination and first follow-up have a poorer prognosis.

Facial electroneurography in Bell's palsy. Variability in the early stage and comparison between interpretation methods

To determine the variability of the abnormalities found in the electroneurography (ENG) of the facial nerve in cases of Bell's palsy during the initial two week period was one of the objectives of the authors. A second one was to investigate the value of ENG as a tool to determine an early prognosis of recovery utilizing two different methods. In the first one the amplitude of the compound muscular action potential (CMAP) obtained on the paralyzed side was compared to this potential on the opposite (normal) side. The second method compared the CMAP on the paralyzed side to normal standardized data from normal individuals. A group of 33 patients with Bell's palsy was followed until total recovery of for at least 4 months, if the recovery was not achieved earlier. It was observed that amplitude of the CMAP become stable towards the sixth day of palsy and this is a good time to establish the prognosis. Another conclusion is that both methods were equivalent to determine the prognosis in Bell's palsy.

Facial nerve electroneurography. Variability in normal subjects

Twenty normal individuals were submitted to facial nerve electroneurography using different techniques in order to determine the most accurate to obtain the latencies and amplitudes of the compound muscle action potentials (CMAP) of the facial muscles. First of all it was determined in which muscle or muscle group highest amplitude CMAP could be recorded with the lowest variability between sides and in test-retest. Different techniques were studied in order to determine which could give the best results. This was shown to be an arrangement of bipolar surface electrodes fixed to a plastic bar. The records with higher amplitude where obtained from the nasolabial fold muscles. Therefore 65 normal volunteers were examined using this technique and recording the potentials obtained over the nasolabial fold muscles. Normal values were determined (latency lower than 4.5 ms and amplitude larger than 2 mV--95% confidence limits).

Histologic correlation of the degenerating facial nerve with electroneurography

The myogenic compound action potential (CAP) measured by electroneurography (EnoG) is hypothesized to correlate directly with the number of viable motoneurons in the facial nerve. In an animal model (cat), two independent ENoG techniques, standardized recording lead placement (SRLP) and optimized recording lead placement (ORLP), were used to record CAPs evoked from nerves undergoing degeneration. Normal test-retest variability simulated human studies. Peripheral counts of viable axons correlated with N1 amplitude (ORLP ENoG), peak-to-peak (absolute) amplitude (both ENoG techniques), and area under the negative phase of the diphasic CAP waveform (both ENoG techniques) recorded over the whisker pad. These results validate ENoG as a reliable indicator of neural integrity following traumatic lesions of the facial nerve.

[Electroneurography of the facial nerve: methods of stimulation and records]

In this study it is, intended to establish the more appropriate points to register the compound action potential from m. frontalis m. orbicularis oculi and nasolabial fold muscles. The optimum site for stimulating electrodes and differences between the first and the last compound action potentials after 20 consecutive stimuli delivered at 1 Hz were analysed.

A model of waveform reliability in facial nerve electroneurography

This study identifies four factors that should be considered when evaluating the reliability of new testing methods in facial nerve electroneurography (ENOG): (1) waveform peak-to-peak amplitude; (2) response variability; (3) statistical significance of day-to-day test/retest differences; and (4) waveform morphology. These factors were applied to data gathered on seven normal subjects who had three trials of facial-nerve ENOG on three separate test days in order to determine an optimal recording electrode montage. Both bipolar and monopolar recording-electrode montages were used on the nasal alae and on the nasolabial crease. Resultant peak-to-peak amplitudes of combined motor action potentials were recorded and measured using a clinical evoked-potential instrument. A biphasic waveform shape with optimal peak-to-peak point rather than the nasolabial crease. The contribution to the assessment of response reliability of each of the four factors is discussed.

Facial nerve electroneurography with implanted electrodes. Experimental study in the rabbit

Facial nerve function was evaluated with permanently implanted electrodes for registration of electroneurography in an experimental model. The test-retest reproducibility was analyzed under normal conditions, as well as after facial nerve section. The mean observed intraindividual variation obtained at different sessions was 4%. We believe that the method is well suited for studies of experimental facial palsy.

Facial electroneurography: clinical and experimental investigations

Facial electroneurography (ENoG) appears to be a reliable prognostic test for intratemporal facial nerve paralysis. ENoG is objective and allows a permanent record to be maintained. Nonetheless, occasional inconsistencies in clinical correlation may diminish the utility of ENoG. A qualitative study was undertaken to identify the possible reasons for the inaccuracy of ENoG in some patients. Four clinical groups and one experimental group were studied: (1) normal subjects, (2) patients with acute facial palsy, (3) patients with progressive facial palsy, (4) patients with temporal bone tumors and normal facial function, and (5) animals in which one facial nerve was crushed and repaired. The reliability of ENoG is dependent on careful interpretation of data obtained by optimal electrode placement and stimulus duration.