The hyperekplexias and their relationship to the normal startle reflex

The blink reflex and its modulation - Part 1: Physiological mechanisms

The blink reflex (BR) is a protective eye-closure reflex mediated by brainstem circuits. The BR is usually evoked by electrical supraorbital nerve stimulation but can be elicited by a variety of sensory modalities. It has a long history in clinical neurophysiology practice. Less is known, however, about the many ways to modulate the BR. Various neurophysiological techniques can be applied to examine different aspects of afferent and efferent BR modulation. In this line, classical conditioning, prepulse and paired-pulse stimulation, and BR elicitation by self-stimulation may serve to investigate various aspects of brainstem connectivity. The BR may be used as a tool to quantify top-down modulation based on implicit assessment of the value of blinking in a given situation, e.g., depending on changes in stimulus location and probability of occurrence. Understanding the role of non-nociceptive and nociceptive fibers in eliciting a BR is important to get insight into the underlying neural circuitry. Finally, the use of BRs and other brainstem reflexes under general anesthesia may help to advance our knowledge of the brainstem in areas not amenable in awake intact humans. This review summarizes talks held by the Brainstem Special Interest Group of the International Federation of Clinical Neurophysiology at the International Congress of Clinical Neurophysiology 2022 in Geneva, Switzerland, and provides a state-of-the-art overview of the physiology of BR modulation. Understanding the principles of BR modulation is fundamental for a valid and thoughtful clinical application (reviewed in part 2) (Gunduz et al., submitted).

Long Latency Reflexes in Clinical Neurology: A Systematic Review

BACKGROUND

Long latency reflexes (LLRs) are impaired in a wide array of clinical conditions. We aimed to illustrate the clinical applications and recent advances of LLR in various neurological disorders from a systematic review of published literature.

METHODS

We reviewed the literature using appropriately chosen MeSH terms on the database platforms of MEDLINE, Web of Sciences, and Google Scholar for all the articles from 1st January 1975 to 2nd February 2021 using the search terms "long loop reflex", "long latency reflex" and "C-reflex". The included articles were analyzed and reported using synthesis without meta-analysis (SWiM) guidelines.

RESULTS

Based on our selection criteria, 40 articles were selected for the systematic review. The various diseases included parkinsonian syndromes (11 studies, 217 patients), Huntington's disease (10 studies, 209 patients), myoclonus of varied etiologies (13 studies, 127 patients) including progressive myoclonic epilepsy (5 studies, 63 patients) and multiple sclerosis (6 studies, 200 patients). Patients with parkinsonian syndromes showed large amplitude LLR II response. Enlarged LLR II was also found in myoclonus of various etiologies. LLR II response was delayed or absent in Huntington's disease. Delayed LLR II response was present in multiple sclerosis. Among the other diseases, LLR response varied according to the location of cerebellar lesions while the results were equivocal in patients with essential tremor.

CONCLUSIONS

Abnormal LLR is observed in many neurological disorders. However, larger systematic studies are required in many neurological disorders in order to establish its role in diagnosis and management.

A review of the neural basis underlying the acoustic startle response with a focus on recent developments in mammals

The startle response consists of whole-body muscle contractions, eye-blink, accelerated heart rate, and freezing in response to a strong, sudden stimulus. It is evolutionarily preserved and can be observed in any animal that can perceive sensory signals, indicating the important protective function of startle. Startle response measurements and its alterations have become a valuable tool for exploring sensorimotor processes and sensory gating, especially in the context of pathologies of psychiatric disorders. The last reviews on the neural substrates underlying acoustic startle were published around 20 years ago. Advancements in methods and techniques have since allowed new insights into acoustic startle mechanisms. This review is focused on the neural circuitry that drives the primary acoustic startle response in mammals. However, there have also been very successful efforts to identify the acoustic startle pathway in other vertebrates and invertebrates in the past decades, so at the end we briefly summarize these studies and comment on the similarities and differences between species.

Myoclonus and other jerky movement disorders

Myoclonus and other jerky movements form a large heterogeneous group of disorders. Clinical neurophysiology studies can have an important contribution to support diagnosis but also to gain insight in the pathophysiology of different kind of jerks. This review focuses on myoclonus, tics, startle disorders, restless legs syndrome, and periodic leg movements during sleep. Myoclonus is defined as brief, shock-like movements, and subtypes can be classified based the anatomical origin. Both the clinical phenotype and the neurophysiological tests support this classification: cortical, cortical-subcortical, subcortical/non-segmental, segmental, peripheral, and functional jerks. The most important techniques used are polymyography and the combination of electromyography-electroencephalography focused on jerk-locked back-averaging, cortico-muscular coherence, and the Bereitschaftspotential. Clinically, the differential diagnosis of myoclonus includes tics, and this diagnosis is mainly based on the history with premonitory urges and the ability to suppress the tic. Electrophysiological tests are mainly applied in a research setting and include the Bereitschaftspotential, local field potentials, transcranial magnetic stimulation, and pre-pulse inhibition. Jerks due to a startling stimulus form the group of startle syndromes. This group includes disorders with an exaggerated startle reflex, such as hyperekplexia and stiff person syndrome, but also neuropsychiatric and stimulus-induced disorders. For these disorders polymyography combined with a startling stimulus can be useful to determine the pattern of muscle activation and thus the diagnosis. Assessment of symptoms in restless legs syndrome and periodic leg movements during sleep can be performed with different validated scoring criteria with the help of electromyography.

A Systematic Review of Fall Risk Factors in Stroke Survivors: Towards Improved Assessment Platforms and Protocols

Background/Purpose: To prevent falling, a common incident with debilitating health consequences among stroke survivors, it is important to identify significant fall risk factors (FRFs) towards developing and implementing predictive and preventive strategies and guidelines. This review provides a systematic approach for identifying the relevant FRFs and shedding light on future directions of research. Methods: A systematic search was conducted in 5 popular research databases. Studies investigating the FRFs in the stroke community were evaluated to identify the commonality and trend of FRFs in the relevant literature. Results: twenty-seven relevant articles were reviewed and analyzed spanning the years 1995-2020. The results confirmed that the most common FRFs were age (21/27, i.e., considered in 21 out of 27 studies), gender (21/27), motion-related measures (19/27), motor function/impairment (17/27), balance-related measures (16/27), and cognitive impairment (11/27). Among these factors, motion-related measures had the highest rate of significance (i.e., 84% or 16/19). Due to the high commonality of balance/motion-related measures, we further analyzed these factors. We identified a trend reflecting that subjective tools are increasingly being replaced by simple objective measures (e.g., 10-m walk), and most recently by quantitative measures based on detailed motion analysis. Conclusion: There remains a gap for a standardized systematic approach for selecting relevant FRFs in stroke fall risk literature. This study provides an evidence-based methodology to identify the relevant risk factors, as well as their commonalities and trends. Three significant areas for future research on post stroke fall risk assessment have been identified: 1) further exploration the efficacy of quantitative detailed motion analysis; 2) implementation of inertial measurement units as a cost-effective and accessible tool in clinics and beyond; and 3) investigation of the capability of cognitive-motor dual-task paradigms and their association with FRFs.

Central nervous system physiology

This is the second chapter of the series on the use of clinical neurophysiology for the study of movement disorders. It focusses on methods that can be used to probe neural circuits in brain and spinal cord. These include use of spinal and supraspinal reflexes to probe the integrity of transmission in specific pathways; transcranial methods of brain stimulation such as transcranial magnetic stimulation and transcranial direct current stimulation, which activate or modulate (respectively) the activity of populations of central neurones; EEG methods, both in conjunction with brain stimulation or with behavioural measures that record the activity of populations of central neurones; and pure behavioural measures that allow us to build conceptual models of motor control. The methods are discussed mainly in relation to work on healthy individuals. Later chapters will focus specifically on changes caused by pathology.

Myoclonus- A Review

Myoclonus is a hyperkinetic movement disorder characterized by a sudden, brief, involuntary jerk. Positive myoclonus is caused by abrupt muscle contractions, while negative myoclonus by sudden cessation of ongoing muscular contractions. Myoclonus can be classified in various ways according to body distribution, relation to activity, neurophysiology, and etiology. The neurophysiological classification of myoclonus by means of electrophysiological tests is helpful in guiding the best therapeutic strategy. Given the diverse etiologies of myoclonus, a thorough history and detailed physical examination are key to the evaluation of myoclonus. These along with basic laboratory testing and neurophysiological studies help in narrowing down the clinical possibilities. Though symptomatic treatment is required in the majority of cases, treatment of the underlying etiology should be the primary aim whenever possible. Symptomatic treatment is often not satisfactory, and a combination of different drugs is often required to control the myoclonus. This review addresses the etiology, classification, clinical approach, and management of myoclonus.

Progressive encephalomyelitis with rigidity and myoclonus (PERM)

Progressive encephalomyelitis with rigidity and myoclonus (PERM) is a subtype of stiff-person syndrome (formerly stiff-man syndrome). It is rare and disabling, and characterised by brainstem symptoms, muscle stiffness, breathing issues and autonomic dysfunction. We describe a 65-year-old man who presented with odynophagia together with tongue and neck swelling, followed by multiple cranial nerve palsies culminating in bilateral vocal cord paralysis with acute stridor. He subsequently developed progressive generalised hypertonia and painful limb spasms. Serum antiglycine receptor antibody was strongly positive, but antiglutamic acid decarboxylase and other antibodies relating to stiff-person syndrome were negative. We diagnosed PERM and gave intravenous corticosteroids and immunoglobulins without benefit; however, following plasma exchange he has made a sustained improvement.

Rescue of two trafficking-defective variants of the neuronal glycine transporter GlyT2 associated to hyperekplexia

Hyperekplexia is a rare sensorimotor syndrome characterized by pathological startle reflex in response to unexpected trivial stimuli for which there is no specific treatment. Neonates suffer from hypertonia and are at high risk of sudden death due to apnea episodes. Mutations in the human SLC6A5 gene encoding the neuronal glycine transporter GlyT2 may disrupt the inhibitory glycinergic neurotransmission and cause a presynaptic form of the disease. The phenotype of missense mutations giving rise to protein misfolding but maintaining residual activity could be rescued by facilitating folding or intracellular trafficking. In this report, we characterized the trafficking properties of two mutants associated with hyperekplexia (A277T and Y707C, rat numbering). Transporter molecules were partially retained in the endoplasmic reticulum showing increased interaction with the endoplasmic reticulum chaperone calnexin. One transporter variant had export difficulties and increased ubiquitination levels, suggestive of enhanced endoplasmic reticulum-associated degradation. However, the two mutant transporters were amenable to correction by calnexin overexpression. Within the search for compounds capable of rescuing mutant phenotypes, we found that the arachidonic acid derivative N-arachidonoyl glycine can rescue the trafficking defects of the two variants in heterologous cells and rat brain cortical neurons. N-arachidonoyl glycine improves the endoplasmic reticulum output by reducing the interaction transporter/calnexin, increasing membrane expression and improving transport activity in a comparable way as the well-established chemical chaperone 4-phenyl-butyrate. This work identifies N-arachidonoyl glycine as a promising compound with potential for hyperekplexia therapy.

GLYT1 encephalopathy: Further delineation of disease phenotype and discussion of pathophysiological mechanisms

GLYT1 encephalopathy is a form of glycine encephalopathy caused by disturbance of glycine transport. The phenotypic spectrum of the disease has not yet been completely described, as only four unrelated families with the disorder have been reported to date. Common features of affected patients include neonatal hypotonia, respiratory failure, encephalopathy, myoclonic jerks, dysmorphic features, and musculoeskeletal anomalies. All reported affected patients harbor biallelic genetic variants in SLC6A9. SNP array together with Sanger sequencing were performed in a newborn with arthrogryposis and severe neurological impairment. The novel genetic variant c.997delC in SLC6A9 was detected in homozygous state in the patient. At protein level, the predicted change is p.(Arg333Alafs*3), which most probably results in a loss of protein function. The variant cosegregated with the disease in the family. A subsequent pregnancy with ultrasound anomalies was also affected. The proband presented the core phenotypic features of GLYT1 encephalopathy, but also a burst suppression pattern on the electroencephalogram, a clinical feature not previously associated with the disorder. Our results suggest that the appearance of this pattern correlates with higher cerebrospinal fluid glycine levels and cerebrospinal fluid/plasma glycine ratios. A detailed discussion on the possible pathophysiological mechanisms of the disorder is also provided.

Dynamic acoustic salience evokes motor responses

Audio-motor integration is currently viewed as a predictive process in which the brain simulates upcoming sounds based on voluntary actions. This perspective does not consider how our auditory environment may trigger involuntary action in the absence of prediction. We address this issue by examining the relationship between acoustic salience and involuntary motor responses. We investigate how acoustic features in music contribute to the perception of salience, and whether those features trigger involuntary peripheral motor responses. Participants with little-to-no musical training listened to musical excerpts once while remaining still during the recording of their muscle activity with surface electromyography (sEMG), and again while they continuously rated perceived salience within the music using a slider. We show cross-correlations between 1) salience ratings and acoustic features, 2) acoustic features and spontaneous muscle activity, and 3) salience ratings and spontaneous muscle activity. Amplitude, intensity, and spectral centroid were perceived as the most salient features in music, and fluctuations in these features evoked involuntary peripheral muscle responses. Our results suggest an involuntary mechanism for audio-motor integration, which may rely on brainstem-spinal or brainstem-cerebellar-spinal pathways. Based on these results, we argue that a new framework is needed to explain the full range of human sensorimotor capabilities. This goal can be achieved by considering how predictive and reactive audio-motor integration mechanisms could operate independently or interactively to optimize human behavior.

Comparison of Muscle MEPs From Transcranial Magnetic and Electrical Stimulation and Appearance of Reflexes in Horses

Introduction

Transcranial electrical (TES) and magnetic stimulation (TMS) are both used for assessment of the motor function of the spinal cord in horses. Muscular motor evoked potentials (mMEP) were compared intra-individually for both techniques in five healthy horses. mMEPs were measured twice at increasing stimulation intensity steps over the extensor carpi radialis (ECR), tibialis cranialis (TC), and caninus muscles. Significance was set at p < 0.05. To support the hypothesis that both techniques induce extracranially elicited mMEPs, literature was also reviewed.

Results

Both techniques show the presence of late mMEPs below the transcranial threshold appearing as extracranially elicited startle responses. The occurrence of these late mMEPs is especially important for interpretation of TMS tracings when coil misalignment can have an additional influence. Mean transcranial motor latency times (MLT; synaptic delays included) and conduction velocities (CV) of the ECR and TC were significantly different between both techniques: respectively, 4.2 and 5.5 ms (MLT _{TMS -}-MLT _TES ), and -7.7 and -9.9 m/s (CV _TMS -CV _TES ). TMS and TES show intensity-dependent latency decreases of, respectively, -2.6 (ECR) and -2.7 ms (TC)/30% magnetic intensity and -2.6 (ECR) and -3.2 (TC) ms/30V. When compared to TMS, TES shows the lowest coefficients of variation and highest reproducibility and accuracy for MLTs. This is ascribed to the fact that TES activates a lower number of cascaded interneurons, allows for multipulse stimulation, has an absence of coil repositioning errors, and has less sensitivity for varying degrees of background muscle tonus. Real axonal conduction times and conduction velocities are most closely approximated by TES.

Conclusion

Both intracranial and extracranial mMEPs inevitably carry characteristics of brainstem reflexes. To avoid false interpretations, transcranial mMEPs can be identified by a stepwise latency shortening of 15-20 ms when exceeding the transcranial motor threshold at increasing stimulation intensities. A ring block around the vertex is advised to reduce interference by extracranial mMEPs. mMEPs reflect the functional integrity of the route along the brainstem nuclei, extrapyramidal motor tracts, propriospinal neurons, and motoneurons. The corticospinal tract appears subordinate in horses. TMS and TES are interchangeable for assessing the functional integrity of motor functions of the spinal cord. However, TES reveals significantly shorter MLTs, higher conduction velocities, and better reproducibility.

Hyperekplexia and other startle syndromes

Abnormal startle syndromes are classified into hyperekplexia, stimulus-induced, and neuropsychiatric startle syndromes. Hyperekplexia is attributed to a genetic, idiopathic, or symptomatic cause. Hereditary hyperekplexia is a treatable neurogenetic disorder. In patients with a hyperactive startle response, the first step is to characterize the extent and associations of 'response.' Secondary or symptomatic causes are particularly important in children, as they provide useful clinical clues to an underlying neurodevelopmental or neurodegenerative disorders. Particular attention should be given to any neonate or infant with generalized or episodic stiffness, drug-refractory seizures, recurrent apnea, stimulus-sensitive behavioral states, or sudden infant death syndrome. Eliciting a non-habituating head-retraction reflex to repeated nose tapping should be a part of routine examination of all new-borns. Vigevano maneuver should be taught to all families and health-care workers as an emergency rescue measure. The onset of excessive startle after infancy should direct investigations for an acquired cause such as brainstem injury, antibodies against glycine receptors, and neurodegeneration. Finally, one should not forget to evaluate unexplained cases of abnormal gait and frequent falls in adults for underlying undiagnosed startle syndromes. Oral clonazepam is an effective therapy besides behavioral and safety interventions for hereditary cases. The outcomes in genetic cases are good overall.

Myoclonus: An Electrophysiological Diagnosis

Background

Many different movement disorders have similar "jerk-like" phenomenology and can be misconstrued as myoclonus. Different types of myoclonus also share similar phenomenological characteristics that can be difficult to distinguish solely based on clinical exam. However, they have distinctive physiologic characteristics that can help refine categorization of jerk-like movements.

Objectives

In this review, we briefly summarize the clinical, physiologic, and pathophysiologic characteristics of different types of myoclonus. The methodology and technical considerations for the electrophysiologic assessment of jerk-like movements are reviewed. A simplistic pragmatic approach for the classification of myoclonus and other jerk-like movements based on objective electrophysiologic characteristics is proposed.

Conclusions

Clinical neurophysiology is an underutilized tool in the diagnosis and treatment of movement disorders. Various jerk-like movements have distinguishing physiologic characteristics, differentiated in the milliseconds range, which is beyond human capacity. We argue that the categorization of movement disorders as myoclonus can be refined based on objective physiology that can have important prognostic and therapeutic implications.

Top of Basilar Syndrome Presenting With Hyperekplexia Initially Diagnosed as a Convulsive Status Epilepticus

BACKGROUND

Hyperekplexia is a rare neurologic disorder characterized by pronounced startle responses to tactile or acoustic stimuli and increase tone. Acquired hyperekplexia is usually seen in brainstem pathologies and when it develops acutely it can be easily misdiagnosed as a convulsive seizure.

CASE REPORT

A 38-year-old man presented with acute onset generalized brief involuntary jerky movements and a decreased level of consciousness. He was initially diagnosed with convulsive status epilepticus for which he received multiple antiseizure medications without any improvement. Further investigations revealed abnormal oculocephalic reflex response and that his movements were in fact hyperkeplexia caused by brainstem infarction with basilar artery thrombus secondary to right vertebral artery dissection. Emergent thrombectomy was performed and he was eventually discharged to a rehabilitation facility. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Emergency physicians should be aware of hyperekplexia and how to differentiate it from convulsive stats epilepticus because the pathology and the emergent treatment of these 2 serious conditions are different. An underlying acquired brainstem pathology (especially basilar artery thromboembolism) should be suspected in any patient with untypical convulsive like movements along with focal neurologic signs compatible with brain stem pathology even when computed tomography imaging is normal. © 2020 Elsevier Inc.

Principles of Electrophysiological Assessments for Movement Disorders

Electrophysiological studies can provide objective and quantifiable assessments of movement disorders. They are useful in the diagnosis of hyperkinetic movement disorders, particularly tremors and myoclonus. The most commonly used measures are surface electromyography (sEMG), electroencephalography (EEG) and accelerometry. Frequency and coherence analyses of sEMG signals may reveal the nature of tremors and the source of the tremors. The effects of voluntary tapping, ballistic movements and weighting of the limbs can help to distinguish between organic and functional tremors. The presence of Bereitschafts-potentials and beta-band desynchronization recorded by EEG before movement onset provide strong evidence for functional movement disorders. EMG burst durations, distributions and muscle recruitment orders may identify and classify myoclonus to cortical, subcortical or spinal origins and help in the diagnosis of functional myoclonus. Organic and functional cervical dystonia can potentially be distinguished by EMG power spectral analysis. Several reflex circuits, such as the long latency reflex, blink reflex and startle reflex, can be elicited with different types of external stimuli and are useful in the assessment of myoclonus, excessive startle and stiff person syndrome. However, limitations of the tests should be recognized, and the results should be interpreted together with clinical observations.

Spontaneous, Voluntary, and Reflex Blinking in Clinical Practice

Blinking is one of the motor acts performed more frequently by healthy human subjects. It involves the reciprocal action of at least two muscles: the orbicularis oculi shows a brief phasic activation while the levator palpebrae shows transient inhibition. In clinical practice, noninvasive recording of the orbicularis oculi activity is sufficient to obtain useful information for electrodiagnostic testing. Blinking can be spontaneous, voluntary, or reflex. Although the analysis of spontaneous blinks can already furnish interesting data, most studies are based on reflex blinking. This article is a review of some of the alterations that can be observed in blinking, focusing in four patterns of abnormality that can be distinguished in the blink reflex: (1) afferent versus efferent, which allows characterization of trigeminal or facial lesions; (2) peripheral versus central, which distinguishes alterations in nerve conduction from those involving synaptic delay; (3) upper versus lower brainstem lesions, which indicates the lesions involving specific circuits for trigeminal and somatosensory blink reflexes; and (4) asymmetric abnormal excitability pattern, which shows a unilateral alteration in the descending control of excitability in brainstem circuits. The blink reflex excitability recovery curve to paired stimuli may provide information about other modulatory inputs to trigemino-facial circuits, such as those proposed for the connection between basal ganglia and trigeminal neurons. Finally, prepulse inhibition of blink reflex reflects the motor surrogate of subcortical gating on sensory volleys, which is still another window by which electrodiagnosis can document motor control mechanisms and their abnormalities in neurologic diseases.

Aging changes in protective balance and startle responses to sudden drop perturbations

This study investigated aging changes in protective balance and startle responses to sudden drop perturbations and their effect on landing impact forces (vertical ground reaction forces, vGRF) and balance stability. Twelve healthy older (6 men; mean age = 72.5 ± 2.32 yr, mean ± SE) and 12 younger adults (7 men; mean age = 28.09 ± 1.03 yr) stood atop a moveable platform and received externally triggered drop perturbations of the support surface. Electromyographic activity was recorded bilaterally over the sternocleidomastoid (SCM), middle deltoid, biceps brachii, vastus lateralis (VL), biceps femoris (BF), medial gastrocnemius (MG), and tibialis anterior (TA). Whole body kinematics were recorded with motion analysis. Stability in the anteroposterior direction was quantified using the margin of stability (MoS). Incidence of early onset of bilateral SCM activation within 120 ms after drop onset was present during the first-trial response (FTR) for all participants. Co-contraction indexes during FTRs between VL and BF as well as TA and MG were significantly greater in the older group (VL/BF by 26%, P < 0.05; TA/MG by 37%, P < 0.05). Reduced shoulder abduction between FTR and last-trial responses, indicative of habituation, was present across both groups. Significant age-related differences in landing strategy were present between groups, because older adults had greater trunk flexion (P < 0.05) and less knee flexion (P < 0.05) that resulted in greater peak vGRFs and decreased MoS compared with younger adults. These findings suggest age-associated abnormalities of delayed, exaggerated, and poorly habituated startle/postural FTRs are linked with greater landing impact force and diminished balance stabilization. NEW & NOTEWORTHY This study investigated the role of startle as a pathophysiological mechanism contributing to balance impairment in aging. We measured neuromotor responses as younger and older adults stood on a platform that dropped unexpectedly. Group differences in landing strategies indicated age-associated abnormalities of delayed, exaggerated, and poorly habituated startle/postural responses linked with a higher magnitude of impact force and decreased balance stabilization. The findings have implications for determining mechanisms contributing to falls and related injuries.

Aging effects of motor prediction on protective balance and startle responses to sudden drop perturbations

This pilot study investigated the effect of age on the ability of motor prediction during self-triggered drop perturbations (SLF) to modulate startle-like first trial response (FTR) magnitude during externally-triggered (EXT) drop perturbations. Ten healthy older (71.4 ± 1.44 years) and younger adults (26.2 ± 1.63 years) stood atop a moveable platform and received blocks of twelve consecutive EXT and SLF drop perturbations. Following the last SLF trial, participants received an additional EXT trial spaced 20 min apart to assess retention (EXT RTN) of any modulation effects. Electromyographic (EMG) activity was recorded bilaterally over the sternocleidomastoid (SCM), vastus lateralis (VL), biceps femoris (BF), medial gastrocnemius (MG), and tibialis anterior (TA). Whole-body kinematics and kinetic data were recorded. Stability in the antero-posterior direction was quantified using the margin of stability (MoS). Compared with EXT trials, both groups reduced SCM peak amplitude responses during SLF and EXT RTN trials. VL/BF and TA/MG coactivation were reduced during SLF FTR compared to EXT FTR (p < 0.05) with reduced peak vertical ground reaction forces (vGRF) in both younger and older adults (p < 0.05). Older adults increased their MoS during SLF FTR compared to EXT FTR (p < 0.05). Both groups performed more eccentric work during SLF trials compared to EXT (p < 0.05). These findings indicate that abnormal startle effects with aging may interfere with balance recovery and increase risk of injury with external balance perturbations. Motor prediction may be used to acutely mitigate abnormal startle/postural responses with aging.

Brainstem lesions and gait

The brainstem contains virtually all of the important structures involved in experimental models of locomotion, encompassing control of upright posture, balance, and stepping. The physiologic basis for these functions is intricately related. Studies of the effects of lesions and disease on these functions in humans are limited to clinical observation and hampered by the anatomic complexity of closely spaced structures and lack of selectivity of lesions. Accordingly, any description of the clinical effects of brainstem lesions on gait and posture is imprecise because weakness and ataxia either predominate over or obscure any selective disturbance of the control of locomotion that may be correlated with the findings in experimental models. New and more sophisticated methods of brain imaging along with physiologic studies of balance and stepping may provide advances in human gait disorders, especially in relation to the brainstem control of locomotion.

A novel exaggerated "spino-bulbo-spinal like" reflex of lower brainstem origin

BACKGROUND

Many different oligosynaptic reflexes are known to originate in the lower brainstem which share phenomenological and neurophysiological similarities.

OBJECTIVE

To evaluate and discuss the differences and aberrancies among these reflexes, which are hard to discern clinically using neurophysiological investigations with the help of a case report.

METHODS

We describe the clinical and neurophysiological assessment of a young man who had a childhood history of opsoclonus-myoclonus syndrome with residual mild ataxia and myoclonic jerks in the distal extremities presenting with subacute onset total body jerks sensitive to sound and touch (in a limited dermatomal distribution), refractory to medications.

RESULTS

Based on clinical characteristics and insights gained from neurophysiological testing we could identify a novel reflex of caudal brainstem origin.

CONCLUSIONS

The reflex described is likely an exaggerated normal reflex, likely triggered by a dolichoectatic vertebral arterial compression and shares characteristics of different reflexes known to originate in caudal brainstem, which subserve distinctive roles in human postural control.

Electrophysiologic testing aids diagnosis and subtyping of myoclonus

OBJECTIVE

To determine the contribution of electrophysiologic testing in the diagnosis and anatomical classification of myoclonus.

METHODS

Participants with a clinical diagnosis of myoclonus were prospectively recruited, each undergoing a videotaped clinical examination and battery of electrophysiologic tests. The diagnosis of myoclonus and its subtype was reviewed after 6 months in the context of the electrophysiologic findings and specialist review of the videotaped clinical examination.

RESULTS

Seventy-two patients with myoclonus were recruited. Initial clinical anatomical classification included 25 patients with cortical myoclonus, 7 with subcortical myoclonus, 2 with spinal myoclonus, and 15 with functional myoclonic jerks. In 23 cases, clinical anatomical classification was not possible because of the complexity of the movement disorder. Electrophysiologic testing was completed in 66, with agreement of myoclonus in 60 (91%) and its subtype in 28 (47%) cases. Subsequent clinical review by a movement disorder specialist agreed with the electrophysiologic findings in 52 of 60; in the remaining 8, electrophysiologic testing was inconclusive.

CONCLUSIONS

Electrophysiologic testing is an important additional tool in the diagnosis and anatomical classification of myoclonus, also aiding in decision-making regarding therapeutic management. Further development of testing criteria is necessary to optimize its use in clinical practice.

[Myoclonus as a movement disorder]

Myoclonus is often a diagnostic and therapeutic challenge due to its broad phenomenological variability and limited therapeutic options. This article gives a short survey and characterizes in detail two common types of myoclonus, cortical myoclonus and reticular reflex myoclonus. Clinical testing and electrophysiological investigations provide relevant local diagnostic indications for the generating structure(s). Such indications would influence not only the strategies of neuroimaging and laboratory investigations aimed at clarifying the underlying cause but also the selection of drugs to suppress myoclonus.

A case of Bickerstaff brainstem encephalitis with transient reflex myoclonus

A 33-year-old woman was admitted due to disturbance of consciousness, dysarthria, dysphagia, sensory disturbances and weakness of the left upper limb after mycoplasma infection. She was treated with intravenous immunoglobulin and intravenous high-dose methylprednisolone as Bickerstaff brainstem encephalitis (BBE). On the 15th hospital day, reflex myoclonus appeared on her face, neck, body and limbs induced by techniques of jaw jerk reflex and patellar tendon reflex. The myoclonus was disappeared after two weeks in accordance with improvement of BBE. The transient reflex myoclonus may be originated from brainstem lesion which was affected by BBE. Reflex myoclonus is thought to be rare symptom in patient with BBE.

Non-invasive, multimodal analysis of cortical activity, blood volume and neurovascular coupling in infantile spasms using EEG-fNIRS monitoring

Although infantile spasms can be caused by a variety of etiologies, the clinical features are stereotypical. The neuronal and vascular mechanisms that contribute to the emergence of infantile spasms are not well understood. We performed a multimodal study by simultaneously recording electroencephalogram and functional Near-infrared spectroscopy in an intentionally heterogeneous population of six children with spasms in clusters. Regardless of the etiology, spasms were accompanied by two phases of hemodynamic changes; an initial change in the cerebral blood volume (simultaneously with each spasm) followed by a neurovascular coupling in all children except for the one with a large porencephalic cyst. Changes in cerebral blood volume, like the neurovascular coupling, occurred over frontal areas in all patients regardless of any brain damage suggesting a diffuse hemodynamic cortical response. The simultaneous motor activation and changes in cerebral blood volume might result from the involvement of the brainstem. The inconstant neurovascular coupling phase suggests a diffuse activation of the brain likely resulting too from the brainstem involvement that might trigger diffuse changes in cortical excitability.

Sporadic hyperekplexia due to self-limiting brainstem encephalopathy

Hyperekplexia is a rare movement disorder characterized by pathologically exaggerated response to unexpected stimuli. It is differentiated from the normal startle reflex by its lower threshold, higher intensity, and resistance to habituation. Many of the acquired hyperekplexias result from brainstem involvement such as encephalitis, infarct, hemorrhage, pontocerebellar hypoplasia and medullary compression. This case report depicts a rare manifestation of hyperekplexia. The unusual aspect of this case was the vocalization that was reproduced in response to startling stimuli. Startle induced vocalization is not a part of the classical hyperekplexia description. When faced with a patient with pathologically exaggerated response to unexpected stimuli, the physician should consider this rare condition in the differential diagnosis, and also keep in mind that the disease may present with features different from those listed in the textbooks.

Synaptopathies: synaptic dysfunction in neurological disorders - A review from students to students

Synapses are essential components of neurons and allow information to travel coordinately throughout the nervous system to adjust behavior to environmental stimuli and to control body functions, memories, and emotions. Thus, optimal synaptic communication is required for proper brain physiology, and slight perturbations of synapse function can lead to brain disorders. In fact, increasing evidence has demonstrated the relevance of synapse dysfunction as a major determinant of many neurological diseases. This notion has led to the concept of synaptopathies as brain diseases with synapse defects as shared pathogenic features. In this review, which was initiated at the 13th International Society for Neurochemistry Advanced School, we discuss basic concepts of synapse structure and function, and provide a critical view of how aberrant synapse physiology may contribute to neurodevelopmental disorders (autism, Down syndrome, startle disease, and epilepsy) as well as neurodegenerative disorders (Alzheimer and Parkinson disease). We finally discuss the appropriateness and potential implications of gathering synapse diseases under a single term. Understanding common causes and intrinsic differences in disease-associated synaptic dysfunction could offer novel clues toward synapse-based therapeutic intervention for neurological and neuropsychiatric disorders. In this Review, which was initiated at the 13th International Society for Neurochemistry (ISN) Advanced School, we discuss basic concepts of synapse structure and function, and provide a critical view of how aberrant synapse physiology may contribute to neurodevelopmental (autism, Down syndrome, startle disease, and epilepsy) as well as neurodegenerative disorders (Alzheimer's and Parkinson's diseases), gathered together under the term of synaptopathies. Read the Editorial Highlight for this article on page 783.

Sex-Specific Automatic Responses to Infant Cries: TMS Reveals Greater Excitability in Females than Males in Motor Evoked Potentials

Neuroimaging reveals that infant cries activate parts of the premotor cortical system. To validate this effect in a more direct way, we used event-related transcranial magnetic stimulation (TMS). Here, we investigated the presence and the time course of modulation of motor cortex excitability in young adults who listened to infant cries. Specifically, we recorded motor evoked potentials (MEPs) from the biceps brachii (BB) and interosseus dorsalis primus (ID1) muscles as produced by TMS delivered from 0 to 250 ms after sound onset in six steps of 50 ms in 10 females and 10 males. We observed an excitatory modulation of MEPs at 100 ms from the onset of infant cry specific to females and to the ID1 muscle. We regard this modulation as a response to natural cry sounds because it was attenuated to stimuli increasingly different from natural cry and absent in a separate group of females who listened to non-cry stimuli physically matched to natural infant cries. Furthermore, the 100-ms latency of this response is not compatible with a voluntary reaction to the stimulus but suggests an automatic, bottom-up audiomotor association. The brains of adult females appear to be tuned to respond to infant cries with automatic motor excitation.

Autoimmune channelopathies in paraneoplastic neurological syndromes

Paraneoplastic neurological syndromes and autoimmune encephalitides are immune neurological disorders occurring or not in association with a cancer. They are thought to be due to an autoimmune reaction against neuronal antigens ectopically expressed by the underlying tumour or by cross-reaction with an unknown infectious agent. In some instances, paraneoplastic neurological syndromes and autoimmune encephalitides are related to an antibody-induced dysfunction of ion channels, a situation that can be labelled as autoimmune channelopathies. Such functional alterations of ion channels are caused by the specific fixation of an autoantibody upon its target, implying that autoimmune channelopathies are usually highly responsive to immuno-modulatory treatments. Over the recent years, numerous autoantibodies corresponding to various neurological syndromes have been discovered and their mechanisms of action partially deciphered. Autoantibodies in neurological autoimmune channelopathies may target either directly ion channels or proteins associated to ion channels and induce channel dysfunction by various mechanisms generally leading to the reduction of synaptic expression of the considered channel. The discovery of those mechanisms of action has provided insights on the regulation of the synaptic expression of the altered channels as well as the putative roles of some of their functional subdomains. Interestingly, patients' autoantibodies themselves can be used as specific tools in order to study the functions of ion channels. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Hyperekplexia: Treatment of a Severe Phenotype and Review of the Literature

Hyperekplexia is a rare disorder caused by autosomal dominant or recessive modes of inheritance and characterized by episodes of exaggerated startle. Five causative genes have been identified to date. The syndrome has been recognized for decades and due to its rarity, the literature contains mostly descriptive reports, many early studies lacking molecular genetic diagnoses. A spectrum of clinical severity exists. Severe cases can lead to neonatal cardiac arrest and death during an episode, an outcome prevented by early diagnosis and clinical vigilance. Large treatment studies are not feasible, so therapeutic measures continue to be empiric. A marked response to clonazepam is often reported but refractory cases exist. Herein we report the clinical course and treatment response of a severely affected infant homozygous for an SLC6A5 nonsense mutation and review the literature summarizing the history and genetic understanding of the disease as well as the described comorbidities and treatment options.

[Severe PERM syndrom mimicking tetanus]

We report the case of a 55-year-old man without significant medical history admitted to the ICU for a progressive paralysis mimicking life-threatening tetanus. Evolution with classical tetanus treatment was negative, with the need for ventilator support and worsening condition being life threatening. Uncommon evolution revealed a rare glycin antibody-associated hyperekplexia (progressive encephalomyelitis with rigidity syndrome). Patient dramatically improved with immunosuppressive therapy including plasmatic exchanges, cyclophasmid and high dose corticoid infusions. Intensivists should be aware of this very rare syndrome whose treatment is the opposite of tetanus while presentation is very close. Optimal and treatment could lead to prolonged survival.

Myoclonus

PURPOSE OF REVIEW

Myoclonus remains a challenging movement phenotype to characterize, evaluate, and treat. A systematic assessment of the temporal sequence, phenomenology, and distribution of movements can assist in the rational approach to diagnosis and management.

RECENT FINDINGS

Cortical forms of myoclonus are increasingly recognized as primarily cerebellar disorders. A syndrome of orthostatic myoclonus has been recognized by electrophysiology in patients with neurodegenerative disorders, mainly in Alzheimer disease, accounting for impairments in gait and balance previously mischaracterized as normal pressure hydrocephalus or orthostatic tremor. Tyrosine hydroxylase deficiency and Silver-Russell syndrome (uniparental disomy of chromosome 7) have been established as two novel causes of the myoclonus-dystonia syndrome. Mutations in the glycine receptor (GlyR) α1-subunit gene (GLRA1) explain the major expression of hyperekplexia, an inherited excessive startle disorder, butnewly identified mutations in GlyR β-subunit (GLRB) and glycine transporter 2 (GlyT2) genes (SLC6A5) account for "minor" forms of this disorder manifested as excessive startle and hypnic jerks. The entity previously known as palatal myoclonus has been reclassified as palatal tremor in recognition of its clinical and electromyographic features and no longer enters the differential diagnosis of myoclonic disorders. Increasing documentation of psychogenic features in patients previously characterized as having propriospinal myoclonus has cast doubts on the existence of this distinctive disorder.

SUMMARY

Myoclonus can be a prominent manifestation of a wide range of disorders. Electrophysiologic testing aids in distinguishing myoclonus from other mimics and classifying them according to cortical, subcortical, or spinal origin, which assists the choice of treatment. Despite the lack of randomized clinical trials, levetiracetam appears most effective in patients with cortical myoclonus, whereas clonazepam remains the only first-line therapeutic option in subcortical and spinal myoclonus.

Transient loss of consciousness and syncope

Syncope describes a sudden and brief transient loss of consciousness (TLOC) with postural failure due to cerebral global hypoperfusion. The term TLOC is used when the cause is either unrelated to cerebral hypoperfusion or is unknown. The most common causes of syncopal TLOC include: (1) cardiogenic syncope (cardiac arrhythmias, structural cardiac diseases, others); (2) orthostatic hypotension (due to drugs, hypovolemia, primary or secondary autonomic failure, others); (3) neurally mediated syncope (cardioinhibitory, vasodepressor, and mixed forms). Rarely neurologic disorders (such as epilepsy, transient ischemic attacks, and the subclavian steal syndrome) can lead to cerebal hypoperfusion and syncope. Nonsyncopal TLOC may be due to neurologic (epilepsy, sleep attacks, and other states with fluctuating vigilance), medical (hypoglycemia, drugs), psychiatric, or post-traumatic disorders. Basic diagnostic workup of TLOC includes a thorough history and physical examination, and a 12-lead electrocardiogram (ECG). Blood testing, electroencephalogram (EEG), magnetic resonance imaging (MRI) of the brain, echocardiography, head-up tilt test, carotid sinus massage, Holter monitoring, and loop recorders should be obtained only in specific contexts. Management strategies involve pharmacologic and nonpharmacologic interventions, and cardiac pacing.

[Case of post-anoxic reticular reflex myoclonus]

BACKGROUND

Reticular reflex myoclonus is a rare condition with only a few cases clearly documented on video. The purpose of this paper is to report a patient manifesting typical clinical picture documented on video and characteristic electrophysiological features of reticular reflex myoclonus.

CASE

A 60-year-old woman presented with spontaneous and stimulus-sensitive myoclonic jerks involving the face, neck and upper extremities following anoxic episode. The patient was investigated electrophysiologically. Surface electromyogram showed brief myoclonic activity starting from the sternocleidomastoid and spreading up to the orbicularis oculi as well as down to the upper limb muscles. Cortical somatosensory evoked potentials and long-latency reflex were not enhanced.

CONCLUSION

Clinical features and electrophysiological findings of this case are consistent with those of reticular reflex myoclonus originally reported by Hallett et al. in 1977.

Startle myoclonus induced by Lyme neuroborreliosis: a case report

Introduction

The normal startle response is a form of physiological myoclonus. Its anatomic origin is probably the brain stem. Pathologic startles are defined as reproducible exaggerated startle responses to trivial and not surprising stimuli. Symptomatic forms of an exaggerated startle response can be due to a variety of brain stem disorders. We have, however, found scant data about an exaggerated startle reflex induced by Lyme neuroborreliosis. We therefore report the case of a patient with this unusual presentation.

Case presentation

A 69-year old Caucasian man presented with a two-week history of a pronounced startle myoclonus, as well as a four-week history of double vision, gait disturbance and severe lancinating pain in his upper thoracic region. Neurological examination showed an excessive startle reaction of his upper trunk evoked by visual and tactile stimulation, a positive sign of Lhermitte, mild right-sided palsy of his sixth and seventh cranial nerve, moderate dysarthria, very brisk deep tendon reflexes, pallhypesthesia of his legs, and an atactic gait disturbance. A diagnosis of a Lyme neuroborreliosis was confirmed by cerebrospinal fluid examination. Under intravenous treatment with ceftriaxone, our patient improved considerably with complete remission in a follow-up at two months.

Conclusions

This case illustrates the chameleon role that neuroborreliosis likes to play: although the wide spectrum of different symptoms that neuroborreliosis can present with has been described, to the best of our knowledge this is the first case report about a symptomatic form of a pathologic startle response as the predominating sign of Lyme neuroborreliosis.

Clinical features and genetic analysis of children with hyperekplexia in Korea

Hyperekplexia is a rare inherited neurologic disorder that is characterized by hypertonia and an exaggerated startle response to sudden external stimuli. Until now, 5 genes are known to be associated with hyperekplexia: GLRA1, SLC6A5, GLRB, GPHN, and ARHGEF9. In this report, we performed a clinical and genetic analysis of 4 Korean children with hyperekplexia. Two patients had typical clinical manifestations of hyperekplexia that initially were misdiagnosed as epilepsy. Direct sequencing of the GLRB and GLRA1 genes revealed 2 novel mutations, GLRB c.298-1G>A and c.1028C>T (p.S343F), in patient 1 and 1 novel mutation, GLRA1 c.895C>T (p.R299X), in patient 2. The other 2 familial cases, patients 3 and 4, exhibited startle responses, which appeared at the age of 1 year, and had global developmental delay. Those patients showed negative results for the 5 genes.

White matter abnormalities in gene-positive myoclonus-dystonia

Myoclonus-dystonia is an autosomal dominantly inherited movement disorder clinically characterized by myoclonic jerks and dystonic movements of the upper body. Functional imaging and structural gray matter imaging studies in M-D suggest defective sensorimotor integration and an association between putaminal volume and severity of dystonia, possibly because of neuronal plasticity. As we expect changes in the connections between the cortical and subcortical regions, we performed a combination of white matter voxel-based morphometry (wVBM) and diffusion tensor imaging (DTI) to detect macro- and microstructural white matter changes, respectively, in DYT-11 mutations carriers (M-D). Sixteen clinically affected DYT-11 mutation carriers and 18 control subjects were scanned with 3-Tesla MRI to compare white matter volume, fractional anisotropy, and mean diffusivity between groups. In DYT11 mutation carriers, increased white matter volume and FA and decreased mean diffusivity were found in the subthalamic area of the brain stem, including the red nucleus. Furthermore, decreased mean diffusivity was found in the subgyral cortical sensorimotor areas. The white matter changes found in the subthalamic area of the brain stem, connecting the cerebellum with the thalamus, are compatible with the hypothesis that abnormal function in M-D involves a network that includes the cerebellum, brain stem, and basal ganglia. Whether these changes are causative or an effect of M-D requires further study.

Startle Stimuli Exert Opposite Effects on Human Cortical and Spinal Motor System Excitability in Leg Muscles

Increased excitability of the spinal motor system has been observed after loud and unexpected acoustic stimuli (AS) preceding H-reflexes. The paradigm has been proposed as an electrophysiological marker of reticulospinal tract activity in humans. The brainstem reticular formation also maintains dense anatomical interconnections with the cortical motor system. When a startling AS is delivered, prior to transcranial magnetic stimulation (TMS), the AS produces a suppression of motor evoked potential (MEP) amplitude in hand and arm muscles of healthy subjects. Here we analyzed the conditioning effect of a startling AS on MEP amplitude evoked by TMS to the primary motor leg area. Ten healthy volunteers participated in two experiments that used a conditioning-test paradigm. In the first experiment, a startling AS preceded a suprathreshold transcranial test stimulus. The interstimulus interval (ISI) varied between 20 to 160 ms. When given alone, the test stimulus evoked a MEP amplitude of approximately 0.5 mV in the slightly preinervated soleus muscle (SOL). In the second experiment, the startling AS was used to condition the size of the H-reflex in SOL muscle. Mean MEP amplitude was calculated for each ISI. The conditioning AS suppressed MEP amplitude at ISIs of 30-80 ms. By contrast, H-reflex amplitude was augmented at ISIs of 100-200 ms. In conclusions, acoustic stimulation exerts opposite and ISI-specific effects on the amplitude of MEPs and H-reflex in the SOL muscle, indicating different mechanism of auditory-to-motor interactions at cortical and spinal level of motor system.

Milestones in myoclonus

This review examines some of the advances in understanding myoclonus over the last 25 years. The classification of myoclonus into cortical, brainstem, and spinal forms has been consolidated, each with distinctive clinical characteristics and physiological mechanisms. New genetic causes of myoclonus have been identified, and the molecular basis of several of these conditions has been discovered. It is increasingly apparent that disease of the cerebellum is particularly important in the genesis of cortical reflex myoclonus. However, the precise mechanism and origin of myoclonus in many situations remain uncertain. Effective treatment of myoclonus remains limited, and the challenge lies ahead to develop more therapeutic options.

Milestones in clinical neurophysiology

Over the last 25 years, clinical neurophysiology has made many advances in the understanding, diagnosis, and even treatment of different movement disorders. Transcranial magnetic stimulation has been the biggest technical advance. Progress in pathophysiology includes improved knowledge about bradykinesia in Parkinson's disease, loss of inhibition and increased plasticity in dystonia, abnormal startle in hyperekplexia, and various features of psychogenic movement disorders that can aid diagnosis. Studies have been done looking at the use of noninvasive brain stimulation for therapy, but effects are generally small.

The primate reticulospinal tract, hand function and functional recovery

Abstract

The primate reticulospinal tract is usually considered to control proximal and axial muscles, and to be involved mainly in gross movements such as locomotion, reaching and posture. This contrasts with the corticospinal tract, which is thought to be involved in fine control, particularly of independent finger movements. Recent data provide evidence that the reticulospinal tract can exert some influence over hand movements. Although clearly secondary to the corticospinal tract in healthy function, this could assume considerable importance after corticospinal lesion (such as following stroke), when reticulospinal systems could provide a substrate for some recovery of function. We need to understand more about the abilities of the reticular formation to process sensory input and guide motor output, so that rehabilitation strategies can be optimised to work with the innate capabilities of reticular motor control.