Negative myoclonus. An overview of its clinical features, pathophysiological mechanisms, and management

Focal negative motor seizures: Multimodal evaluation

This case report shows the importance of multimodal evaluation to formulate a proper diagnosis of negative motor seizures (NMSs). Only few reports in literature document NMSs with video-electroencephalographic (EEG) and electromyographic coregistration. A multimodal evaluation is crucial to exclude common mimics and propose correct therapy. We describe a case of a 62-year-old man with drug-resistant focal epilepsy and NMSs, evaluated with video-EEG recording with polygraphy, magnetoencephalography (MEG), and brain magnetic resonance imaging (MRI). Video-EEG monitoring showed 182 focal NMSs, with preserved awareness and comprehension. The patient reported complex paresthesia of the left hand followed by left facial grimace, left arm flaccid paralysis, and bradycardia. EEG showed ictal discharges in the right frontocentral region associated with sudden electromyographical silence in left limb muscles consistent with loss of tonic contraction from distal to proximal muscles of the arm. MEG localized the epileptic zone in the right opercular region, consistent with MRI evidence of type II cortical dysplasia in the right inferior frontal gyrus. Multimodal evaluation is essential to document the temporal relationship between ictal discharges, clinical onset of limb paresis, and electrophysiologic evidence of loss of tonic muscular contraction. It allows definition of the specific cortical area involved in NMSs, offering new insight into physiological brain functioning.

A Reappraisal on cortical myoclonus and brief Remarks on myoclonus of different Origins

Myoclonus has multiple clinical manifestations and heterogeneous generators and etiologies, encompassing a spectrum of disorders and even physiological events. This paper, developed from a teaching course conducted by the Neurophysiology Commission of the Italian League against Epilepsy, aims to delineate the main types of myoclonus, identify potential underlying neurological disorders, outline diagnostic procedures, elucidate pathophysiological mechanisms, and discuss appropriate treatments. Neurophysiological techniques play a crucial role in accurately classifying myoclonic phenomena, by means of simple methods such as EEG plus polymyography (EEG + Polymyography), evoked potentials, examination of long-loop reflexes, and often more complex protocols to study intra-cortical inhibition-facilitation. In clinical practice, EEG + Polymyography often represents the first step to identify myoclonus, acquire signals for off-line studies and plan the diagnostic work-up.

Is High-Frequency Activity at Seizure Onset Inhibitory? A Stereoelectroencephalographic Study of Motor Cortex Seizures

OBJECTIVE

In the era of stereoelectroencephalography (SEEG), many studies have been devoted to understanding the role of interictal high-frequency oscillations. High-frequency activity (HFA) at seizure onset has been identified as a marker of epileptogenic zone. We address the physiological significance of ictal HFAs and their relation to clinical semiology.

METHODS

We retrospectively identified patients with pure focal primary motor epilepsy. We selected only patients in whom SEEG electrodes were optimally placed in the motor cortex as confirmed by electrical stimulation. Based on these narrow inclusion criteria, we extensively studied 5 patients (3 males and 2 females, mean age = 22.4 years) using time-frequency analysis and time correlation with motor signs onset.

RESULTS

A total of 157 analyzable seizures were recorded in 5 subjects. The first 2 subjects had tonic or clonic semiology with rare secondary generalization. Subject 3 had atonic onset followed by clonic hand/arm flexion. Subject 4 had clusters of tonic and atonic facial movements. Subject 5 had upper extremity tonic movements. The median frequency of the fast activity extracted from the Epileptogenic Zone Fingerprint pipeline in the first 4 subjects was 76 Hz (interquartile range = 21.9Hz). Positive motor signs did not occur concomitantly with high gamma activity developing in the motor cortex. Motor signs began at the end of HFAs.

INTERPRETATION

This study supports the hypothesis of an inhibitory effect of ictal HFAs. The frequency range in the gamma band was associated with the direction of the clinical output effect. Changes from inhibitory to excitatory effect occurred when discharge frequency dropped to low gamma or beta. ANN NEUROL 2024;95:1127-1137.

Negative Myoclonus: Neurophysiological Study and Clinical Impact in Progressive Myoclonus Ataxia

INTRODUCTION

Negative myoclonus (NM) is an involuntary movement caused by a sudden interruption of muscular activity, resulting in gait problems and falls.

OBJECTIVE

To establish frequency, clinical impact, and neurophysiology of NM in progressive myoclonus ataxia (PMA) patients.

METHODS

Clinical, neurophysiological, and genetic data of 14 PMA individuals from University Medical Centre Groningen (UMCG) Expertise Center Movement Disorder Groningen were retrospectively collected. Neurophysiological examination included video-electromyography-accelerometry assessment in all patients and electroencephalography (EEG) examination in 13 individuals. Jerk-locked (or silent period-locked) back-averaging and cortico-muscular coherence (CMC) analysis aided the classification of myoclonus.

RESULTS

NM was present in 6 (NM+) and absent in 8 (NM-) PMA patients. NM+ individuals have more frequent falls (100% vs. 37.5%) and higher scores on the Gross Motor Function Classification System (GMFCS) (4.3 ±0.74 vs. 2.5 ±1.2) than NM- individuals. Genetic background of NM+ included GOSR2 and SEMA6B, while that of NM- included ATM, KCNC3, NUS1, STPBN2, and GOSR2. NM was frequently preceded by positive myoclonus (PM) and silent-period length was between 88 and 194 ms. EEG epileptiform discharges were associated with NM in 2 cases. PM was classified as cortical in 5 NM+ and 2 NM- through EEG inspection, jerk-locked back-averaging, or CMC analysis.

DISCUSSION

Neurophysiological examination is crucial for detecting NM that could be missed on clinical examination due to a preceding PM. Evidence points to a cortical origin of NM, an association with more severe motor phenotype, and suggests the presence of genetic disorders causing either a PMA or progressive myoclonus epilepsy, rather than pure PMA phenotype. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Knee Buckling as an Atypical Adverse Effect of Clozapine: A Case Report

Clozapine has become a widely popular and effective medication in the treatment of refractory schizophrenia and refractory bipolar disorder. Although the use of clozapine proves to be an effective resort, it has to be closely monitored due to its narrow therapeutic range and multiple dangerous adverse effects. In rare cases, clozapine has been known to cause an antagonistic myoclonic jerk that leads to knee buckling. Here, we present the case of a 29-year-old female who is being treated for schizoaffective disorder, bipolar, manic type, who reported two instances of knee buckling associated with falls while taking clozapine.

Flapping Tremor: Unraveling Asterixis-A Narrative Review

Asterixis is a subtype of negative myoclonus characterized by brief, arrhythmic lapses of sustained posture due to involuntary pauses in muscle contraction. We performed a narrative review to characterize further asterixis regarding nomenclature, historical aspects, etiology, pathophysiology, classification, diagnosis, and treatment. Asterixis has been classically used as a synonym for negative myoclonus across the literature and in previous articles. However, it is important to distinguish asterixis from other subtypes of negative myoclonus, for example, epileptic negative myoclonus, because management could change. Asterixis is not specific to any pathophysiological process, but it is more commonly reported in hepatic encephalopathy, renal and respiratory failure, cerebrovascular diseases, as well as associated with drugs that could potentially lead to hyperammonemia, such as valproic acid, carbamazepine, and phenytoin. Asterixis is usually asymptomatic and not spontaneously reported by patients. This highlights the importance of actively searching for this sign in the physical exam of encephalopathic patients because it could indicate an underlying toxic or metabolic cause. Asterixis is usually reversible upon treatment of the underlying cause.

Detecting negative myoclonus during long-term home measurements using wearables

OBJECTIVE

The aim of this study was to develop a feasible method for the detection of negative myoclonus (NM) through long-term home measurements in patients with progressive myoclonus epilepsy type 1.

METHODS

The number and duration of silent periods (SP) associated with NM were detected during a 48 h home recording using wearable surface electromyography (EMG) sensors.

RESULTS

A newly developed algorithm was able to find short (50-69 ms), intermediate (70-100 ms), and long (101- 500 ms) SPs from EMG data. Negative myoclonus assessed by the algorithm correlated significantly with the video-recorded and physician-evaluated unified myoclonus rating scale (UMRS) scores of NM and action myoclonus. Silent period duration, number, and their combination, correlated strongly and significantly also with the Singer score, which assesses functional status and ambulation.

CONCLUSIONS

Negative myoclonus can be determined objectively using long-term EMG measurements in home environment. With long-term measurements, we can acquire more reliable quantified information about NM as a symptom, compared to short evaluation at the clinic.

SIGNIFICANCE

As measured using SPs, NM may be a clinically useful measure for monitoring disease progression or assessing antimyoclonic drug effects objectively.

Long-standing myoclonic hand tremor as an isolated symptom of hypertrophic olivary degeneration

Hypertrophic olivary degeneration (HOD) is a rare condition caused by lesions of the dentato-rubro-olivary pathway, usually bilateral. We presented a case of a 64-year old male with HOD caused by a unilateral, posterior pontine cavernoma. The patient has not developed the typical palate myoclonus until recently. Isolated hand myoclonus with coexisting asterixis was present for years. This case shows unique HOD symptomatology and emphasizes the important role of MRI in the differential diagnosis of monomelic myoclonus.

Unilateral asterixis in a patient with subdural hematoma: A case of epileptic negative myoclonus

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Negative myoclonus causes locomotory disability in progressive myoclonus epilepsy type EPM1- Unverricht-Lundborg disease

OBJECTIVE

Patients with Unverricht-Lundborg disease/EPM1 develop increasing locomotory disability or ataxia in the course of their disease. To test our hypothesis that negative myoclonus is the reason for this increasing ataxia, we investigated a possible correlation over time.

METHODS

In 15 patients with EPM1who were confirmed to have a mutation in the CSTB gene, polygraphic video-EEG-EMG recordings were performed in freely moving or standing patients. The criterion for the duration of the negative myoclonus was the measured length of the silent periods on the EMG.

RESULTS

All 15 patients had documented negative myoclonus when standing and walking. The mean duration of silent periods significantly increased from 100 (SD: 19.1) ms at time point T1 to 128 (SD: 26.6) ms at T2 in seven of eight patients, based on two recordings and a mean interval of 12.8 (SD: 4.9) years. Using a cross-sectional approach, all 15 patients were classified based on whether they were ambulatory, could walk with aid, or needed a wheelchair. Ambulatory patients had a mean duration of 97.3 (SD: 16.5) ms, patients who could walk with aid had a mean duration of 106.7 (SD: 16) ms, and patients who were wheelchair-bound had a mean duration of 138 (SD: 23.6) ms. In addition to the prolongation of the silent periods, there was an observed increase in frequency of the negative myoclonus, becoming more continuous and tremulous.

SIGNIFICANCE

Using simultaneous EEG/EMG recordings in freely moving or standing patients, we have shown that the locomotor disability or ataxia is due to negative myoclonus in voluntary innervated muscles. The reason for the progression is the prolongation of the silent periods as measured by the duration of the negative myoclonus and their increase in frequency.

Wearable monitoring of positive and negative myoclonus in progressive myoclonic epilepsy type 1

OBJECTIVE

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).

METHODS

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.

RESULTS

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.

CONCLUSIONS

Wearable monitoring was able to detect both positive and negative myoclonus in EPM1 patients.

SIGNIFICANCE

Our method is suitable for quantifying objective, real-life treatment effects at home and progression of myoclonus.

Negative myoclonus as the leading symptom in acute cefepime neurotoxicity

An 86-year-old woman was diagnosed with hospital-acquired pneumonia with Pseudomonas aeruginosa and treated with cefepime adjusted to her renal clearance. After 4 days, she developed acute-onset negative myoclonus without signs of altered mental status. After ruling out an acute intracranial haemorrhagic or ischaemic stroke as well as other metabolic and endocrine causes of negative myoclonus, the antibiotic was switched to piperacillin/tazobactam due to a suspicion of cefepime neurotoxicity. The patient improved within 24 hours and her symptoms fully resolved within 4 days. These observations suggest a link of the negative myoclonus to acute cefepime neurotoxicity, which may occur without or with minimal alteration of mental status, thus extending its spectrum of clinical presentation.

Self-limited epilepsy with centro-temporal spikes: A study of 46 patients with unusual clinical manifestations

PURPOSE

We retrospectively analyzed the seizure characteristics, EEG pattern, treatment, and outcome in a series of patients with self-limited epilepsy with centrotemporal spikes (SLECTS) who presented with unusual clinical manifestations.

METHOD

A retrospective, descriptive, multicenter study was conducted evaluating 46 patients with SLECTS who had seizures with an unusual semiology. We collected data from patients with SLECTS seen at eight Argentine centers between April 1998 and April 2018.

RESULTS

Thirteen patients (28.2 %) had seizures with affective symptoms characterized by sudden fright and autonomic disturbances and mild impairment of consciousness. Eleven patients (24.8 %) had frequent seizures characterized by unilateral facial sensorimotor symptoms, oropharyngolaryngeal manifestations, and speech arrest with sialorrhea only when awake. Seven patients (15.3 %) started with opercular epileptic status with unilateral or bilateral clonic seizures of the mouth with speech arrest and sialorrhea when awake and during sleep. Seven patients (15.3 %) had postictal Todd's paralysis after unilateral clonic seizures with facial and limb movements lasting between 60 min and 130 min. Six patients (13 %) had negative myoclonus, two in a unilateral upper limb, two in a unilateral lower limb, and the remaining two patients had frequent falls. One patient (2.1 %) had focal sensorimotor seizures characterized by unilateral numbness in the cheeks and one upper limb, additional to unilateral facial clonic seizures, speech arrest, and sialorrhea. The remaining patient (2.1 %) had sporadic focal tonic-dystonic seizures in the left upper limb only during sleep.

CONCLUSION

In our study, we found evidence of the existence of unusual clinical cases of SLECTS with typical EEG patterns and an excellent prognosis.

Functional Neural Changes after Low-Frequency Bilateral Globus Pallidus Internus Deep Brain Stimulation for Post-Hypoxic Cortical Myoclonus: Voxel-Based Subtraction Analysis of Serial Positron Emission

Post-hypoxic myoclonus (PHM) and Lance–Adams syndrome (LAS) are rare conditions following cardiopulmonary resuscitation. The aim of this study was to identify functional activity in the cerebral cortex after a hypoxic event and to investigate alterations that could be modulated by deep brain stimulation (DBS). A voxel-based subtraction analysis of serial positron emission tomography (PET) scans was performed in a 34-year-old woman with chronic medically refractory PHM that improved with bilateral globus pallidus internus (Gpi) DBS implanted three years after the hypoxic event. The patient required low-frequency stimulation to show myoclonus improvement. Using voxel-based statistical parametric mapping, we identified a decrease in glucose metabolism in the prefrontal lobe including the dorsolateral, orbito-, and inferior prefrontal cortex, which was suspected to be the origin of the myoclonus from postoperative PET/magnetic resonance imaging (MRI) after DBS. Based on the present study results, voxel-based subtraction of PET appears to be a useful approach for monitoring patients with PHM treated with DBS. Further investigation and continuous follow-up on the use of PET analysis and DBS treatment for patients with PHM are necessary to help understanding the pathophysiology of PHM, or LAS.

Negative myoclonus associated with tramadol use

Negative myoclonus (NM) is a shock-like jerky involuntary movement caused by a sudden, brief interruption of tonic muscle contraction. NM is observed in patients diagnosed with epilepsy, metabolic encephalopathy, and drug toxicity and in patients with brain lesions. A 55-year-old man presented with NM in both his arms and neck. He has taken medications containing tramadol at a dose of 80–140 mg/day for 5 days due to common cold. He had no history of seizures. Acute lesions were not observed during magnetic resonance imaging, and abnormal findings in his laboratory tests were not noted. His NM resolved completely after the discontinuation of tramadol and the oral administration of clonazepam. Our case report suggests that tramadol can cause NM in patients without seizure history or metabolic disorders, even within its therapeutic dose.

Tremor and myoclonus

Tremor and myoclonus are two common hyperkinetic movement disorders. Tremor is characterized by rhythmic oscillatory movements while myoclonic jerks are usually arrhythmic. Tremor can be classified into subtypes including the most common types: essential, enhanced physiological, and parkinsonian tremor. Myoclonus classification is based on its anatomic origin: cortical, subcortical, spinal, and peripheral myoclonus. The clinical presentations are unfortunately not always classic and electrophysiologic investigations can be helpful in making a phenotypic diagnosis. Video-polymyography is the main technique to (sub)classify the involuntary movements. In myoclonus, advanced electrophysiologic testing, such as back-averaging, coherence analysis, somatosensory-evoked potentials, and the C-reflex can be of additional value. Recent developments in tremor point toward a role for intermuscular coherence analysis to differentiate between tremor subtypes. Classification of the movement disorder based on clinical and electrophysiologic features is important, as it enables the search for an etiological diagnosis and guides tailored treatment.

Negative myoclonus associated with pregabalin

Negative myoclonus (NM) is a jerky, shock-like involuntary movement caused by a sudden, brief interruption of muscle contraction. An 80-year-old man presented with multifocal NM and confusion. Two days before the onset of NM, he commenced the intake of pregabalin at a dose of 150 mg/day for neuropathic pain. His NM resolved completely and mental status improved gradually after the administration of lorazepam intravenously and the discontinuation of pregabalin. Our study suggests that pregabalin can cause NM even in patients without a history of seizures.

Epileptic negative myoclonus restricted to lower limbs in benign childhood focal epilepsy with vertex spikes

BACKGROUND AND PURPOSE

The aim was to determine the electroclinical findings in benign childhood focal epilepsy with vertex spikes (BEVS) with epileptic negative myoclonus (ENM) restricted to the lower limbs.

METHODS

The electroencephalogram database of Peking University First Hospital and medical records of patients with BEVS and ENM restricted to the lower limbs were reviewed.

RESULTS

Twenty-seven patients with BEVS had ENM restricted to the lower limbs. Twelve started as ENM restricted to the lower limbs. The age at seizure onset ranged from 1.5 to 4.8 years. During the course, half of the 12 patients developed focal sensorimotor seizures and then were diagnosed as benign childhood epilepsy with centrotemporal spikes (BECTS), with BEVS (four cases) and without BEVS (two cases). Five of them had electrical status epilepticus during sleep (ESES) and met the diagnostic criteria of atypical benign partial epilepsy (ABPE). Fifteen of the 27 patients had ENM restricted to the lower limbs during the course. The age at seizure onset ranged from 1.3 to 9.8 years. All had ESES and were diagnosed as ABPE, 11 as ABPE with BEVS and four as ABPE evolving into BEVS.

CONCLUSIONS

Benign childhood focal epilepsy with vertex spikes (BEVS) might represent a specific epileptic syndrome of the continuum of benign childhood focal epilepsy. ENM restricted to the lower limbs was a special phenomenon in BEVS. BEVS could overlap with BECTS or evolve into BECTS and further into ABPE and vice versa. Ignorance of vertex spikes with associated ENM restricted to the lower limbs might lead to a misunderstanding of BEVS, a specific type of benign childhood focal epilepsy.

Treatment Strategies for Dravet Syndrome

Dravet syndrome (DS) is a medically refractory epilepsy that onsets in the first year of life with prolonged seizures, often triggered by fever. Over time, patients develop other seizure types (myoclonic, atypical absences, drops), intellectual disability, crouch gait and other co-morbidities (sleep problems, autonomic dysfunction). Complete seizure control is generally not achievable with current therapies, and the goals of treatment are to balance reduction of seizure burden with adverse effects of therapies. Treatment of co-morbidities must also be addressed, as they have a significant impact on the quality of life of patients with DS. Seizures are typically worsened with sodium-channel agents. Accepted first-line agents include clobazam and valproic acid, although these rarely provide adequate seizure control. Benefit has also been noted with stiripentol, topiramate, levetiracetam, the ketogenic diet and vagal nerve stimulation. Several agents presently in development, specifically fenfluramine and cannabidiol, have shown efficacy in clinical trials. Status epilepticus is a recurring problem for patients with DS, particularly in their early childhood years. All patients should be prescribed a home rescue therapy (usually a benzodiazepine) but should also have a written seizure action plan that outlines when rescue should be given and further steps to take in the local hospital if the seizure persists despite home rescue therapy.

Negative myoclonus induced by gabapentin and pregabalin: A case series and systematic literature review

INTRODUCTION

Negative myoclonus is a jerky, brief, and sudden interruption of voluntary muscle contraction. Although gabapentin and pregabalin have been reported to induce positive myoclonus in some patients with impaired renal function, there are only a few studies describing pregabalin- or gabapentin-induced negative myoclonus. This study reviewed patients who had developed pregabalin- or gabapentin-induced negative myoclonus.

METHODS

We collected the patients with negative myoclonus who were referred to the department of neurology at a university-affiliated hospital and selected pregabalin- or gabapentin-induced negative myoclonus. Then reviewed the literature with respect to pregabalin- or gabapentin-induced negative myoclonus.

RESULTS

A total of 77 patients with negative myoclonus were reviewed. Among them, 21 neuropathic pain patients who were prescribed and developed negative myoclonus induced by pregabalin (9 cases) or gabapentin (12 cases). To prove causality of the drug, probable and certain level of category according to the WHO-UMC criteria were recruited. Of the 21 patients, 3 had impaired renal function, while 18 had normal renal function. Review of the literature identified 7 further cases (6 had normal renal function) with pregabalin- or gabapentin-induced negative myoclonus.

CONCLUSION

Pregabalin- and gabapentin-induced negative myoclonus can develop even in patients with normal renal function. Physicians should keep in mind the possibility of patients developing negative myoclonus under treatment of pregabalin or gabapentin even in short period of time and with low dosage, and in the normal range of renal function. Further prospective study investigating incidence and risk factors is warranted.

Negative Myoclonus Induced by Ciprofloxacin

BACKGROUND

Negative myoclonus is characterized by a brief sudden loss of muscle activity, and can be caused by a variety of acquired factors and epilepsy syndromes.

PHENOMENOLOGY SHOWN

We show a clear video example of a patient with an extensive negative myoclonus that was induced by ciprofloxacin.

EDUCATIONAL VALUE

Several neurotoxic effects have been associated with the use of ciprofloxacin, but negative myoclonus has not been reported previously.

Improvement of Post-hypoxic Myoclonus with Bilateral Pallidal Deep Brain Stimulation: A Case Report and Review of the Literature

Background

Post-hypoxic myoclonus (PHM) is a syndrome that occurs when a patient has suffered hypoxic brain injury. The myoclonus is usually multifocal and generalized, often stemming from both cortical and subcortical origins. In severe cases, pharmacological treatments with antiepileptic medications may not satisfactorily control the myoclonus.

Methods

We present a case of a 23-year-old male with chronic medication refractory PHM following a cardiopulmonary arrest related to an asthmatic attack who improved with bilateral globus pallidus internus (GPi) deep brain stimulation (DBS). We review the clinical features of PHM, as well as the preoperative and postoperative Unified Myoclonus Rating Scale scores and DBS programming parameters in this patient and compare them with the three other published PHM-DBS cases in the literature.

Results

This patient experienced an alleviation of myoclonic jerks at rest and a 39% reduction in action myoclonus with improvement in both positive and negative myoclonus with bilateral GPi-DBS. High frequency stimulation (130 Hz) with amplitudes >2.5 V were needed for the therapeutic response.

Discussion

We demonstrate a robust improvement in a medication refractory PHM patient with bilateral GPi-DBS, and suggest that it is a viable therapeutic option for debilitating post-hypoxic myoclonus.

Dopaminergic medication unrelated myoclonus is less related to tremor in idiopathic Parkinson's disease

Myoclonus in Parkinson's disease (PD) may be related or unrelated to dopaminergic medication and may share some features of cortical myoclonus. The aim of this study was to analyze clinical and electrophysiological correlates of the dopaminergic treatment unrelated myoclonus in PD patients. We included 17 PD patients with the end-of-dose myoclonus and 16 PD patients without myoclonus between January 2010 and June 2011. Surface electromyography of upper extremity muscles and long latency reflexes (LLRs) were performed. Positive or negative myoclonus with a duration of 35-100 ms was observed. Rest tremor was less frequent in the group with myoclonus. Only one PD patient with myoclonus had C reflex. Mean LLR amplitude was significantly high in PD with myoclonus compared to the group without myoclonus (p = 0.024). Dopaminergic treatment unrelated myoclonus is less related to rest tremor in PD, may be positive or negative, and exhibits similar features to cortical myoclonus.

A novel diagnostic approach to patients with myoclonus

Myoclonus is a hyperkinetic movement disorder characterized by brief, involuntary muscular jerks. Recognition of myoclonus and determination of the underlying aetiology remains challenging given that both acquired and genetically determined disorders have varied manifestations. The diagnostic work-up in myoclonus is often time-consuming and costly, and a definitive diagnosis is reached in only a minority of patients. On the basis of a systematic literature review up to June 2015, we propose a novel diagnostic eight-step algorithm to help clinicians accurately, efficiently and cost-effectively diagnose myoclonus. The large number of genes implicated in myoclonus and the wide clinical variation of these genetic disorders emphasize the need for novel diagnostic techniques. Therefore, and for the first time, we incorporate next-generation sequencing (NGS) in a diagnostic algorithm for myoclonus. The initial step of the algorithm is to confirm whether the movement disorder phenotype is consistent with, myoclonus, and to define its anatomical subtype. The next steps are aimed at identification of both treatable acquired causes and those genetic causes of myoclonus that require a diagnostic approach other than NGS. Finally, other genetic diseases that could cause myoclonus can be investigated simultaneously by NGS techniques. To facilitate NGS diagnostics, we provide a comprehensive list of genes associated with myoclonus.

Clinical characteristics and etiology of transient myoclonic state in the elderly

OBJECTIVES

To clarify clinical picture of transient myoclonic state in elderly patients.

METHODS

The Aizawa Hospital database was searched to identify all patients with transient myoclonic state with or without asterixis between April 2006 and June 2013. Medical records, brain images and laboratory data including electroencephalograms and electromyograms were reviewed.

RESULTS

We found 26 patients: 10 women and 16 men, and their ages ranged from 56 to 96 years (79.7 ± 9.9 years, mean ± standard deviation). The affected sites of the myoclonic jerks were predominantly the lower face, neck and upper extremities. The myoclonus appeared at conscious resting condition, slightly exaggerated by posturing or action. Asterixis was observed in eight patients. Single myoclonic bursts were 1.70 ± 0.94 s long. The interval of myoclonic bursts was 4.47 ± 2.44 s. Single myoclonic bursts were composed of 9.5 ± 2.5 Hz myoclonic contractions, and single myoclonic contractions were 44.4 ± 12.3 ms in duration. Most of the patients suffered from chronic diseases, but they were basically independent in activity of daily living. Oral administration of clonazepam was effective.

CONCLUSIONS

Transient myoclonic state has relatively stereotyped features. The pathophysiology may include some metabolic abnormality on a background of age-related arteriosclerotic changes. Its prognosis is benign, and prompt oral administration of clonazepam abolishes it. Further investigations will be needed to clarify its cause and pathophysiology.

Myoclonus

Myoclonus is a hyperkinetic movement disorder characterized by quick, involuntary jerks. It encompasses a vast range of etiologies and widespread anatomic locations. Treatment frequently requires multiple agents and is often only partially beneficial. These patients pose a considerable challenge for the clinician, further complicated by the fact that many of the treatment choices lack evidence-based support. In the past few years, publications regarding therapy have been largely observational case reports or series. Although the literature on treatment of cortical myoclonus appears to be growing, evidence regarding myoclonus of noncortical origin is less well established. Investigation of more satisfactory treatments is needed, as this condition can be disturbing, debilitating, and sometimes harmful for patients. Continuing investigations are using various animal models (mostly of posthypoxic myoclonus), electrophysiologic studies, new imaging techniques such as diffusion tensor imaging, and genetic studies. Meanwhile, the clinical approach to diagnosing and classifying myoclonus remains largely unchanged. This review updates readers on current investigations and suggests guidelines for diagnosing and treating myoclonus.

Myoclonic disorders: a practical approach for diagnosis and treatment

Myoclonus is a sudden, brief, involuntary muscle jerk. It is caused by abrupt muscle contraction, in the case of positive myoclonus, or by sudden cessation of ongoing muscular activity, in the case of negative myoclonus (NM). Myoclonus may be classified in a number of ways, although classification based on the underlying physiology is the most useful from the therapeutic viewpoint. Given the large number of possible causes of myoclonus, it is essential to take a good history, to clinically characterize myoclonus and to look for additional findings on examination in order to limit the list of possible investigations. With regards to the history, the age of onset, the character of myoclonus, precipitating or alleviating factors, family history and associated symptoms and signs are important. On examination, it is important to see whether the myoclonus appears at rest, on keeping posture or during action, to note the distribution of jerks and to look for the stimulus sensitivity. Electrophysiological tests are very helpful in determining whether myoclonus is cortical, subcortical or spinal. A single pharmacological agent rarely control myoclonus and therefore polytherapy with a combination of drugs, often in large dosages, is usually needed. Generally, antiepileptic drugs such as valproate, levetiracetam and piracetam are effective in cortical myoclonus, but less effective in other forms of myoclonus. Clonazepam may be helpful with all types of myoclonus. Focal and segmental myoclonus, irrespective of its origin, may be treated with botulinum toxin injections, with variable success.

Unilateral negative myoclonus caused by herpes simplex virus encephalitis

Various neurologic manifestations of herpes simplex virus (HSV) encephalitis have been reported on the literatures. Chorea, ballism, choreoathetosis and myoclonus were reported as movement disorders which might be related with brain lesion by HSV encephalitis, but negative myoclonus (NM) has never been reported before. NM can be characterized as a shock-like involuntary jerky movement caused by a sudden, brief interruption of muscle activity. We experienced a case of HSV encephalitis with NM in unilateral arm and leg. In polygraphic monitoring, electroencephalography (EMG) silent periods are 50–250 ms in duration with no detectable EMG correlate.

Management of patients with myoclonus: available therapies and the need for an evidence-based approach

Myoclonus is a hyperkinetic movement disorder characterised by quick and involuntary jerks. Therapy should focus on cure of an underlying disorder; however, symptomatic treatment is often needed when treatment of an underlying cause is impossible or ineffective. The appropriate treatment for a specific type of myoclonus is based on the classification of the anatomical origin of the myoclonus: cortical, subcortical, spinal, or peripheral. We outline criteria for classification and present an overview of the available therapeutic options for the different types of myoclonus. Because of a generally low level of evidence, therapeutic options mainly rely on small observational studies and expert opinion. For an evidence-based approach in the future, randomised controlled trials of symptomatic therapies for myoclonus in homogeneous patient groups are needed.

Acute transient deafness representing a negative epileptic phenomenon

We report herein 2 children who presented with acute deafness heralding an epileptic event manifesting thereafter by loss of consciousness and tonic generalized posturing, possibly reflecting a negative epileptic phenomenon. The first previously healthy male had 2 paroxysmal episodes 7 months apart, starting with acute deafness lasting for a few minutes followed by loss of consciousness and generalized tonic posturing for 10 minutes. Electroencephalography (EEG) during the second episodes demonstrated generalized epileptiform discharges. The second with previously controlled partial complex seizures presented with episodes of complete deafness lasting for a few minutes followed by loss of consciousness and focal tonic posturing lasting 10 minutes. Such acute deafness represented an aura of a focal seizure substantiated by right focal temporal epileptic discharges within the region of the primary auditory cortex. Therefore, EEG should be performed in any case of acute transient deafness, even in the absence of accompanying overt clinical seizures.

Epileptic negative myoclonus as the presenting seizure type in rolandic epilepsy

Epileptic negative myoclonus is an uncommon seizure type characterized by a sudden, brief loss of muscle tone that may lead to falling. It has been associated largely with benign childhood epilepsy with centrotemporal spikes (rolandic epilepsy), although it may also be a feature of other epileptic syndromes. In patients with rolandic epilepsy, epileptic negative myoclonus usually appears during the course of the disease, well after a diagnosis of the epilepsy has been established. Described here are five patients with rolandic epilepsy in which the presenting seizure was falls due to epileptic negative myoclonus. Because developmental delay or neurocognitive problems were present in three of the children, it is possible that epileptic negative myoclonus may be misinterpreted as clumsiness-related falls in some children who actually have undiagnosed rolandic epilepsy.

A study on epileptic negative myoclonus in atypical benign partial epilepsy of childhood

OBJECTIVE

To investigate the clinical and neurophysiological characteristics, particularly therapeutic considerations, of epileptic negative myoclonus (ENM) in atypical benign partial epilepsy (ABPE) of childhood.

METHODS

From 1998 to 2006, 14/242 patients with benign children epilepsy with centrotemporal spikes (BECTS) were diagnosed as having ABPE with ENM. In all 14 patients, we performed video-EEG monitoring along with tests with the patient's arms outstretched; 6/14 patients were also simultaneously underwent surface electromyogram (EMG). ENM manifestations, electrophysiological features, and responses to antiepileptic drugs were analyzed.

RESULTS

In all cases, ENM developed after the onset of epilepsy and during antiepileptic drug therapy, and the appearance of ENM were corresponding to EEG findings of high-amplitude spikes followed by a slow wave in the contralateral motor areas with secondary generalization. This was further confirmed by time-locked silent EMG. During ENM occurrence or recurrence, habitual seizures and interictal discharges were exaggerated. In some patients, the changes in antiepileptic drug regimens in relation to ENM appearance included add-on therapy with carbamazepine, oxcarbazepine, and phenobarbital or withdrawal of valproate. ENM was controlled in most cases by administration of various combinations of valproate, clonazepam, and corticosteroids.

CONCLUSION

The incidence of ENM or ABPE in our center was approximately 5.79%. A combination of video-EEG monitoring with the patient's arms outstretched and EMG is essential to identify ENM. The aggravation of habitual seizures and interictal discharges indicate ENM. Some antiepileptic drugs, such as carbamazepine, oxcarbazepine, and phenobarbital, may be related to ENM occurrence during spontaneous aggravation of ABPE. Various combinations of valproate, benzodiazepines, and corticosteroids are relatively effective for treating ENM that occurs in ABPE.

Pregabalin-induced cortical negative myoclonus in a patient with neuropathic pain

Myoclonus is a well-known side effect of anticonvulsant drugs. Pregabalin is one of the newer drugs approved for the treatment of focal epilepsies. Frequently it is also used to treat chronic pain syndromes. We describe a patient who, after receiving his first dose of pregabalin to relieve neuropathic pain, presented with a negative myoclonus. Clinical aspects and electrophysiological data such as polygraphic studies, electroencephalography, and measurement of somatosensory evoked potentials support the cortical origin of negative myoclonus. Our findings reveal that even in patients without a history of seizures, pregabalin can cause a cortical negative myoclonus.

Ethosuximide: from bench to bedside

Ethosuximide, 2-ethyl-2-methylsuccinimide, has been used extensively for "petit mal" seizures and it is a valuable agent in studies of absence epilepsy. In the treatment of epilepsy, ethosuximide has a narrow therapeutic profile. It is the drug of choice in the monotherapy or combination therapy of children with generalized absence (petit mal) epilepsy. Commonly observed side effects of ethosuximide are dose dependent and involve the gastrointestinal tract and central nervous system. Ethosuximide has been associated with a wide variety of idiosyncratic reactions and with hematopoietic adverse effects. Typical absence seizures are generated as a result of complex interactions between the thalamus and the cerebral cortex. This thalamocortical circuitry is under the control of several specific inhibitory and excitatory systems arising from the forebrain and brainstem. Corticothalamic rhythms are believed to be involved in the generation of spike-and-wave discharges that are the characteristic electroencephalographic signs of absence seizures. The spontaneous pacemaker oscillatory activity of thalamocortical circuitry involves low threshold T-type Ca2+ currents in the thalamus, and ethosuximide is presumed to reduce these low threshold T-type Ca2+ currents in thalamic neurons. Ethosuximide also decreases the persistent Na+ and Ca2+ -activated K+ currents in thalamic and layer V cortical pyramidal neurons. In addition, there is evidence that in a genetic absence epilepsy rat model ethosuximide reduces cortical gamma-aminobutyric acid (GABA) levels. Also, elevated glutamate levels in the primary motor cortex of rats with absence epilepsy (but not in normal animals) are reduced by ethosuximide.