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.     

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     

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     

Trigemino-facial reflex inhibitory responses in some lower facial muscles

The effects of electrical trigeminal stimulation on activated facial muscles were studied in 20 normal subjects in order to evaluate whether excitatory or inhibitory responses are present and to investigate whether the reflex organization is similar in all the facial muscles. No inhibition was observed in frontalis, orbicularis oculi, orbicularis oris, and mentalis muscles. By contrast, a clear suppression of electromyographic (EMG) activity (late silent period or SP2) was present in the levator labii superioris, depressor anguli oris, and depressor labii inferioris muscles, with a mean latency ranging from 41.8 to 50.2 ms, and a mean duration ranging from 27.5 to 40.9 ms. An early suppression of EMG activity (early silent period or SP1) was observed, with a latency of 16 to 20 ms and a duration of 10 ms, mainly in inferior perioral muscles. Our findings show a selective trigeminal inhibitory influence upon some specific lower facial muscles.     

Somatotopic organization of perioral musculature innervation within the pig facial motor nucleus

The orbicularis oris and buccinator muscles of mammals form an important subset of the facial musculature, the perioral muscles. In many taxa, these muscles form a robust muscular hydrostat capable of highly manipulative fine motor movements, likely accompanied by a specialized pattern of innervation. We conducted a retrograde nerve-tracing study of cranial nerve (CN) VII in pigs (Sus scrofa) to: (1) map the motor neuron pool distributions of the superior and inferior orbicularis oris, and the buccinator, to test the hypothesis that perioral muscle motor neuron pools exhibit a somatotopic organization within the facial motor nucleus; and (2) test the hypothesis that portions of the superior orbicularis oris (SOO) motor neuron pool also exhibit a somatotopic organization, reflecting a potential compartmentalization of function of the rostral, middle, and caudal segments of this muscle. Cresyl violet histological staining showed that the pig facial motor nucleus was comprised of 7 well-defined subnuclei. Neuroanatomical tracers injected into these perioral muscles transported to the motor neuron pools of the lateral 4 of the 7 subnuclei of the facial motor nucleus. The motor neuron pools of the perioral muscles were generally segregated from motoneurons innervating other facial muscles of the rostrum. However, motor neuron pools were not confined to single nuclei but instead spanned across 3-4 subnuclei. Perioral muscle motor neuron pools overlapped but were organized somatotopically. Motor neuron pools of portions of the SOO overlapped greatly with each other but exhibited a crude somatotopy within the SOO motor neuron pool. The large and somatotopically organized SOO motor neuron pool in pigs suggests that the upper lip might be more richly innervated than the other perioral muscles and functionally divided.     

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).     

Turns amplitude analysis of the orbicularis oculi and oris muscles.

OBJECTIVE: The aim of the study was to determine whether 'clouds' from turns amplitude analysis obtained from the orbicularis oculi and oris muscles without force monitoring can be used to differentiate pathological processes affecting the face. METHODS: The interference pattern from orbicularis oculi and orbicularis oris was studied using a concentric needle electrode. Data-points from 20 normal subjects were plotted on a logarithmic scale of mean amplitude between turns versus turns/second, from which linear regression analysis defined the 95% confidence intervals. This enabled us to draw the boundaries of the normal cloud on a linear plot. Data-points from the interference pattern in two pathological cohorts, of 6 patients receiving botulinum toxin injections (representing a neurogenic model), and 6 patients with a muscle dystrophy (representing a myopathic model) were plotted against the normal cloud. These findings were compared and correlated with the mean durations obtained on motor unit action potential analysis from these same two facial muscles. RESULTS: The majority of patients receiving botulinum toxin injections into their facial muscles showed a pattern of high amplitude with low turns/s, or low amplitude with a low-to-normal range of turns/s in both facial muscles. These findings were associated with high-duration motor unit action potentials in most cases. In the myopathic group of patients 66% showed a pattern of low amplitude with low-to-normal range of turns/s in O oculi and O oris. This correlated with short-duration motor unit action potentials in both facial muscles. CONCLUSIONS: We have demonstrated that turns amplitude analysis without force monitoring can be used to study the interference pattern from facial muscles and can be applied to differentiate primary neurogenic from myopathic pathological processes. SIGNIFICANCE: Turns amplitude analysis without force monitoring in the facial muscles can be used as an effective and practical method of interference pattern analysis to complement findings from conventional motor unit action potential analysis.     

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)     

Electrophysiological study of ephaptic axono-axonal responses in hemifacial spasm

One of the classic features of hemifacial spasm (HFS) is spread of the blink reflex responses to muscles other than the orbicularis oculi. The pathophysiological mechanisms underlying the generation of such abnormal responses include lateral spread of activity between neighboring fibers of the facial nerve and hyperexcitability of facial motoneurons. In this report we present evidence for another mechanism that can contribute to the generation of responses in lower facial muscles resembling the R1 response of the blink reflex. In 13 HFS patients, we studied the responses induced in orbicularis oris by electrical stimuli applied at various sites between the supraorbital and zygomatic areas. We identified responses with two different components: an early and very stable component, with an onset latency ranging from 10.5 to 14.8 ms, and a more irregular longer-latency component. Displacement of the stimulation site away from the supraorbital nerve and towards the extracranial origin of the facial nerve caused a progressive shortening of response latency. These features indicate that, in our patients, the shortest latency component of the orbicularis oris response was likely generated by antidromic conduction in facial nerve motor axons followed by axono-axonal activation of the fibers innervating the lower facial muscles. Our results suggest that motor axono-axonal responses are generated by stimulation of facial nerve terminals in HFS.     

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.     

Prognostic value of minimal excitability of facial nerve in Bell's palsy.

Nerve excitability is useful for prognosis in Bell's palsy. Minimal excitability values (MEV) were obtained by stimulating the facial nerve and recording the effective current (mA) required to evoke a minimal visible contraction of frontalis, orbicularis oculi, orbicularis oris, and mentalis muscles respectively. Serial MEVs were performed on 100 patients with facial palsy, of whom 87 were followed for six months or to complete recovery; 61 patients were treated with steroids of whom 57 had good recovery. Serial MEVs were not only useful for prognosis, but also helpful in regulating the dosage of prednisone.     

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.     

Reciprocal innervation of motoneurons lacking Ia input in man

A clear pattern of reciprocal innervation was found among the orbicularis oculi and the frontalis muscles in man during voluntary contractions. In contrast, facial afferent input was shown to be devoid of reciprocal action on these muscles. The results indicate a lack of γ control in facial muscles.     

Nuclear magnetic resonance imaging in a case of facial myokymia with multiple sclerosis

A 59-year-old female of facial myokymia with multiple sclerosis was reported. In this case, facial myokymia appeared at the same time as the first attack of multiple sclerosis, in association with paroxysmal pain and desesthesia of the neck, painful tonic seizures of the right upper and lower extremities and cervical transverse myelopathy. The facial myokymia consisted of grossly visible, continuous, fine and worm-like movement, which often began in the area of the left orbicularis oculi and spread to the other facial muscles on one side. Electromyographic studies revealed grouping of motor units and continuous spontaneous rhythmic discharges in the left orbicularis oris suggesting facial myokymia, but there were no abnormalities on voluntary contraction. Sometimes doublet or multiplet patterns occurred while at other times the bursts were of single motor potential. The respective frequencies were 3-4/sec and 40-50/sec. There was no evidence of fibrillation. The facial myokymia disappeared after 4-8 weeks of administration of prednisolone and did not recur. In the remission stage after disappearance of the facial myokymia, nuclear magnetic resonance (NMR) imaging by the inversion recovery method demonstrated low intensity demyelinated plaque in the left lateral tegmentum of the inferior pons, which was responsible for the facial myokymia, but X-ray computed tomography revealed no pathological findings. The demyelinated plaque demonstrated by NMR imaging seemed to be located in the infranuclear area of the facial nerve nucleus and to involve the intramedurally root.(ABSTRACT TRUNCATED AT 250 WORDS)     

A new method for measuring compound muscle action potentials in facial palsy: a preliminary study

To establish a simple, reproducible procedure for studying facial motor nerve conduction (MNC), we determined the optimal electrode position to record evoked compound muscle action potentials (CMAPs) from perioral muscles in normal subjects. We examined three new electrode positions in which the electrode connected to the one input of the amplifier was placed on the mental protuberance, and the one connected to the other input was placed on the skin over the orbicularis oris muscle (the philtrum, mouth angle, or lower lip). We then compared the morphology and amplitudes of the CMAPs, right-left differences, and the reproducibility of CMAP amplitudes with recordings taken from the standard electrode position in which one electrode was placed on the nasolabial fold closely lateral to the ala nasi, and the other was placed on the skin over the orbicularis oris. Percutaneous supramaximal electrical stimulation was applied to the main trunk of the facial nerve. All three of the new recording positions showed greater amplitudes and more obvious biphasic CMAPs than the standard method. Positioning the electrode connected to the negative input on the philtrum was optimal in terms of right-left differences and the reproducibility of CMAP amplitudes. Therefore, this midline recording is a simple, reproducible method for calculating the CMAP amplitude ratio. However, prior to clinical use of this procedure, analyses of patients with facial palsy are required.     

Organization of the facial nucleus and corticofacial projection in the monkey: a reconsideration of the upper motor neuron facial palsy

The somatotopic organization of the facial nucleus and the distribution of the corticofacial projection in the monkey were studied by the use of retrograde and anterograde transport of horseradish peroxidase. Facial motor neurons innervating lower facial muscles were primarily found in the lateral part of the nucleus, those supplying upper facial muscles in the dorsal part of the nucleus, and those innervating the platysma and posterior auricular muscles in the medial part of the nucleus. Descending corticofacial fibers innervated the lower facial motor nuclear region bilaterally, although with contralateral predominance. The upper facial motor nuclear regions received scant direct cortical innervation on either side of the brain. Our results indicate that upper facial movement, like that at the shoulder, is relatively preserved in upper motor neuron palsy because these motor neurons receive little direct cortical input. By contrast, the lower facial muscles, like those of the hand, are more severely affected because their motor neurons normally depend upon significant cortical innervation.     

Crossed linguo-buccal reflex in post-stroke patients

A pathological crossed orofacial reflex, called crossed linguo-buccal reflex in the present study, was observed in approximately 1/3 of post-stroke patients with central facial palsy. Stroking with pressure two or three times with a split wooden tongue-blade to the tongue or palate contralateral to the central facial palsy elicited a reflex movement consisting of retraction of the angle of mouth and medio-posterior withdrawal of the buccal mucosa on the paretic side. Seventy-seven patients with central hemifacial palsy caused by a unilateral cerebral lesion were examined clinically, electromyographically and by computed tomography (CT) and magnetic resonance imaging (MRI). In addition, three men with bilateral cerebral lesions and bilateral crossed linguo-buccal reflexes were electromyographically examined. Twenty-two patients with unilateral cerebral lesions had this reflex. It was found that this reflex was most frequently observed in patients with a capsulo-caudate lesion involving the head of the caudate nucleus, the anterior limb and genu of the internal capsule. The electromyogram of the reflex showed increased activity in the orbicularis oris, depressor anguli oris, risorius, zygomaticus major and buccinator muscles on the paretic side with a long latency (254-856 ms), and a prolonged after-discharge after the stimulation. Reciprocal inhibition was observed in patients with bilateral positive reflexes. These findings suggest that liberation of the polysynaptic brainstem reflex in the medulla oblongata and pons from the indirect corticobulbar inhibition may underlie the occurrence of the crossed linguo-buccal reflex in post-stroke patients.     

Inhibitory reflexes in human perioral facial muscles: a single-motor unit study.

OBJECTIVE: To describe the reflex responses evoked by trigeminal stimulation in perioral facial motor units (MUs) in humans. METHODS: We recorded single motor units (MUs) from perioral muscles performing three movements: elevation of the upper lip (levator labii superioris muscle--LLS), protrusion of the lips (orbicularis oris muscle--OOr) and depression of the lower lip (depressor anguli oris and depressor labii inferioris muscles--DAO/DLI) with concentric needle electrodes. MUs were tested during constant voluntary activation with non-painful cutaneous electrical stimuli applied to the mental or supraorbital nerves and intraorally. Analysis was performed with peristimulus histograms and cumulative sum. RESULTS: Eighty MUs were sampled from 17 subjects. Cutaneous stimulation induced inhibition of discharge in 100% of the lip-depressor MUs, inhibition in 65-70% of LLS MUs and in 25% of OOr MUs. Mean latency of inhibition was of 35+/-12ms. Intraoral stimulation produced an equivalent percentage of inhibitory or facilitatory effects with no difference among the three muscles. CONCLUSIONS: Reflex responses to cutaneous stimulation identify a completely inhibitory (DAO/DLI), a mainly inhibitory (LLS) and a mixed (OOr) pattern in perioral muscles. SIGNIFICANCE: A purely inhibitory trigemino-facial reflex is present in lip-lowering muscles with potential use in clinical practice.     

Spastic paretic hemifacial contracture (SPHC) in a patient with multiple sclerosis. A clinical, EMG and neuroimaging study.

We present the case of a 42-year-old woman with a 4-year history of definite multiple sclerosis (MS) and sustained contracture of the left hemiface with marked left deviation of the nose, deepened left nasolabial groove, narrowed palpebral fissure and weakness of the contracting muscles. Needle electromyography showed continuous resting activity of irregularly firing motor unit potentials (MUP) in the left orbicularis oculi (OO) and orbicularis oris, but not in the left frontalis. Simultaneous recording of maximal voluntary contraction of the OO on both sides showed marked preponderance on the right. Blink reflex findings were consistent with an injury in the pons, mainly in the vicinity of the left facial nucleus. A magnetic resonance imaging study showed multiple supra- and infra-tentorial white matter lesions, as well as multiple lesions at the level of the pons. Complete recovery was observed after 3 months. This condition has been described in cases of brainstem tumor as spastic paretic hemifacial contracture (SPHC). Up to now SPHC has not been explicitly associated with MS and, in this case, it could be arguably attributed to hyperexcitability of the facial neurons due to demyelination of the corticofacial fibers.     

Mechanically evoked perioral reflexes in infants

Mechanically evoked activity in the superior and inferior segments of the orbicularis oris muscle was sampled in several young infants using a specially designed position-servo linear motor and a pacifier instrumented with eight miniature EMG electrodes. Unilateral stimulation of lip vermilion resulted in short latency, bilateral activation of the upper and lower lip recording sites. The ontogenesis of facial reflex sensitivity to mechanical inputs is discussed in relation to the acquisition of motor skills, including speech and smiling.