Neurophysiological classification of myoclonus

doi:10.1016/j.neucli.2006.11.004

Neurophysiologie Clinique/Clinical Neurophysiology

Volume 36, Issues 5–6, September–December 2006, Pages 267-269

https://doi.org/10.1016/j.neucli.2006.11.004 Get rights and content

Abstract

Myoclonus can be diagnosed and classified mainly based on clinical features. Neurophysiologic studies help confirm clinical diagnosis and classification, and understand underlying physiological mechanisms. The neurophysiologic classification of myoclonus is mainly based on surface EMG (individual EMG patterns, muscle spatial distribution and time sequence of muscle activation), EEG, EEG/EMG relationships (jerk-locked back-averaging, cortico-muscular coherence), somatosensory evoked potentials, and long-loop reflexes. Paired stimulation evoked response/long loop reflex and jerk-locked evoked responses evaluate the excitability changes of the primary somatosensory cortex. Transcranial magnetic stimulation can evaluate the excitability state of the primary motor cortex.

Résumé

La classification des myoclonies repose avant tout sur des arguments cliniques. L'examen neurophysiologique permet de confirmer le diagnostic clinique des myoclonies et d'en préciser les mécanismes physiologiques sous-jacents. La classification neurophysiologique des myoclonies repose principalement sur l'EMG de surface (aspect des réponses au niveau d'un muscle donné, relations spatiotemporelles au niveau d'un ensemble de muscles), l'EEG, les relations EEG/EMG (moyennage à rebours, étude de la cohérence corticomusculaire), les potentiels évoqués somesthésiques et les réflexes à longue boucle. L'utilisation de stimulations pairées permet de préciser l'excitabilité du cortex sensoriel. L'excitabilité du cortex moteur primaire peut être évaluée par la stimulation magnétique transcrânienne.

Introduction

Myoclonus can be diagnosed and classified mainly based on clinical features, namely into cortical, brainstem, spinal, and unclassified. Neurophysiological studies help confirming the clinical diagnosis as well as the classification, and understanding the underlying physiological mechanisms [1]. Myoclonus can be classified from various viewpoints depending on which physiological parameter is focused upon, and which physiological test is adopted. In other words, the most appropriate test has to be chosen to study each parameter.

Section snippets

Classification based on the electromyographic (EMG) correlates

Recording of muscle activities associated with myoclonus (EMG correlates of myoclonus) by using surface electrodes provides the most essential information on any kind of myoclonus.

Classification based on the electroencephalographic (EEG) correlates

Demonstration of EEG spikes or spike-and-waves in association with myoclonus usually suggests its cortical origin, but absence of EEG spikes in association with myoclonus does not entirely exclude the possibility of cortical origin. Myoclonus of hand is associated with EEG spike or spike-and-wave, which is localized to the hand area of the contralateral sensori-motor cortex (approximately at C3 or C4 of the International 10–20 System), and in case of foot myoclonus to the midline central region

Classification based on the jerk-locked back averaging

Back averaging of EEGs time-locked to the onset of myoclonus EMG discharges might disclose a cortical spike which may not be detected by the conventional EEG-EMG recording. However, failure of back averaging to demonstrate the spike does not necessarily means subcortical origin of the myoclonus, because back averaging of the simultaneously recorded magnetoencephalogram (MEG) sometimes detects the spike that is not detectable on EEG even by back averaging. This is due to the different

Classification based on the cortico-muscular coherence

As described above, cortical myoclonus is often composed of rhythmic oscillations of muscle discharges, and accompanied by rhythmic oscillations of EEG. In this case, demonstration of increased coherence between cortical and muscle activities for certain frequency bands suggests the important role of cortical driving in the myoclonus generation [4]. This technique is especially useful for the study of rhythmic cortical myoclonus, and in contrast with jerk-locked back averaging, it takes much

Classification based on sensory evoked responses and long-loop reflexes

Most patients with cortical myoclonus show extremely enhanced cortical components of somatosensory evoked potentials (SEPs). Demonstration of giant SEP suggests cortical origin of the myoclonus. When recording sensory evoked responses, it is worthwhile recording EMGs simultaneously from the extremity which is stimulated as well as from other extremities to record long-loop EMG reflexes. If an EMG discharge is evoked in the hand at 40–45 ms after the median nerve stimulation at wrist, or

Paired stimulation evoked response/long-loop reflex and jerk-locked evoked responses

These tests form a special test battery to evaluate the excitability change of the primary somatosensory cortex following the cortical response/C reflex to the initial impulse arrival in comparison with that following the spontaneous myoclonus [2]. In some cases of cortical reflex myoclonus, especially those manifesting rhythmic myoclonus, the increased excitability of the somatosensory cortex is demonstrated at a certain time after the first stimulus as well as the spontaneous myoclonus.

Transcranial magnetic stimulation (TMS)

This test is applied to study the change of motor cortex excitability following the impulse arrival due to external stimuli as well as following a spontaneous myoclonus. In contrast to the paired stimulation evoked response/long-loop reflex and jerk-locked evoked responses described above, TMS can evaluate the excitability state of the primary motor cortex directly [8].

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Pathogenesis of giant somatosensory evoked potentials in progressive myoclonic epilepsy
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Intrahemispheric and interhemispheric spread of cerebral cortical myoclonic activity and its relevance to epilepsy
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P. Brown et al.
Coherent cortical and muscle discharge in cortical myoclonus
Brain
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There are more references available in the full text version of this article.

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Rethinking the neurophysiological concept of cortical myoclonus
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Cortical myoclonus is thought to result from abnormal electrical discharges arising in the sensorimotor cortex. Given the ease of recording of cortical discharges, electrophysiological features of cortical myoclonus have been better characterized than those of subcortical forms, and electrophysiological criteria for cortical myoclonus have been proposed. These include the presence of giant somatosensory evoked potentials, enhanced long-latency reflexes, electroencephalographic discharges time-locked to individual myoclonic jerks and significant cortico-muscular connectivity. Other features that are assumed to support the cortical origin of myoclonus are short-duration electromyographic bursts, the presence of both positive and negative myoclonus and cranial-caudal progression of the jerks. While these criteria are widely used in clinical practice and research settings, their application can be difficult in practice and, as a result, they are fulfilled only by a minority of patients. In this review we reappraise the evidence that led to the definition of the electrophysiological criteria of cortical myoclonus, highlighting possible methodological incongruencies and misconceptions. We believe that, at present, the diagnostic accuracy of cortical myoclonus can be increased only by combining observations from multiple tests, according to their pathophysiological rationale; nevertheless, larger studies are needed to standardise the methods, to resolve methodological issues, to establish the diagnostic criteria sensitivity and specificity and to develop further methods that might be useful to clarify the pathophysiology of myoclonus.
Cortico-muscular coherence and brain networks in familial adult myoclonic epilepsy and progressive myoclonic epilepsy
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Familial Adult Myoclonic Epilepsy (FAME) presents with action-activated myoclonus, often associated with epilepsy, sharing various features with Progressive Myoclonic Epilepsy (PMEs), but with slower course and limited motor disability. We aimed our study to identify measures suitable to explain the different severity of FAME2 compared to EPM1, the most common PME, and to detect the signature of the distinctive brain networks.
We analyzed the EEG-EMG coherence (CMC) during segmental motor activity and indexes of connectivity in the two patient groups, and in healthy subjects (HS). We also investigated the regional and global properties of the network.
In FAME2, differently from EPM1, we found a well-localized distribution of beta-CMC and increased betweenness-centrality (BC) on the sensorimotor region contralateral to the activated hand.
In both patient groups, compared to HS, there was a decline in the network connectivity indexes in the beta and gamma band, which was more obvious in FAME2.
In FAME2, better localized CMC and increased BC in comparison with EPM1 patients could counteract the severity and the spreading of the myoclonus.
Decreased indexes of cortical integration were more severe in FAME2.
Our measures correlated with different motor disabilities and identified distinctive brain network impairments.
Rhythmic cortical myoclonus in patients with 6Q22.1 deletion
2023, European Journal of Paediatric Neurology
DNA deletions involving 6q22.1 region result in developmental encephalopathy (DE), often associated with movement disorders and epilepsy. The phenotype is attributed to the loss of the NUS1 gene included in the deleted region.
Here we report three patients with 6q22.1 deletions of variable length all showing developmental delay, and rhythmic cortical myoclonus. Two patients had generalized seizures beginning in infancy. Myoclonic jerks had polygraphic features consistent with a cortical origin, also supported by cortico-muscular coherence analysis displaying a significant peak around 20 Hz contralateral to activated segment.
Deletions in 6q22.1 region, similarly to NUS1 loss-of-function mutations, give rise to DE and cortical myoclonus via a haploinsufficiency mechanism. A phenotype of progressive myoclonic epilepsy (PME) may also occur.
Myoclonus and other jerky movement disorders
2022, Clinical Neurophysiology Practice
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.
Wearable monitoring of positive and negative myoclonus in progressive myoclonic epilepsy type 1
2021, Clinical Neurophysiology
To develop and test wearable monitoring of surface electromyography and motion for detection and quantification of positive and negative myoclonus in patients with progressive myoclonic epilepsy type 1 (EPM1).
Surface electromyography and three-dimensional acceleration were measured from 23 EPM1 patients from the biceps brachii (BB) of the dominant and the extensor digitorum communis (EDC) of the non-dominant arm for 48 hours. The patients self-reported the degree of myoclonus in a diary once an hour. Severity of myoclonus with action was evaluated by using video-recorded Unified Myoclonus Rating Scale (UMRS). Correlations of monitored parameters were quantified with the UMRS scores and the self-reported degrees of myoclonus.
The monitoring-based myoclonus index correlated significantly (p < 0.001) with the UMRS scores (ρ = 0.883 for BB and ρ = 0.823 for EDC) and with the self-reported myoclonus degrees (ρ = 0.483 for BB and ρ = 0.443 for EDC). Ten patients were assessed as probably having negative myoclonus in UMRS, while our algorithm detected that in twelve patients.
Wearable monitoring was able to detect both positive and negative myoclonus in EPM1 patients.
Our method is suitable for quantifying objective, real-life treatment effects at home and progression of myoclonus.
Morphometric analysis of spike-wave complexes (SWCs) causing myoclonic seizures in children with idiopathic myoclonic epilepsies – A positive SWC component correlates with myoclonic intensity
2021, Brain and Development
To elucidate the morphological characteristics of spike-wave complexes (SWCs) causing myoclonic seizures (MS) in childhood-onset idiopathic myoclonic epilepsies.
The subjects were 8 patients, including 4 with epilepsy with myoclonic-atonic seizures (EMAS), 3 with myoclonic epilepsy in infancy (MEI) and 1 with idiopathic unclassifiable myoclonic epilepsy. Morphometric parameters of the SWCs were compared between those with MS [SWC-MS (+)] and those without MS [SWC-MS (-)], and a correlation coefficient analysis was performed between the SWC parameters and the duration of myoclonic electromyogram (EMG) potentials.
A total of 155 SWC-MS (+) (range: 7 ∼ 34) and 80 SWC-MS (-) (10 each as a control) were analyzed. Comparison of the parameters of the SWCs between SWC-MS (+) and SWC-MS (-) demonstrated that the depth and the width of the positive-sharp-components (PSC) in the SWC-MS (+) were significantly deeper in amplitude and longer in duration than those in the SWC-MS (-), respectively, in all 8 patients (P < 0.05), whereas the number of the polyphasic-multiple-spike-components (PMSC) and the height of negative-spike-components (NSC) were not significantly different in most of the patients, respectively. The depth and the width of PSC were also significantly correlated with the duration of myoclonic EMG potentials in all patients except one [depth of PSC (n = 7): r = 0.623 ∼ 0.888; width of PSC (n = 8): r = 0.676 ∼ 0.948, P < 0.05].
This study revealed that the depth and width of PSC of the SWC are positively correlated with the MS intensity in childhood-onset idiopathic myoclonic epilepsies and are an important neurophysiological marker to generate MS.

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Original article / Article originalNeurophysiological classification of myoclonusClassification neurophysiologique des myoclonies

Abstract

Résumé

Introduction

Section snippets

Classification based on the electromyographic (EMG) correlates

Classification based on the electroencephalographic (EEG) correlates

Classification based on the jerk-locked back averaging

Classification based on the cortico-muscular coherence

Classification based on sensory evoked responses and long-loop reflexes

Paired stimulation evoked response/long-loop reflex and jerk-locked evoked responses

Transcranial magnetic stimulation (TMS)

AAEE monograph 30: electrophysiological studies of myoclonus

Muscle Nerve

Pathogenesis of giant somatosensory evoked potentials in progressive myoclonic epilepsy

Brain

Intrahemispheric and interhemispheric spread of cerebral cortical myoclonic activity and its relevance to epilepsy

Brain

Coherent cortical and muscle discharge in cortical myoclonus

Brain

Original article / Article original
Neurophysiological classification of myoclonusClassification neurophysiologique des myoclonies