Blink reflex in patients with hemifacial spasm. Observations during microvascular decompression operations

The blink reflex cannot normally be elicited during surgical anesthesia using inhalation anesthetics. However, in patients with hemifacial spasm (HFS) the early component of the reflex response (R1) can be elicited on the affected side but not on the unaffected side during such anesthesia. The electromyographic (EMG) response from the mentalis muscle to stimulation of the supraorbital nerve was recorded during microvascular decompression (MVD) of the facial nerve to relieve HFS and compared to the response from the same muscle to stimulation of the zygomatic branch of the facial nerve in four patients. During the operation before the facial nerve was decompressed, contractions in both the orbicularis oculi and the mentalis muscles could be elicited by stimulation of the supraorbital nerve (mean latencies 12.2 +/- 1.9 and 12.9 +/- 2.0 ms, respectively). When the facial nerve had been decompressed the blink reflex could no longer be elicited, and there was no response from the mentalis muscle to stimulation of the zygomatic branch of the facial nerve. Compound action potentials (CAP) recorded from the 7th cranial nerve in response to stimulation of the supraorbital nerve had latencies of 7.5 ms +/- 1.4 ms to the negative peak.     

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.     

Reflexes elicited from cutaneous and mucosal trigeminal afferents in normal human subjects

It has been shown that in patients in whom the central stump of the hypoglossal nerve has been anastomosed to the peripheral stump of a lesioned facial nerve, supraorbital nerve stimulation can elicit a short-latency reflex (12.5±0.6 ms; mean±S.D.) in facial muscles similar to the R1 disynaptic blink reflex response, but not followed by an R2 blink reflex component⁴⁶. Thus in addition to replacing the facial neurons at peripheral synapses, these hypoglossal nerves contribute to a trigemino-hypoglossal reflex. The aim of this work was to study the type of reflex activities which can be elicited in both facial and tongue muscles by electrical stimulation of cutaneous (supraorbital nerve) or mucosal (lingual nerve) trigeminal (V) afferents in normal subjects. The results show that although stimulation of cutaneous V1 afferents elicits the well-known double component (R1–R2) blink reflex response in the orbicularis oculi muscles, it does not produce any detectable reflex response in the genioglossus muscle, even during experimental paradigms designed to facilitate the reflex activity. Conversely, stimulation of mucosal V3 afferents can elicit a single reflex response of the R1 type in the genioglossus muscle but not in the orbicularis oculi muscles, even during experimental paradigms designed to facilitate the reflex activity. These data are discussed in terms of two similar but separate circuits for the R1 responses of cutaneous (blink reflex) and mucosal (tongue reflex) origins. They suggest that in patients with hypoglossal-facial (XII–VII) nerve anastomosis, the short-latency trigemino-‘hypoglossal-facial' reflex of the R1 blink reflex type observed in facial muscles following supraorbital nerve stimulation could be due to changes in synaptic effectiveness of the central connectivity within the principal trigeminal nucleus where both cutaneous and mucosal trigeminal afferents project.     

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.     

Further evidence for a central reorganisation of synaptic connectivity in patients with hypoglossal-facial anastomosis in man

In normal subjects, electrical stimulation of trigeminal mucosal afferents (lingual nerve - V3) can elicit a short latency (12.5+/-0. 3 ms; mean+/-S.D.) reflex response in the ipsilateral genioglossus muscle (Maisonobe et al., Reflexes elicited from cutaneous and mucosal trigeminal afferents in normal human subjects. Brain Res. 1998;810:220-228). In the present study on patients with hypoglossal-facial (XII-VII) nerve anastomoses, we were able to record similar R1-type blink reflex responses in the orbicularis oculi muscles, following stimulation of either supraorbital nerve (V1) or lingual nerve (V3) afferents. However, these responses were not present in normal control subjects. Voluntary swallowing movements produced clear-cut facilitations of the R1 blink reflex response elicited by stimulation of V1 afferents. In a conditioning-test procedure with a variable inter-stimulus interval, the R1 blink reflex response elicited by supraorbital nerve stimulation was facilitated by an ipsilateral mucosal conditioning stimulus in the V3 region. This facilitatory effect was maximal when the two stimuli (conditioning and test) were applied simultaneously. This effect was not observed on the R1 component of the blink reflex in the normal control subjects. These data strongly suggest that in patients with XII-VII anastomoses, but not in normal subjects, both cutaneous (V1) and mucosal (V3) trigeminal afferents project onto the same interneurones in the trigeminal principal sensory nucleus. This clearly supports the idea that peripheral manipulation of the VIIth and the XIIth nerves induces a plastic change within this nucleus.     

Physiological abnormalities in hemifacial spasm studied during microvascular decompression operations

The pathophysiology of hemifacial spasm was studied using electrophysiologic recordings made during neurosurgical operations to relieve it by microvascular decompression of the facial nerve near its entrance into the brain stem. Electrical stimulation of the temporal or the marginal mandibular branch of the facial nerve resulted in a response not only from the muscles that were innervated by the branch of the facial nerve that was stimulated, but also from other muscles, as evidenced by EMG recordings. This "lateral spread" of antidromic activity was facilitated by stimulation at a high rate (50 pps): the response increased five- to tenfold within a few seconds. When the repetition rate was reduced to the initial low stimulus rate (2 to 5 pps), facilitation continued for periods lasting from a few seconds to several minutes. The amplitude of the response of the supraorbital reflex (blink reflex), which can be elicited in patients with hemifacial spasm intraoperatively on the affected side despite the use of inhalation anesthesia, also increased after brief stimulation at a high rate (50 pps). After the facial nerve had been decompressed, both the lateral spread response and the blink reflex response were absent. These results support the hypothesis that hemifacial spasm is the result of hyperexcitability of the facial motor nucleus and facilitation of cross-transmissions between cells in the nucleus that innervate different parts of the face.     

The relationship of eyelid movement to the blink reflex

Although the blink reflex is a standard neurophysiological investigation its relationship with eyelid movement has not been clearly established. We studied normal subjects and patients with unilateral facial paralysis to define the pattern of eyelid movement following glabellar tap, supraorbital nerve stimulation, facial nerve stimulation and direct corneal stimulation. We found that eyelid closure did not necessarily occur in a single movement. Following glabellar tap the first component of a two-stage movement was initiated by levator palpebrae relaxation while with supraorbital nerve stimulation orbicularis oculi contraction produced the first movement. The compound muscle action potential following direct facial nerve stimulation produced only minimal eyelid movement, the major closure being associated with a longer latency orbicularis oculi reflex. Corneal stimulation elicited a single component eyelid movement. Thus, the pattern of eyelid movement differed for each stimulus reflecting variations in orbicularis oculi contraction and levator palpebrae inhibition.     

Unmasking of the trigemino-accessory reflex in accessory facial anastomosis

OBJECTIVE: To evaluate the possible blink reflex responses in facial muscles reinnervated by the accessory nerve. METHOD: Eleven patients with a complete facial palsy were submitted to a surgical repair by an accessory facial nerve anastomosis (AFA). In this pathological group, blink reflex was studied by means of percutaneous electrical stimulation of the supraorbital nerve and recording from the orbicularis oculi muscle. A control group comprised seven normal people and seven patients with a complete Bell's facial palsy; in this group, responses on the sternocleidomastoideus (SCM) muscles were studied after supraorbital nerve stimulation. RESULTS: All the patients with AFA showed a consistent degree of facial reinnervation. Ten out of the 11 patients with AFA showed reflex responses; in six, responses were configured by a double component pattern, resembling the R1 and R2 components of the blink reflex; three patients had an R1-like response and one patient showed a unique R2 component. Mean values of latencies were 15.2 (SD 4.6) ms for the R1 and 85.3 (SD 9.6) ms for the R2. In the control group, eight out of 14 people had evidence of reflex responses in the SCM muscles; these were almost exclusively configured by a bilateral late component (mean latency 63.5 (SD15.9) ms) and only one of the subjects showed an early response at 11 ms. CONCLUSION: The trigemino-accessory reflex response in the pathological group was more complex and of a significantly higher incidence than in the control group. These differences could be tentatively explained by a mechanism of synaptic plasticity induced by the impairment of the efferent portion of the reflex. This could unmask the central linking between the trigeminal and the accessory limbs of the reflex. The findings described could be a demonstration of neurobionomic function in the repairing process of the nervous system.     

Lateral spread response elicited by double stimulation in patients with hemifacial spasm

In patients with hemifacial spasm (HFS), a lateral spread response (or abnormal muscle response) is recorded from facial muscles after facial nerve stimulation. The origin of this response is not completely understood. We studied the lateral spread responses elicited by double stimulation in 12 patients with HFS during microvascular decompression. The response was recorded from the mentalis muscle by electrical stimulation of the temporal branch of the facial nerve or from the orbicularis oculi muscles by stimulation of the marginal mandibular branch. The interstimulus intervals (ISIs) of double stimulation ranged from 0.5 to 7.0 ms. R1 was defined as the response elicited by the first stimulus, and R2 as the response elicited by the second stimulus. R1 had a constant latency and amplitude regardless of the ISI, whereas R2 appeared after a fixed refractory period without facilitation or depression in a recovery curve of latency and amplitude. From these findings, we consider that the lateral spread response is due to cross-transmission of facial nerve fibers at the site of vascular compression rather than arising from facial nerve motor neurons.     

异常肌反应在面神经显微血管减压术中的应用

目的 探讨异常肌反应(abnormal muscle response,AMR)监测在面神经显微血管减压术(microvascular decolnpression,MVD)中鉴别责任血管、评估减压效果以及判断预后方面的作用.方法 241例典型面肌痉挛患者接受了面神经MVD术中AMR的实时监测,并在术后1周进行疗效评估,分析术中AMR变化与手术预后之问的关系.结果 所有241例患者均在术中记录到典型AMR波形,术后第1周217例(90.0%)患者症状完全缓解.AMR消失组175例,其中165例(94.3%)症状缓解;AMR未消失组66例,52例(78 8%)症状缓解.统计学分析显示AMR消失组的疗效明显好于AMR未消失组(P<0.05).结论 术中AMR监测可辅助判断责任血管,评估减压效果,对提高手术疗效具有较高的应用价值.

Abstract：

Objective Abnormal muscle response( AMR) to the electrical stimulation of a branch of facial nerve is a specific electrophysiological feature of primary hemifacial spasm ( HFS) .Although the correlation between intraoperative AMR findings and postoperative results in patients with HFS has been investigated before, the AMR monitoring has not been employed widely during the microvascular decompression (MVD) surgery.The aim of this study was to evaluate the value of AMR monitoring during MVD, and the correlation between the AMR changes and the clinical outcome.Method This study included 241 cases of MVD.Intraoperative AMR monitoring was performed for each subject.The patients were divided into two groups based on whether the AMR wave disappeared or not following decompression of the facial nerve.Results The AMR disappeared after MVD in 175 patients.Among these 175 patients, 165(94.3% ) patients were relieved from HFS 1 week after HFS.Out of the 66 patients in whom the AMR persisted after MVD, 52(78.8%) patients were relieved.The correlation between intraoperative AMR abolition and HFS relief was statistically significant ( P < 0.05 ) .Conclusions Intraoperative AMR monitoring is an effective assistant for a successful MVD for the patient with HFS.It may be helpful in predicting outcomes in short term and identifying offending vessels,so it should be monitored routinely during MVD.     

Corneal reflex in normal and pathological subjects

The orbicularis oculi response can be evoked both by mechanical stimulation of the cornea (corneal reflex) and by electrical stimulation of the skin overlying the supraorbital nerve (blink reflex). Mechanical stimuli to the cornea activate A delta and C free nerve endings of the corneal mucosa. Electrical stimuli to the supraorbital nerve activate A beta, A delta and C fibers of the nerve trunk. Both reflexes present a bilateral late response, but the blink reflex shows in addition an early ipsilateral component (R1), which has never been observed with the corneal stimulation in man. We have developed a simple technique of electrical stimulation of the cornea which provides stable responses and allows precise measurements of threshold and latency of the reflex. In normal subjects, the threshold ranged from 50 to 350 microA, and the maximal stimulus that the subject could bear (tolerance level) ranged from 1000 to 2500 microA. The minimal latency to tolerance level stimuli was 39 +/- 3 msec. The latency difference between the direct responses evoked from the two opposite corneas never exceeded 8 msec and the difference between the direct and consensual responses elicited from the same cornea never exceeded 5 msec. An early ipsilateral component similar to the R1 response of the blink reflex was not observed, even with supramaximal stimulation. The electrically evoked corneal reflex was normal in 10 cases of essential trigeminal neuralgia, while the responses showed significant abnormalities in 18 subjects submitted to thermocoagulation of the Gasserian ganglion as a treatment of neuralgic pain, as well as in 2 cases of symptomatic neuralgia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blink reflex recovery in facial weakness: an electrophysiologic study of adaptive changes

OBJECTIVE: To study the electrophysiologic effects of unilateral facial weakness on the excitability of the neuronal circuitry underlying blink reflex, and to localize the site of changes in blink reflex excitability that occur after facial weakness. BACKGROUND: Eyelid kinematic studies suggest that adaptive modification of the blink reflex occurs after facial weakness. Such adaptations generally optimize eye closure. A report of blepharospasm following Bell's palsy suggests that dysfunctional adaptive changes can also occur. METHODS: Blink reflex recovery was evaluated with paired stimulation of the supraorbital nerve at different interstimulus intervals. Comparisons were made between normal control subjects and patients with Bell's palsy who either recovered facial strength or who had persistent weakness. RESULTS: Blink reflex recovery was enhanced in patients with residual weakness but not in patients who recovered facial strength. Facial muscles on weak and unaffected sides showed enhancement. In patients with residual weakness, earlier blink reflex recovery occurred when stimulating the supraorbital nerve on the weak side. Sensory thresholds were symmetric. CONCLUSION: Enhancement of blink reflex recovery is dependent on ongoing facial weakness. Faster recovery when stimulating the supraorbital nerve on the paretic side suggests that sensitization may be lateralized, and suggests a role for abnormal afferent input in maintaining sensitization. Interneurons in the blink reflex pathway are the best candidates for the locus of this plasticity.     

Neurophysiological evaluation of trigeminal and facial nerves in patients with chronic inflammatory demyelinating polyneuropathy

Cranial neuropathy is clinically uncommon in patients with chronic inflammatory demyelinating polyneuropathy (CIDP), but there is little information on the neurophysiological examination of cranial nerve involvement. To determine the incidence of trigeminal and facial nerve involvement in patients with CIDP, the direct response of the orbicularis oculi muscle to percutaneous electric stimulation of the facial nerve and the blink reflex (induced by stimulation of the supraorbital nerve) were examined in 20 CIDP patients. The latency of the direct response was increased in 12 patients (60%) and an abnormal blink reflex was observed in 17 patients (85%). There was no correlation between electrophysiological findings and the latencies of the direct and R1 responses and disease duration or clinical grade in CIDP patients. Nevertheless, the prevalence of subclinical trigeminal and facial neuropathy is extremely high in patients with CIDP when examined by neurophysiological tests.     

Experimental study on the correlation between abnormal muscle responses and F waves in hemifacial spasm

OBJECTIVES: To investigate the correlation between abnormal muscle response (AMR) and F wave by establishing an animal model of hemifacial spasm (HFS). METHODS: Both demyelination in the main trunk of the facial nerve just distal to stylomastoid foramen and vascular compression were used to duplicate animal model of HFS in ten New Zealand white rabbits. AMR and F waves were elicited from the orbicularis oculi and mentalis muscles respectively by stimulating marginal mandibular branch of the facial nerve 6 weeks post-operatively. Correlation analyses were used to compare the relationship between AMR/M and F/M amplitude ratio and between the duration of AMRs and F waves. RESULTS: There was a linear correlation between the mean values of the AMR/M and F/M amplitude ratio (r=0.8602, p<0.01), which can also be found between the duration of AMRs and F waves (r=0.7702, p<0.01). DISCUSSION: Enhanced F waves and AMRs may have the same origin. The F wave can be regarded as a more direct index in the diagnosis pre-operatively, monitoring intraoperatively and follow-up post-operatively in patients with HFS.     

Cortical control of voluntary blinking: a transcranial magnetic stimulation study.

OBJECTIVE: To investigate cortical regions related to voluntary blinking. METHODS: Transcranial magnetic stimulation (TMS) was applied to the facial motor cortex (M1) and the midline frontal region (Fz) in 10 healthy subjects with eyes opened and closed. Motor-evoked potentials were recorded from the orbicularis oculi (OOC), orbicularis oris (OOR), abductor digiti minimi and tibialis anterior using surface and needle electromyography electrodes. Facial M waves and blink reflex were measured using supramaximal electrical stimulation of the facial and supraorbital nerves. RESULTS: TMS at Fz elicited 3 waves in OOC with no response in other tested muscles except for the early wave in OOR. Facial M1 stimulation produced only early and late waves. Because of their latencies, shapes, and relationship to coil position and stimulation intensity, early and late waves appeared to be analogous to the facial M wave and R1 component of the blink reflex. The intermediate wave at 6-8 ms latency was elicited in OOC by Fz stimulation with eyes closed. CONCLUSIONS: Since its latency matches the central conduction time of other cranial muscles and it has characteristic of muscle activation-related facilitation, the intermediate wave is presumably related to cortical stimulation. This result provides evidence that the cortical center for the upper facial movements, including blinking, is not principally located in the facial M1, but rather in the mesial frontal region.     

The corneal reflex and the R2 component of the blink reflex

A reflex contraction of the human orbicularis oculi muscles can be evoked by stimulation of either the supraorbital region ("blink reflex") or the cornea ("corneal reflex"). We found that the latency of the corneal reflex was longer, and the duration was longer than the R2 component of the blink reflex. The absolute refractory period of the R2 component of the blink reflex was longer after supraorbital than after corneal conditioning stimulation. When the R2 component of the blink reflex was habituated by repetitive stimuli, stimulation of the cornea still evoked a reflex, but supraorbital stimulation produced only a depressed R2 response. These findings suggest that the two reflexes do not have identical neural connections.     

Trigeminally induced startle in children with hyperekplexia.

To determine the physiological features of startle reactions in children with hereditary hyperekplexia, motor responses to auditory and trigeminal stimulation were investigated in 2 patients and 3 control subjects by means of multiple surface electromyographic recordings. The pattern of motor activation in auditory startle was similar in the two groups, although the responses in the patients were increased in terms of the extent of the responses. In the patients, nose taps elicited two separate responses in various muscles. The initial, short-latency response was often elicited in all the muscles examined. This reflex was similar to the R1 component of the electrical blink reflex. In addition, the early reflex was immediately followed by the second response, which also appeared widely and was similar to R2 of the blink reflex. Taps on the supraorbital nerve elicited multiple startle patterns consisting of these two responses, although generalization was infrequent. In the control subjects, these responses were elicited in a few muscles. In the hyperekplectic children, both the early and second responses to trigeminal stimulation were increased, in addition to the audiogenic reflex. It was suggested that enhancement of these responses occurred due to hyperexcitability in the brainstem reticular formation in our patients.     

Enhanced gain of blink reflex responses to ipsilateral supraorbital nerve afferent inputs in patients with facial nerve palsy.

OBJECTIVES: Patients with peripheral facial palsy (PFP) may present with transient hyperkinetic movement disorders in the side contralateral to the paralysis. One possible cause of such enhanced motor activity is sensitization of reflex responses to afferent inputs from the unprotected cornea. We hypothesized that if this sensitization occurs, the size of the orbicularis oculi (OOc) responses induced by afferents from the ophthalmic branch of the paralyzed side would be larger than those induced by afferents from the contralateral side. METHODS: In 68 patients with complete PFP and in a group of 30 age-matched control subjects we recorded the response of the OOc muscle of one side to electrical stimulation of the supraorbital nerve of both sides, and calculated the ratio between R2c and R2 (R2c/R2). RESULTS: The mean R2c/R2 ratio was significantly larger in patients than in control subjects (unpaired t test, P<0.05). Larger R2c than R2 responses were observed in 23.1% of control subjects and in 80.9% of patients (chi(2)=13.3, P<0.01). CONCLUSIONS: Our results suggest that patients with PFP have an enhanced blink reflex gain to inputs from the paralyzed side compared to those of the non-paralyzed side. Sensitization of the blink reflex polysynaptic pathways to inputs carried by afferent fibers from the ophthalmic branch of the paralyzed side can play a role in inducing an abnormal facial motor behavior after PFP.     

Axon reflexes or ephaptic responses simulating blink reflex R1 after XII-VII nerve anastomosis

It has been claimed that functional recovery of the blink reflex occurs after hypoglossal-facial nerve anastomosis. This has been explained through central nervous system plasticity and reorganization of neuronal connections. In 5 patients with reinnervated facial muscles after hypoglossal-facial nerve anastomosis, we observed “R1-like” responses that fulfilled criteria for facial nerve axon reflexes or ephapses. First, displacement of the stimulating electrode from the supraorbital to the zygomatic area shortened the latency of the evoked response. Second, these responses were stable (jitter mean consecutive difference < 25 μs) and they had complex potential shapes unmodified by high-frequency stimulation. Finally, collision techniques demonstrated antidromic conduction of impulses in the facial nerve from supraorbital to zygomatic points. Therefore, these “R1-like” responses are not the early component of a functionally recovered blink reflex but motor axon reflexes or ephaptic responses similar to the short latency responses observed following facial nerve regeneration or from sutured nerves in human forearms. © 1996 John Wiley & Sons, Inc.     

Contralateral reinnervation in Bell's palsy. A case report.

Congenital lesion of the left facial nerve trunk has been investigated in a 30-year-old woman. Upon stimulation of the left facial nerve, no response was evoked in any of the mimic muscles. The patient was able to perform voluntary contractions of the left corrugator glabellae muscle and of the left corner of the orbicular oral muscle; these contractions were recorded electromyographically. The stimulation of the right facial nerve elicited responses in the referred left mimic muscles. This circumstance indicated their activity to be due to contralateral reinnervation by the intact facial nerve. The blink reflex examination evoked no response on the left side, while the blinik reflex on the right side was elicited with both its components, both upon ipsi- and contralateral stimulation.