Investigation of facial motor pathways by electrical and magnetic stimulation: sites and mechanisms of excitation.

A refined technique is described for non invasive examination of the facial motor pathways by stimulation of the extra- and intracranial segment of the facial nerve and the facial motor cortex. Surface recordings from the nasalis muscle rather than from the orbicularis oris muscle were used, since the compound muscle action potential (CMAP) from this muscle showed a more clearly defined onset. Electrical extracranial stimulation of the facial nerve at the stylomastoid fossa in 14 healthy subjects yielded a mean distal motor latency of 3.7 ms (SD 0.46), comparable with reported latencies to the orbicularis oris muscle. Using a magnetic stimulator, transcranial stimulation of the facial nerve was performed. The mechanism of transcranial magnetic facial nerve stimulation was studied using recordings on 12 patients who had facial nerve lesions at different locations, and with intraoperative direct measurements in four patients undergoing posterior fossa surgery. The actual site of stimulation could be localised to the proximal part of the facial canal, and a mean "transosseal conduction time" of 1.2 ms (SD 0.18) was calculated. The cerebrospinal fluid (CSF) played an important role in mediating the magnetically induced stimulating currents. Finally, with transcranial magnetic stimulation of the facial motor cortex, clearly discernible CMAPs could be produced when voluntary activation of several facial muscles was used to facilitate the responses. From this, a central motor conduction time of 5.1 ms was calculated (SD 0.60, 6 subjects).     

Abnormal muscle responses in hemifacial spasm: F waves or trigeminal reflexes?

OBJECTIVE: In patients with hemifacial spasm (HFS), abnormal muscle responses (AMR) are frequently present. The objective of this study was to investigate whether the afferent input of AMR is mediated by antidromic facial nerve stimulation or orthodromic trigeminal nerve stimulation. METHODS: AMR in the orbicularis oris muscle were recorded in 28 patients with HFS. When AMR were present, they were recorded after subthreshold stimulation of the facial nerve and weak stimulation delivered to the skin. RESULTS: AMR were recordable in 24 (86%) of the patients, and usually consisted of the early constant component (mean onset latency, 10.0 ms) and late variable component (35.3 ms), similar to R1 and R2 of the blink reflex. The early or late components of AMR, or both, were frequently elicited after subthreshold stimulation of the facial nerve (43%) and skin stimulation (88%). CONCLUSIONS: AMR are likely to be mediated by trigeminal afferent inputs, rather than antidromic activation of the facial nerve, and are a type of trigeminal reflex.     

Ultrasound-guided needle positioning near the sciatic nerve to elicit compound muscle action potentials from the gastrocnemius muscle of the rat

The use of ultrasound-guided electrode positioning in near-nerve myography was investigated. This is a minimally invasive technique that allows repeated measurements to increase accuracy and hence decreases animal numbers. Ultrasound imaging of the sciatic nerve was performed in nine rats using a 55 MHz high-end transducer. Once visualised, a monopolar needle electrode was placed through the skin near this nerve. Upon stimulation, two surface electrodes, placed over the gastrocnemius muscle, recorded compound muscle action potentials (CMAPs). Reproducibility was tested having two teams of investigators perform the recordings consecutively. Reliability of the procedure was determined by comparing the ultrasound method to the conventional technique, which requires an incision through muscle and skin to expose the sciatic nerve. In all animals the sciatic nerve was visible on ultrasound images. Both methods showed CMAP latencies (duration was determined as the time interval between the onset latency and positive peak). The conventional method had a mean latency of 3.4±0.5 ms, our method had a mean latency of 3.3±0.5 ms. Reproducibility was excellent (observed latencies and amplitudes: 3.3 versus 3.3 ms and 25.6±5.1 mV versus 22.5±8.8 mV) resulting in a coefficient of variation for duration of 2.1% and for amplitude 6.7%. Interclass correlation coefficient was 0.828 for duration. Comparing the three different measurements no significant differences were found and our new method can therefore be considered reliable and comparable to the conventional method. Ultrasound-guided near-nerve needle positioning is a reproducible and reliable minimally invasive method for selectively eliciting CMAPs, which allows repeated CMAP measurements for studying nerve regeneration in rats.     

Evaluation of proximal facial nerve conduction by transcranial magnetic stimulation.

A magnetic stimulator was used for direct transcutaneous stimulation of the intracranial portion of the facial nerve in 15 normal subjects and in patients with Bell's palsy, demyelinating neuropathy, traumatic facial palsy and pontine glioma. Compound muscle action potentials (CMAPs) thus elicited in the orbicularis oris muscle of controls were of similar amplitude but longer latency (1.3 SD 0.15 ms) compared with CMAPs produced by conventional electrical stimulation at the stylomastoid foramen. No response to magnetic stimulation could be recorded from the affected side in 15 of 16 patients with Bell's palsy. Serial studies in two patients demonstrated that the facial nerve remained inexcitable by magnetic stimulation despite marked improvement in clinical function. In the patient with a pontine glioma, the CMAP elicited by transcranial magnetic stimulation was of low amplitude but normal latency. In six of seven patients with demyelinating neuropathy, the response to intracranial magnetic stimulation was significantly delayed. Magnetic stimulation produced no response in either patient with traumatic facial palsy. Although the precise site of facial nerve stimulation is uncertain, evidence points to the labyrinthine segment of the facial canal as the most likely location.     

No clinical or neurophysiological evidence of botulinum toxin diffusion to non-injected muscles in patients with hemifacial spasm

Botulinum toxin injected into a muscle may diffuse to nearby muscles thus producing unwanted effects. In patients with hemifacial spasm, we evaluated clinically and neurophysiologically, whether botulinum toxin type A (BoNT-A) diffuses from the injection site (orbicularis oculi) to untreated muscles (orbicularis oris from the affected side and orbicularis oculi and oris from the unaffected side). We studied 38 patients with idiopathic hemifacial spasm. Botulinum toxin was injected into the affected orbicularis oculi muscle alone (at 3 standardized sites) at a clinically effective dose. Patients were studied before (T0) and 3-4 weeks after treatment (T1). We evaluated the clinical effects of botulinum toxin and muscle strength in the affected and unaffected muscles. We also assessed the peak-to-peak amplitude compound muscle action potential (CMAP) recorded from the orbicularis oculi and orbicularis oris muscles on both sides after supramaximal electrical stimulation of the facial nerve at the stylomastoid foramen. In all patients, botulinum toxin treatment reduced muscle spasms in the injected orbicularis oculi muscle and induced no muscle weakness in the other facial muscles. The CMAP amplitude significantly decreased in the injected orbicularis oculi muscle, but remained unchanged in the other facial muscles (orbicularis oris muscle on the affected side and contra-lateral unaffected muscles). In conclusion, in patients with hemifacial spasm, botulinum toxin, at a clinically effective dose, induces no clinical signs of diffusion and does not reduce the CMAP size in the nearby untreated orbicularis oris or contralateral facial muscles.     

Anterior interosseous nerve conduction study: normative data

Neurophysiological techniques assessing anterior interosseous nerve (AIN) function and employing surface electrode recordings from the flexor pollicis longus (FPL), have been limited by technical difficulties. The aim of this study was to describe a surface electrode recording technique of investigating the AIN by recording compound muscle action potentials (CMAPs) from FPL. CMAP responses exhibited a negative onset, suggesting that they originated from FPL, and this was confirmed by needle recording. Normative data has been established that may prove useful in future studies assessing pathological involvement of the anterior interosseous nerve.     

Contralateral reinnervation of midline muscles in facial paralysis.

We report on a patient with recovery of activity of the left orbicularis oris and nasalis muscles 3 months after a complete left facial palsy. Stimulation of the affected facial nerve evoked no responses, whereas contralateral facial nerve stimulation showed polyphasic responses with very long latencies in the nasalis and orbicularis oris muscles. Needle electromyography (EMG) revealed abnormal spontaneous activity in the left orbicularis oris muscle. The motor unit action potentials on the left side of the face could be recruited only during marked contraction of the corresponding muscles on the right and were of low voltage and polyphasic ("nascent potentials"). Contralateral reinnervation is probably due to sprouting of terminal branches crossing the midline of the face and innervating bundles of muscle fibers on the affected side. This phenomenon seems unfamiliar to most clinicians. Whether the activity is due to conduction along nerve fibers or muscle fibers crossing the midline is discussed.     

Electrophysiological characteristics of motor units and muscle fibers in trained and untrained young male subjects

We hypothesized that the amplitudes of compound muscle action potentials (CMAPs) and interference pattern analysis (IPA) would be larger in trained subjects compared with untrained subjects, possibly due to hypertrophy of muscle fibers and/or increased central drive. Moreover, we hypothesized that the untrained muscle is less excitable compared with the trained muscle. An electromyographic (EMG) needle electrode was used to record the IPA at maximal voluntary effort. The CMAP was obtained by stimulating the musculocutaneous nerve and recording the brachial biceps muscle using surface electrodes. CMAPs were obtained by direct muscle stimulation (DMS) with two stainless‐steel subdermal electrodes placed subcutaneously in the distal third of the muscle. Amplitudes of CMAP and IPA were significantly larger in trained subjects compared with untrained subjects. We found no differences between trained and untrained subjects in IPA power spectrum and turns per second or amplitude of the CMAPs obtained by DMS. Muscle fiber hypertrophy and/or altered central drive may account for our results, but there was no indication of changes in muscle fiber excitability. Muscle Nerve, 2010     

Significance of magnetic coil position in peripheral motor nerve stimulation

The influences of coil position and coil-nerve distance on compound muscle action potentials (CMAPs), recorded from the first dorsal interosseus muscle during magnetic stimulation of the brachial segment of the ulnar nerve, were studied in 10 healthy volunteers. A 14-cm coil was held tangentially to the skin with the center overlying the nerve. Mapping of the CMAP latencies and amplitudes was made as the coil was displaced laterally in steps of 1 cm and in planes 0-3 cm from the skin surface. Stimulation with the coil center positioned 3 cm laterally to the nerve with the coil current directed proximally yielded the largest amplitudes with minimal variability and the most constant relationship to electrically evoked CMAPs. In this position the interindividual and intraindividual reproducibility of the magnetically evoked latencies were at least as good as those of electric stimulation when coil-skin distance was less than or equal to 2 cm.     

Assessment of motor pathways to masticatory muscles: An examination technique using electrical and magnetic stimulation

To study motor pathways to masticatory muscles, a new recording technique using surface electrodes was developed. The recording electrode was mounted on a spatula and inserted enorally into the pterygomandibular plica over the belly of m. masseter. Using this technique, mean latencies/amplitudes of the compound action potentials (CMAPs) in 18 healthy subjects were 1.2 ms/4.9 mV after electrical stimulation of the trigeminal nerve below the zygomatic arch, and 5.5 ms/1.1 mV after magnetic stimulation of the cortex. In 15 patients with unilateral lesions of the facial nerve, masticatory CMAPs had virtually symmetrical configuration, latency, and amplitude, excluding a major contribution of volume conducted activity from other cranial muscles. The technique was evaluated in patients after surgical treatment for trigeminal neuralgia. Patients with with retrogasserian thermocoagulation and central demyelinating lesions were consistently identified. © 1994 John Wiley & Sons, Inc.     

Estimation of facial central motor delay by electrical stimulation of the motor cortex of the dog.

Central delay time (CD) has been estimated for activation of limb muscles by electrical or transcranial magnetic coil (TMC) stimulation of motor cortex and ventral root outflow. In the present study, we used surface electrical stimulation of the motor cortex of the right hemisphere to produce evoked compound muscle action potentials (CMAP) from the contralateral orbicularis oris (o.r.), and orbicularis oculi (o.c.), in dogs. Monopolar electrical stimulation of the facial nerve at the cerebello-pontine (CP) angle yielded CMAP activation of ipsilateral facial muscles. These latencies when subtracted from those obtained by direct cortical stimulation established CD for activation of the seventh cranial nerve. Preliminary data with single pulse magnetic stimulation at high outputs (greater than 80%) revealed CMAP with onset latencies similar to the direct facial nerve stimulation at the CP angle by electrical means.     

Blink reflexes and lateral spreading in patients with synkinesia after Bell's palsy and in hemifacial spasm

We compared various electrodiagnostical tests in patients with hemifacial spasm and in patients who developed synkinesia after Bell's palsy. We examined the evoked blink reflexes in the orbicularis oculi (o. oculi) and orbicularis oris (o. oris) muscles in 23 patients with hemifacial spasm (HFS), in 10 patients with synkinesia after Bell's palsy (BPS) and in 22 control subjects. In the patient groups, we recorded synkinesia, latency and amplitude of compound muscle action potential (CMAP) in the mental muscle after stimulation of the facial nerve and we examined electromyographic activity of the o. oculi and mental muscles synchronously. Furthermore, we studied the phenomenon of lateral spreading, also known as ephaptic transmission, between the different facial nerve branches. Patients with BPS had a prolonged R1 latency on the affected side in o. oculi and smaller mental CMAP amplitude as an indication of facial nerve damage and nerve fiber loss. This was not found in patients with HFS, who showed an increased amplitude of the R1 and R2 responses in o. oris. Patients with BPS showed only an increased R1 amplitude in o. oris. All patients had signs of synkinesia. Lateral spreading with different patterns was present in all patients with HFS and in half of the patients with BPS. Latencies of early and late responses showed no differences between HFS and BPS. In addition to alterations in facial nucleus excitability in both conditions, ectopic re-excitation of facial nerve axons in HFS may explain the differences in neurophysiological findings between HFS and BPS patients. A loss of control following synaptic stripping may also be a contributing factor.     

建立人工面神经反射弧恢复失神经支配眼轮匝肌的闭眼功能

目的：建立人工面神经反射弧,恢复面瘫兔的闭眼功能。 方法：试验动物为新西兰兔12只。采用手术切断面神经制备单侧周围性面瘫模型,患侧行肌电图检查确诊。术后第5天患侧植入刺激电极,健侧植入采集电极并留置1月。患侧分别于术后第7天、第28天给予电流刺激;而健侧采集电极则连续采集2周的肌电信号。建立健侧眼轮匝肌肌电信号采集、中枢信号处理模式识别、患侧电流刺激眼轮匝肌系统。当健侧眼轮匝肌采集的肌电信号经信号识别、提取以及电脑分析判断,符合其闭眼刺激阈值时,即对人工电刺激器发出指令,由刺激电极直接作用于患侧眼轮匝肌,引起眼睑完全闭合。结果：刺激方式为正负方向矩形波,电流强度为0.40—0.70mA之间可引起患侧眼轮匝肌收缩,眼睑完全闭合。当健侧眼睑闭合时,其肌电信号电压大于50uV,触发电刺激器,电流刺激即引发患侧眼轮匝肌收缩,完成眼睑闭合。结论：利用MEMS技术,在面瘫兔模型建立“人工面神经反射弧”,恢复患侧眼轮匝肌闭眼功能。     

The role of facial nerve conduction studies and electromyography in predicting the outcome of Bell's palsy

Many electrophysiological tests have been used to determine prognosis and extent of recovery in Bell's palsy but the reliability and sensitivity of the different parameters used is still controversial. We performed bilateral percutaneous facial nerve conduction studies, and volitional needle electromyography on 23 patients within 10–14 days post onset of their Bell's palsy. The following parameters were assessed: denervation and recruitment of the frontalis and orbicularis oris muscles, latency of the compound muscle action potential (CMAP), and CMAP amplitude ratio. The patients were re-examined 6 months later and their recovery graded according to the House-Brackman classification. The CMAP amplitude ratio and the recruitment scores of the frontalis and orbicularis oris muscles were the only parameters to reliably predict outcome (p = 0.016, 0.007 and 0.036, respectively). All patients with a CMAP amplitude ratio above 10% had a complete recovery. Since Bell's palsy is probably caused by herpes simplex virus, the active disease process is completed within 10–14 days; therefore, facial nerve conduction studies and electromyography at that time are appropriate to predict prognosis.     

Quantitative ultrasonography of facial muscles in patients with chronic facial palsy

Introduction: In this study we introduce quantitative facial muscle ultrasound as a diagnostic tool for patients with chronic unilateral facial palsy. Methods: Muscle area, thickness, and echo intensity of 6 facial muscles (frontalis, orbicularis oculi, orbicularis oris, depressor anguli oris, depressor labii inferioris, and mentalis) and of 2 chewing muscles (temporalis and masseter, as controls) were measured in 20 patients with chronic facial palsy. Results: Aside from 1, all facial muscles were significantly smaller on the paralyzed side. With exception of frontalis and orbicularis oculi muscles, all other facial muscles showed significantly higher echo intensity on the affected side. Muscle size and echo intensity of the chewing muscles showed no side‐to‐side asymmetry. Conclusions: Quantitative ultrasound of facial muscles helps to better characterize their status in patients with chronic facial palsy in the phase of denervation and during regeneration. Muscle Nerve 50 : 358–365, 2014     

Quantitative ultrasonography of facial muscles

Introduction: There is no standardized method for examination of facial muscles with ultrasound. The purpose of this study was to identify those facial muscles accessible for reliable identification and to provide reference data. Methods: In healthy subjects all facial muscles were screened for visibility, separation from adjacent muscles, and reliability of landmarks. Bilateral scans of reliable muscles were performed in 40 adult volunteers. Results: Six facial muscles were clearly demarcated with ultrasound. These were: frontalis, orbicularis oculi, orbicularis oris, depressor anguli oris, depressor labii inferioris, and mentalis muscles. Cross-sectional area and muscle thickness showed gender differences and were independently related to age for some muscles. A significant left–right side difference was only seen for the orbicularis oculi muscle in women. Conclusions: These data demonstrate the usefulness of ultrasonography to assess facial muscles and provide reference values that can be applied in the clinical setting. Muscle Nerve 47: 878–883, 2013     

Electrophysiological study of congenital facial paralysis

The common cause of neonatal facial asymmetry is facial nerve paralysis or "asymmetric crying facies syndrome". In the not uncommon later the lower lip, symmetrical at rest, becomes tilted to the so-called normal side when the patient is smiling or crying, as the congenital hypogenesis of sublabial muscles fail to pull down the lower lip in the opposite side. The electrophysiological differentiation between the two diseases has been performed by orbicularis oculi and oris reflexes with mechanically glabellar and supralabial tapping stimulation, respectively, in addition to needle and/or surface EMG recording. In the facial nerve paralysis of the case 1, R1 and R2 were absent in the orbicularis oculi and oris reflexes. EMG activity was completely lacking over the M. orbicularis oculi and oris innervated by facial nerve. On the contrary, the orbicularis oculi and oris reflexes were normal in the asymmetric crying facial of the case 2. EMG activity was absent only in the sublabial muscles including M. depressor anguli oris and/or M. depressor labii inferioris. Furthermore, needle EMG disclosed no spontaneous activity at rest, which was suggestive of no denervation in the sublabial muscles. It was, however, not possible to determine exactly which muscle the needle was inserted, the M. deprossor anguli oris or the M. depressor labii inferioris. The case 3 might be a variant of asymmetric crying facies with hypogenesis of M. orbicularis oris and/or oculi as well as the sublabial muscle, since the latency was normal but the amplitude was significantly attenuated in the components of orbicularis oculi and oris reflexes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of recording site on CMAP amplitude and on its variation over a length of nerve

The distinctions between blocking, abnormal temporal dispersion, and normal conduction require delineation of the normal change in amplitude of the compound muscle action potential (CMAP) over a length of nerve. Effects of the recording site on CMAP amplitude and on its variation were studied in median and ulnar nerves of 13 healthy subjects. CMAPs were recorded from three sites: halfway along the muscles and 1 cm distal and proximal. Elbow–wrist amplitude percentages (CMAP%) were calculated. CMAP amplitudes varied considerably between sites and subjects. Amplitudes were maximal at the middle site in only 16 of 26 nerves. The site of maximal amplitude could not be identified on the basis of thumb anatomy. CMAP% was not related to CMAP amplitude, and differed by up to 32% between adjacent sites. CMAP formation involves spatial factors (electrode site, limb position, and limb anatomy), temporal factors (dispersion), and their interaction, explaining why CMAP% can exceed 100%. The site of the recording electrode affects CMAP amplitude and CMAP% to clinically relevant degrees. Standardisation of the recording site may improve reliability of CMAP% studies. © 1994 John Wiley & Sons, Inc.     

Repetitive nerve stimulation of the nasalis muscle: technique and normal values

A technique of repetitive nerve stimulation of the facial nerve with recording from the nasalis and orbicularis oculi muscles was developed and tested in 15 healthy subjects. Quality criteria were that the stimulus artifact should return to baseline before the onset of the compound muscle action potential (CMAP), and that the CMAP should begin with a negative phase, be biphasic in shape, and have an amplitude of over 1 mV. Repetitive nerve stimulation was only performed if all four criteria were met, which was the case in all 15 subjects for the nasalis muscle, but in only 5 subjects for the orbicularis oculi muscle. The largest observed decrement was 9% in area. Reptitive nerve stimulation of the nasalis muscle is thus feasible, but its diagnostic utility remains to be established in patients with disorders of neuromuscular transmission.     

面肌痉挛显微血管减压术的诱发肌电图监测和评估

目的:探讨面神经诱发肌电图在显微血管减压(MVD)术中、术后对面肌痉挛治疗效果的监测和评估。方法:对26例典型面肌痉挛病人、探讨在MVD术前、术中、术后,经皮刺激痉挛侧(手术侧)面神经下颌缘支,记录诱发同侧眼轮匝肌肌电位(MD-OC反应)变化,并以正常侧作对照检查。结果:26例术前均记录到痉挛侧MD-OC反应,在术中操作不同阶段,21例均见MD-OC反应消失。术后1周～3个月随访复查21例中,12例痉挛完全消失,MD-OC反应不复存在,9例症状明显或部分减轻,但有4例再记录到MD-OC反应。另5例术中,术后均记录到MD-OC反应,症状未有改善。结论:面神经诱发肌电图运用于MVD术中监测和预后判断,可改善和提高面肌痉挛的治愈率。