Myoclonus

Myoclonus After Cardiac Arrest: Need for Standardization-A Systematic Review and Research Proposal on Terminology

OBJECTIVES

Although myoclonus less than or equal to 72 hours after cardiac arrest (CA) is often viewed as a single entity, there is considerable heterogeneity in its clinical and electrophysiology characteristics, and its strength of association with outcome. We reviewed definitions, electroencephalogram, and outcome of myoclonus post-CA to assess the need for consensus and the potential role of electroencephalogram for further research.

DATA SOURCES

PubMed, Embase, and Cochrane databases.

STUDY SELECTION

English-language adult (≥ 18 yr) studies from 1966 to May 31, 2024, reporting myoclonus, myoclonic status/status myoclonus (MyS/SM), myoclonic status epilepticus (MSE), and/or early Lance-Adams Syndrome (eLAS) less than or equal to 72 hours post-CA. All study designs were independently screened by two authors.

DATA EXTRACTION

Data on patients presenting myoclonus, MyS/SM, MSE, and eLAS less than or equal to 72 hours post-CA, along with their definitions, electroencephalogram, and outcomes were extracted. The Newcastle-Ottawa Scale and Cochrane-Risk-of-Bias Assessment tool were used to evaluate study quality (PROSPERO n.CRD42023438107).

DATA SYNTHESIS

Of 585 identified articles, 119 met the inclusion criteria, revealing substantial heterogeneity in definitions, electroencephalogram, and outcomes. Among 3881 patients, myoclonus was reported in 2659, MyS/SM in 883, MSE in 569, and eLAS in 40. Among patients with a defined outcome, a Cerebral Performance Category (CPC) scale of 1-2 was reported in 9.8% of patients with myoclonus, 5.8% with MyS/SM, 5.7% with MSE, and 82.0% with eLAS. Electroencephalogram was recorded in 2714 patients (69.9%). CPC of 1-2 was observed in 1.6% of patients with suppression/suppression burst (SB)/unreactive (U) electroencephalogram, 11.3% with non-SB/U electroencephalogram and status epilepticus (SE), and 22.3% with non-SB/U electroencephalogram without SE.

CONCLUSIONS

Heterogeneity in definitions resulted in weak associations with outcomes. We propose to investigate myoclonus by including related electroencephalogram patterns: myoclonus associated with suppression/SB background electroencephalogram, myoclonus with nonsuppression/SB background but SE-electroencephalogram, and myoclonus with nonsuppression/SB background without SE-electroencephalogram. This pragmatic research approach should be validated in future studies.

Frequency of Myoclonus and its Countermeasures in Terminally Ill Patients with Cancer: A Single-Center Retrospective Study

Myoclonus is a relatively rare involuntary movement that is often observed in palliative care settings and that can cause patient distress. The purpose of this study is to investigate the occurrence of myoclonus and countermeasures against it in terminally ill patients with cancer diagnosed by palliative care specialists at Komaki City Hospital, Japan. We retrospectively reviewed patients with terminal cancer who received palliative care consultations between January 2018 and May 2019 and who were diagnosed with myoclonus by palliative care specialists, using electronic medical records. Patient demographics, time from onset of myoclonus to death, daily opioid use, countermeasures, and outcome of myoclonus were assessed. Of 360 patients examined during this period, 45 (12.5%) were diagnosed with myoclonus. Median age was 71 (range, 43-88) years; median time from onset of myoclonus to death was 8 days (range, 0-56); opioid usage was present in 39 patients (morphine, oxycodone, and fentanyl: n = 6, 21, and 12, respectively); and median oral morphine equivalent at onset of myoclonus was 60 mg (range, 12-336 mg). Myoclonus treatment was administered to 21 patients (opioid dose reduction, opioid switching, and others: n = 14, 3, and 4, respectively). Myoclonus is a common complication in patients with terminal cancer.

Opioid-induced Neurotoxicity in Patients with Cancer Pain

OPINION STATEMENT

Opioid-induced neurotoxicity (OINT) is a neuropsychiatric syndrome observed with opioid therapy. The mechanism of OINT is thought to be multifactorial, and many risk factors may facilitate its development. If symptoms of OINT are seen, the prescriber should consider hydration, discontinuation of the offending opioid drug, or switching of opioid medication, or the use of some adjuvants. Multiple factors like inter- and intraindividual differences in opioid pharmacology may influence the accuracy of dose calculations for opioid switching. Experience and clinical judgment in a specialistic palliative care setting should be used and individual patient characteristics considered when applying any conversion table.

Nomenclature of Genetic Movement Disorders: Recommendations of the International Parkinson and Movement Disorder Society Task Force - An Update

In 2016, the Movement Disorder Society Task Force for the Nomenclature of Genetic Movement Disorders presented a new system for naming genetically determined movement disorders and provided a criterion-based list of confirmed monogenic movement disorders. Since then, a substantial number of novel disease-causing genes have been described, which warrant classification using this system. In addition, with this update, we further refined the system and propose dissolving the imaging-based categories of Primary Familial Brain Calcification and Neurodegeneration with Brain Iron Accumulation and reclassifying these genetic conditions according to their predominant phenotype. We also introduce the novel category of Mixed Movement Disorders (MxMD), which includes conditions linked to multiple equally prominent movement disorder phenotypes. In this article, we present updated lists of newly confirmed monogenic causes of movement disorders. We found a total of 89 different newly identified genes that warrant a prefix based on our criteria; 6 genes for parkinsonism, 21 for dystonia, 38 for dominant and recessive ataxia, 5 for chorea, 7 for myoclonus, 13 for spastic paraplegia, 3 for paroxysmal movement disorders, and 6 for mixed movement disorder phenotypes; 10 genes were linked to combined phenotypes and have been assigned two new prefixes. The updated lists represent a resource for clinicians and researchers alike and they have also been published on the website of the Task Force for the Nomenclature of Genetic Movement Disorders on the homepage of the International Parkinson and Movement Disorder Society (https://www.movementdisorders.org/MDS/About/Committees--Other-Groups/MDS-Task-Forces/Task-Force-on-Nomenclature-in-Movement-Disorders.htm). © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

Physiology-Based Treatment of Myoclonus

Myoclonus can cause significant disability for patients. Myoclonus has a strikingly diverse array of underlying etiologies, clinical presentations, and pathophysiological mechanisms. Treatment of myoclonus is vital to improving the quality of life of patients with these disorders. The optimal treatment strategy for myoclonus is best determined based upon careful evaluation and consideration of the underlying etiology and neurophysiological classification. Electrophysiological testing including EEG (electroencephalogram) and EMG (electromyogram) data is helpful in determining the neurophysiological classification of myoclonus. The neurophysiological subtypes of myoclonus include cortical, cortical-subcortical, subcortical-nonsegmental, segmental, and peripheral. Levetiracetam, valproic acid, and clonazepam are often used to treat cortical myoclonus. In cortical-subcortical myoclonus, treatment of myoclonic seizures is prioritized, valproic acid being the mainstay of therapy. Subcortical-nonsegmental myoclonus may be treated with clonazepam, though numerous agents have been used depending on the etiology. Segmental and peripheral myoclonus are often resistant to treatment, but anticonvulsants and botulinum toxin injections may be of utility depending upon the case. Pharmacological treatments are often hampered by scarce evidence-based knowledge, adverse effects, and variable efficacy of medications.

Expert consensus on clinical applications of high-frequency oscillations in epilepsy

Studies in animal models of epilepsy and pre-surgical patients have unanimously found a strong correlation between high-frequency oscillations (HFOs, > 80 Hz) and the epileptogenic zone, suggesting that HFOs can be a potential biomarker of epileptogenicity and epileptogenesis. This consensus includes the definition and standard detection techniques of HFOs, the localizing value of pathological HFOs for epileptic foci, and different ways to distinguish physiological from epileptic HFOs. The latest clinical applications of HFOs in epilepsy and the related findings are also discussed. HFOs will advance our understanding of the pathophysiology of epilepsy.

Nomenclature of Genetically Determined Myoclonus Syndromes: Recommendations of the International Parkinson and Movement Disorder Society Task Force

Genetically determined myoclonus disorders are a result of a large number of genes. They have wide clinical variation and no systematic nomenclature. With next-generation sequencing, genetic diagnostics require stringent criteria to associate genes and phenotype. To improve (future) classification and recognition of genetically determined movement disorders, the Movement Disorder Society Task Force for Nomenclature of Genetic Movement Disorders (2012) advocates and renews the naming system of locus symbols. Here, we propose a nomenclature for myoclonus syndromes and related disorders with myoclonic jerks (hyperekplexia and myoclonic epileptic encephalopathies) to guide clinicians in their diagnostic approach to patients with these disorders. Sixty-seven genes were included in the nomenclature. They were divided into 3 subgroups: prominent myoclonus syndromes, 35 genes; prominent myoclonus syndromes combined with another prominent movement disorder, 9 genes; disorders that present usually with other phenotypes but can manifest as a prominent myoclonus syndrome, 23 genes. An additional movement disorder is seen in nearly all myoclonus syndromes: ataxia (n = 41), ataxia and dystonia (n = 6), and dystonia (n = 5). However, no additional movement disorders were seen in related disorders. Cognitive decline and epilepsy are present in the vast majority. The anatomical origin of myoclonus is known in 64% of genetic disorders: cortical (n = 34), noncortical areas (n = 8), and both (n = 1). Cortical myoclonus is commonly seen in association with ataxia, and noncortical myoclonus is often seen with myoclonus-dystonia. This new nomenclature of myoclonus will guide diagnostic testing and phenotype classification. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The utility of Jerk-locked back averaging technique in diagnosis of generalized myoclonic epilepsy with normal scalp EEG: A case report

RATIONALE

The diagnosis of myoclonic epilepsy and the classification of generalized or partial type may be challenging, especially when the scalp electroencephalogram (EEG) is normal. In such situation, how to apply another electrophysiological technique to begin the diagnosis and classification? The utility of Jerk-locked back averaging technique has been described in our case.

PATIENT CONCERNS

A Chinese patient (male, 21 years old) presented with frequent unilateral or bilateral shoulder-jerking. He has an epilepsy history of complex partial seizure (CPS) or secondary tonic-clonic seizure (sGTCS) for 10 years.

DIAGNOSIS

After admission, scalp EEG was performed with the normal result when the patient showed the jerks. According to the patient's clinical presentation, we suspected myolconic seizure, but there was lack of objective evidence. Then we used Jerk-locked back averaging technique to help begin the diagnosis. A bilateral-symmetrical time-locked, evoked cortical averaging potential that preceded the jerk has been found. So the jerks were considered as cortical origin and generalized myoclonic seizure was confirmed.

INTERVENTIONS

So in this situation, we added another antiepileptic drug of Levetiracetam (1500 mg/24 h).

OUTCOMES

One week later, the jerk seizure had disappeared, and in the following visit, he had an improved prognosis with decreased seizure frequency.

LESSONS

Generalized polyspike-slow wave in EEG was common to see in myoclonic seizure and can help to make the classification. However, it should not dissuade clinicians from the diagnosis of myoclonic epilepsy with normal scalp EEG. Under this condition, we may apply other electrophysiological technique such as Jerk-locked back averaging technique, to give objective evidence to verify the cortical origin.

Acute Opioid-Induced Myoclonic Reaction after Use of Fentanyl as an Anesthetic Drug for an Emergency Cesarean Section

Myoclonus is an abnormal involuntary movement that has been previously reported with administration of high doses of opioids for prolonged periods of time. In this case, however, we report an acute myoclonic reaction and review the literature on the possible causative pathophysiology. We report the case of a 24-year-old woman who was admitted for postdated cesarean section. She started to have abnormal involuntary movements after administration of an epidural anesthesia containing 700 μg of fentanyl with 115 mL (0.5) bupivacaine and 40 mL (2%) lidocaine. Upon examination, the patient was conscious, alert, and oriented. Her vital signs were stable. Her movements can be described as generalized, sudden, involuntary, jerking movements, involving the upper limbs, head, torso as well as the lower limbs. The frequency of these jerks was about every 1–2 min lasting for 10 s. There was no change in level of consciousness during these abnormal movements. The rest of the neurological examination was normal. Laboratory values showed normoglycemia and normal serum biochemistry. A routine electroencephalogram showed no epileptiform activity. Brain imaging was normal. Based on history, examination, and laboratory findings, we made the diagnosis of drug-induced myoclonus, which in this clinical scenario was secondary to fentanyl. We discontinued fentanyl and, gradually, the intensity and frequency of the abnormal movements decreased and disappeared after a few hours. A clear definitive explanation of the acute effect of opioids is still to be reached. It involves an interaction of complex neuroanatomical pathways and neurophysiological receptors. Nonetheless, a unanimous effort is needed to raise awareness about the role of opioids in the development of abnormal movements and their clinical management, to insure that they do not go unnoticed in the clinical scenarios, and to further add more scientific content that could help in reaching an explanatory theory.

Myoclonic Disorders

Few movement disorders seem to make a straightforward approach to diagnosis and treatment more difficult and frustrating than myoclonus, due to its plethora of causes and its variable classifications. Nevertheless, in recent years, exciting advances have been made in the elucidation of the pathophysiology and genetic basis of many disorders presenting with myoclonus. Here, we provide a review of all of the important types of myoclonus encountered in pediatric and adult neurology, with an emphasis on the recent developments that have led to a deeper understanding of this intriguing phenomenon. An up-to-date list of the genetic basis of all major myoclonic disorders is presented. Randomized studies are scarce in myoclonus therapy, but helpful pragmatic approaches at diagnosis as well as treatment have been recently suggested.

Time-frequency analysis of intracranial EEG in patients with myoclonic seizures

Myoclonic seizures are defined as generalized seizures according to the classification of seizure by the International League Against Epilepsy (ILAE). The pathogenesis of myoclonic seizures is not yet clear. There are very few studies on the focal surgical treatment of myoclonic seizures. The aim of this study is to investigate the characteristics of myoclonic seizure onset in different bands of the intracranial electroencephalogram (EEG) and their dynamic changes in temporal and spatial evolution. We studied four patients with myoclonic seizures who were under the focal resection of the epileptogenic zone. We retrospectively analyzed the semiology, electrocorticogram (ECoG) and imaging data of these patients, and conducted time-frequency analysis of broadband ECoG activity. We found that myoclonic seizures without clinical lateralizing signs could be improved by the resection of the epileptogenic zone. The ECoG power in different frequency bands increased to a peak at 0.5s before the clinical seizure onset and decreased quickly afterwards. The power of alpha activity was highest during the preictal and ictal periods. The central zone had higher power than the epileptogenic zone in all frequency bands during the preictal period, but this difference was not statistically significant. Our results suggest that myoclonic seizures in some patients might have a focal origination, with a fast bilateral propagating network in all frequency bands, especially the alpha band.

Post-hypoxic Myoclonus: Current Concepts, Neurophysiology, and Treatment

Background

Myoclonus may occur after hypoxia. In 1963, Lance and Adams described persistent myoclonus with other features after hypoxia. However, myoclonus occurring immediately after hypoxia may demonstrate different syndromic features from classic Lance–Adams syndrome (LAS). The aim of this review is to provide up-to-date information about the spectrum of myoclonus occurring after hypoxia with emphasis on neurophysiological features.

Methods

A literature search was performed on PubMed database from 1960 to 2015. The following search terms were used: “myoclonus,” “post anoxic myoclonus,” “post hypoxic myoclonus,” and “Lance Adams syndrome.” The articles describing clinical features, neurophysiology, management, and prognosis of post-hypoxic myoclonus cases were included for review.

Results

Several reports in the literature were separated clinically into “acute post-hypoxic myoclonus,” which occurred within hours of severe hypoxia, and “chronic post-hypoxic myoclonus,” which occurred with some recovery of mental status as the LAS. Acute post-hypoxic myoclonus was generalized in the setting of coma. Chronic post-hypoxic myoclonus presented as multifocal cortical action myoclonus that was significantly disabling. There was overlap of neurophysiological findings for these two syndromes but also different features. Treatment options for these two distinct clinical–neurophysiologic post-hypoxic myoclonus syndromes were approached differently.

Discussion

The review of clinical and neurophysiological findings suggests that myoclonus after hypoxia manifests in one or a combination of distinct syndromes: acute and/or chronic myoclonus. The mechanism of post-hypoxic myoclonus may arise either from cortical and/or subcortical structures. More research is needed to clarify mechanisms and treatment of post-hypoxic myoclonus.

Fentanyl bolus induces muscle tremors in sevoflurane-anaesthetized piglets

Intravenous fentanyl (10 mcg/kg) or saline (control) was randomly administered to 10 healthy sevoflurane-mono-anaesthetized piglets. Trembling was assessed by two blinded observers using a visual analogue scale (VAS) and a simple ordinal scale at baseline and 5 min (T5) after drug administration. If no trembling was observed at that time point, the opposite treatment was administered and piglets were re-evaluated after another 5 min (T10). Four out of five piglets showed trembling after fentanyl (T5), while none given saline showed any trembling. With fentanyl the VAS scores were significantly higher at T5 compared either with baseline or with the control treatment. Control animals received fentanyl after the 5 min evaluation and all piglets showed clear trembling afterwards. The median time after fentanyl administration until first muscle tremors was 51 (20–840) s. In summary, nine out of 10 sevoflurane-anaesthetized piglets showed muscle tremors after intravenous fentanyl. Tremors subsided over time and no specific treatment was necessary.

Comparison of the Effects of Low-Dose Midazolam, Magnesium Sulfate, Remifentanil and Low-Dose Etomidate on Prevention of Etomidate-Induced Myoclonus in Orthopedic Surgeries

BACKGROUND

Etomidate is a potent hypnotic agent with several desirable advantages such as providing a stable cardiovascular profile with minimal respiratory adverse effects and better hemodynamic stability compared with other induction agents. This drug is associated, however, with myoclonic movements which is characterized by a sudden, brief muscle contractions as a disturbing side-effect.

OBJECTIVES

The present study was designed to compare the effectiveness of low- dose midazolam, magnesium sulfate, remifentanil and low-dose etomidate to suppress etomidate-induced myoclonus in orthopedic surgery.

PATIENTS AND METHODS

A double-blind clinical trial study was conducted in an academic hospital from September 2014 to August 2015. Two hundred and eighty-four eligible patients, American society of anesthesiologists class I - II, scheduled for elective orthopedic surgery were randomly allocated into four equal groups (n = 71). They received premedication with intravenous low-dose midazolam 0.015 mg/kg, magnesium sulfate 30 mg/kg, remifentanil 1 μg/kg and low-dose etomidate 0.03 mg/kg two minutes before induction of anesthesia with 0.3 mg/kg intravenous etomidate. Then the incidence and intensity of myoclonus were evaluated on a scale of 0 - 3; 0 = no myoclonus; 1 = mild (movement at wrist); 2 = moderate (movement at arm only, elbow or shoulder); and 3 = severe, generalized response or movement in more than one extremity, within ninety seconds. Any adverse effect due to these premedication agents was recorded.

RESULTS

The incidence and intensity of myoclonus were significantly lower in the low-dose etomidate group. The incidence rates of myoclonus were 51 (71.85%), 61 (85.9%), 30 (42.3%) and 41 (57.7%), and the percentages of patients who experienced grade III of myoclonus were 30 (58.8%), 32 (52.5%), 9 (30%) and 14 (34.1%) in the midazolam, magnesium sulfate, etomidate and remifentanil groups, respectively. The incidence and intensity of myoclonus were significantly lower in the low-dose etomidate group (P = 0.0001). No notable adverse effect was detected in our patients during the study period.

CONCLUSIONS

Intravenous etomidate 0.03 mg/kg prior to induction can effectively reduce the incidence and severity of myoclonus linked to etomidate.

Familial benign neonatal sleep myoclonus

Benign neonatal sleep myoclonus is a nonepileptic syndrome characterized by myoclonic jerks during sleep. It occurs in the first weeks of life and disappears, in most cases, within 3 months. There are no sequelae, and psychomotor and cognitive development are normal. The syndrome is usually sporadic; only a few familial cases have been reported in the literature. This case report describes three members of a single family with benign neonatal sleep myoclonus and discusses its differentiation from other types of myoclonus.

Myoclonus: current concepts and recent advances

Myoclonus presents as a sudden brief jerk caused by involuntary muscle activity. An organisational framework is crucial for determining the medical significance of the myoclonus as well as for its treatment. Clinical presentations of myoclonus are divided into physiological, essential, epileptic, and symptomatic. Most causes of myoclonus are symptomatic and include posthypoxia, toxic-metabolic disorders, reactions to drugs, storage disease, and neurodegenerative disorders. The assessment of myoclonus includes an initial screening for those causes that are common or easily corrected. If needed, further testing may include clinical neurophysiological techniques, enzyme activities, tissue biopsy, and genetic testing. The motor cortex is the most commonly shown myoclonus source, but origins from subcortical areas, brainstem, spinal, and peripheral nervous system also occur. If treatment of the underlying disorder is not possible, treatment of symptoms is worthwhile, although limited by side-effects and a lack of controlled evidence.

Rehabilitation of movement disorders11A commercial party with a direct financial interest in the results of the research supporting this article has conferred or will confer a financial benefit upon the author or one or more of the authors. Elovic is on the advisory board and speaker’s bureau of Allergan

This self-directed learning module highlights several movement disorders. These include dystonia, chorea, tremors, and myoclonus. A description of the clinical presentation and associated disease processes is presented. Although the discussion on treatment focuses on pharmacologic intervention, surgical options are presented when appropriate. Other movement disorders (ie, parkinsonism) are discussed elsewhere in the Study Guide.

OVERALL ARTICLE OBJECTIVES

(a) To define the various symptoms and etiologies of dystonia; (b) to define chorea and its treatment; (c) to define tremors, including associated neurologic disorders, plus pharmacologic and potential surgical interventions; and (d) to describe the symptoms, classification, and treatment of primary and secondary myoclonus.

Myoclonus and metabolic alkalosis from licorice in antacid

A 90-year-old woman with hypertension developed metabolic alkalosis and myoclonus. Her medications included diltiazem hydrochloride, benidipine hydrochloride, kallidinogenase, procaterol hydrochloride, sennoside, dihydrocodeine phosphate, and KM powder antacid that contained 354 mg of licorice and 900 mg of sodium bicarbonate per 3.9 g of powder. Endocrinological studies showed slightly reduced plasma renin activity and normal plasma aldosterone concentration. A provisional diagnosis of licorice-induced metabolic alkalosis was established and the patient was successfully treated after correction of serum pH and cessation of the medications. Licorice-induced metabolic alkalosis must be considered in the differential diagnosis of myoclonus.

Gait and Balance Dysfunction in Adults

Determining the precise cause of gait dysfunction in adults is often difficult because of the multifactorial nature of the disorder. Additionally, elderly patients have other comorbidities that further complicate their diagnosis. A proper history and physical examination, however, often allow the clinician to arrive at the correct diagnosis. Once a diagnosis is reached, appropriate therapeutic decisions can be made. Patients presenting with Parkinsonism need a thorough evaluation to rule out potentially reversible conditions, such as normal pressure hydrocephalus. Patients with idiopathic Parkinson's disease usually develop gait difficulty and freezing episodes late in the course of the illness. Another important cause of gait disturbance in adults is the cerebellar ataxias. Among the sporadic forms, gluten sensitivity is an important consideration. Identification of this entity is important, because the disease process can be halted with a gluten-free diet. Another group is the paraneoplastic ataxias, which can often be diagnosed in the proper clinical setting. Most of the adult-onset hereditary ataxias are autosomal dominant conditions. Except for the episodic ataxias, treatment of these conditions has been disappointing. Mixed results have been obtained with the use of amantadine, buspirone, and 5-hydroxytryptophan. Physical therapy plays an important role in the gait rehabilitation of these patients. Over the past several years, researchers have developed a greater understanding of motor control and how it relates to freezing. Clinicians can now train patients to use external cues to overcome their motor blocks. Another important advance has been the development of subthalamic nucleus deep brain stimulation in the treatment of patients with troublesome peak dose dyskinesia and other motor fluctuations. Subthalamic nucleus deep brain stimulation should be considered when best medical treatment fails. Cortical myoclonus can be treated with levetiracetam, which has US Food and Drug Administration approval as an antiepileptic agent. It has been quite effective in the treatment of myoclonus and should be considered when other medications fail.

Myoclonus and neurodegenerative disease--what's in a name?

Myoclonus is a clinical symptom (or sign) defined as sudden, brief, shock-like, involuntary movements caused by muscular contractions or inhibitions. It may be classified by examination findings, etiology, or physiological characteristics. The main physiological categories for myocolonus are cortical, cortical-subcortical, subcortical, segmental, and peripheral. Neurodegenerative syndromes are potential causes of symptomatic myoclonus. Such syndromes include multiple system atrophy, corticobasal degeneration, progressive supranuclear palsy, frontotemporal dementia and parkinsonism linked to chromosome 17, Huntington's disease, dentato-rubro-pallido-luysian atrophy, Alzheimer's disease, and Parkinson's disease, and other Lewy body disorders. Each neurodegenerative syndrome can have overlapping as well as distinctive clinical neurophysiological properties. However, claims of differentiating between neurodegenerative disorders by using the presence or absence of small amplitude distal action myclonus appear unwarranted. When the myoclonus is small and repetitive, it may not be possible to distinguish it from tremor by phenotypic appearance alone. In this case, clinical neurophysiological offers an opportunity to provide greater differentiation of the phenomenon. More study of the myoclonus in neurodegenerative disease will lead to a better understanding of the processes that cause phenotypic variability among these disorders.

A case of primary spinal myoclonus: clinical presentation and possible mechanisms involved

Spinal myoclonus is a rare movement disorder characterized by myoclonic involvement of a group of muscles supplied by a few contiguous segments of the spinal cord. Structural lesions are usually the cause, but in primary spinal myoclonus the etiology remains unknown. We present the case of a 26-year-old woman with cervical spinal myoclonus in which both clinical and electromyographic findings pointed to the segment C1-C3 as the origin of the myoclonus. Laboratorial examinations were normal and no structural lesion was found in magnetic resonance imaging (MRI). Botulinum toxin type A was injected in infrahyoid muscles and cervical paraspinal musculature. The patient remained free of symptoms for almost five months. The pathophysiology of spinal myoclonus remains speculative, but there is evidence that various possible mechanisms can be involved: loss of inhibitory function of local dorsal horn interneurons, abnormal hyperactivity of local anterior horn neurons, aberrant local axons re-excitations and loss of inhibition from suprasegmentar descending pathways.

Small-amplitude cortical myoclonus in Parkinson's disease: physiology and clinical observations

We studied the occurrence of small-amplitude myo- clonus in 20 idiopathic Parkinson's disease patients who had no evidence of dementia as defined by criteria in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition. Parkinson's disease was diagnosed by United Kingdom Brain Bank criteria, and clinical assessment was performed with the Unified Parkinson's Disease Rating Scale motor score, Hoehn and Yahr staging, and the Mini-Mental State Examination. Clinical assessment showed a range of mild-to-moderate disease severity. All patients underwent polygraphic electro-encephalographic-electromyographic (EMG) recording with back-averaging, somatosensory evoked potential testing, and attempted elicitation of long-latency EMG responses. Multichannel surface EMG recording during muscle activation showed irregular, multifocal, brief (<50 msec) myoclonus EMG discharges. Back-averaging consistently showed a focal, short-latency, electroencephalographic transient prior to the myoclonus EMG discharge. Cortical somatosensory evoked potential waves were not enlarged, and long-latency EMG responses at rest were not present. The small-amplitude myoclonus in such cases arises from an abnormal discharge from the sensorimotor cortex. The mechanism of this cortical myoclonus in Parkinson's disease has differences from the more common "cortical reflex myoclonus" physiology. Advanced parkinsonism is not a requirement for manifestation of this myoclonus type. Although the myoclonus occurred without dementia in these cases, its relationship to the subsequent development of cognitive impairment remains to be defined.

Myoclonus secondary to withdrawal from transdermal fentanyl: case report and literature review

Myoclonus is a common and well-described adverse effect of opioids. Most cases reported in the literature have been associated with opioid administration, rather than with opioid withdrawal. We describe a case of myoclonus secondary to withdrawal from transdermal fentanyl. We review the literature regarding myoclonus related to opioid therapy (opioid-induced myoclonus) and withdrawal (opioid withdrawal myoclonus), and discuss possible mechanisms and therapies for these phenomena.

Strategies to manage the adverse effects of oral morphine: an evidence-based report

Successful pain management with opioids requires that adequate analgesia be achieved without excessive adverse effects. By these criteria, a substantial minority of patients treated with oral morphine (10% to 30%) do not have a successful outcome because of (1) excessive adverse effects, (2) inadequate analgesia, or (3) a combination of both excessive adverse effects along with inadequate analgesia. The management of excessive adverse effects remains a major clinical challenge. Multiple approaches have been described to address this problem. The clinical challenge of selecting the best option is enhanced by the lack of definitive, evidence-based comparative data. Indeed, this aspect of opioid therapeutics has become a focus of substantial controversy. This study presents evidence-based recommendations for clinical-practice formulated by an Expert Working Group of the European Association of Palliative Care (EAPC) Research NETWORK: These recommendations highlight the need for careful evaluation to distinguish between morphine adverse effects from comorbidity, dehydration, or drug interactions, and initial consideration of dose reduction (possibly by the addition of a co analgesic). If side effects persist, the clinician should consider options of symptomatic management of the adverse effect, opioid rotation, or switching route of systemic administration. The approaches are described and guidelines are provided to aid in selecting between therapeutic options.

Methadone-induced myoclonus in advanced cancer

Methadone is recommended as being free of some of the neuropsychological side effects noticed with morphine, which are attributed to active metabolites. A patient that received methadone for cancer-associated pain developed myoclonus as a side effect. This has rarely been reported before in the literature. The pathophysiology and management of myoclonus are discussed.

Benign segmental myoclonus: electrophysiological evidence of transient dysfunction in the brainstem

We present a 66-year-old patient with segmental myoclonus evoked by a brainstem infarction. The myoclonus appeared soon after a cerebrovascular accident and it was evident in the soft palate, jaw, neck, shoulders and upper limbs. Brain MRI showed infarction in the left pons and left cerebellum. Small amounts of orally administered clonazepam were remarkably effective. Electroencephalogram (EEG) and auditory brainstem response (ABR) were normal. Somatosensory evoked potential (SSEP) revealed delays in P 14 and N19 recorded at C3 by right median nerve stimulation. These findings were normalized in 4 days. Seg-mental myoclonus is thought to be evoked by olivary hypertrophy following cerebrovascular accident in the brainstem and is said to be resistant to medication. The limited involvement of the brainstem in our patient may account for the transient segmental myoclonus. The prognosis for this type of segmental myoclonus is excellent.

Primary care guide to myoclonus and chorea. Characteristics, causes, and clinical options

Myoclonus and chorea are hyperkinetic movement disorders that confer a jerky appearance. Myoclonus involves a quick and simple jerk, whereas the jerking in chorea combines with other, slower movements in a continuous, flowing fashion. Both disorders have many different causes, and diagnosis requires knowledge of common clinical characteristics and directed ancillary testing. Symptomatic treatment is available, but reversal of the underlying cause should be considered first if possible. The potential benefits of treatment must be weighed against the risk of drug side effects.

Nova-1 regulates neuron-specific alternative splicing and is essential for neuronal viability

We have combined genetic and biochemical approaches to analyze the function of the RNA-binding protein Nova-1, the paraneoplastic opsoclonus-myoclonus ataxia (POMA) antigen. Nova-1 null mice die postnatally from a motor deficit associated with apoptotic death of spinal and brainstem neurons. Nova-1 null mice show specific splicing defects in two inhibitory receptor pre-mRNAs, glycine alpha2 exon 3A (GlyRalpha2 E3A) and GABA(A) exon gamma2L. Nova protein in brain extracts specifically bound to a previously identified GlyRalpha2 intronic (UCAUY)3 Nova target sequence, and Nova-1 acted directly on this element to increase E3A splicing in cotransfection assays. We conclude that Nova-1 binds RNA in a sequence-specific manner to regulate neuronal pre-mRNA alternative splicing; the defect in splicing in Nova-1 null mice provides a model for understanding the motor dysfunction in POMA.

Differentiating myoclonus from tics

A Myoclonus Versus Tic Checklist facilitates making this vexing differential diagnosis. Although it appears to be a valuable tool for clinical, educational, and research purposes, psychometric characterization of the Myoclonus Versus Tic Checklist is needed.

Electrophysiological observations in hereditary parkinsonism-dementia with Lewy body pathology

We studied the only two living affected individuals who are part of a previously reported kindred that expresses a hereditary parkinsonism-dementia syndrome with Lewy body pathology. The electrophysiological characteristics of the hyperkinetic movement disorders in these patients were examined to provide physiological insights into the clinical phenotype of this syndrome. Evaluation of both patients showed 7-9 Hz electromyographic discharges in upper extremity muscles during postural activation, and one patient showed a 4-5 Hz discharge pattern correlating to a rest tremor. Brief (<50 ms) myoclonic electromyographic discharges were seen in both patients, and a time-locked relationship to a focal cortical premovement electroencephalographic potential was elicited in one patient. Somatosensory evoked potentials were not enlarged and long latency reflexes were not enhanced. Electroencephalography was normal in one patient but showed pathologic slow frequencies in the other. The electrophysiological findings show evolution which correlates with an apparent characteristic evolution of hyperkinetic movement disorders that accompanies the severe progression of parkinsonism-dementia in this kindred. These results have implications for the future study of this and similar syndromes.

The incidence and prevalence of myoclonus in Olmsted County, Minnesota

OBJECTIVE

To study the incidence and prevalence of diagnosed myoclonus in Olmsted County, Minnesota. Little is known about the frequency and distribution of myoclonus in the general population.

DESIGN

Descriptive study with case ascertainment through a records-linkage system.

PATIENTS AND METHODS

We used a medical records-linkage system to identify all subjects whose records contained documentation of myoclonus or of diseases known to exhibit myoclonus. The records of all potential patients were reviewed by a neurologist, and only patients with pathologic and persistent myoclonus were included. Population denominators were derived from census data.

RESULTS

The average annual incidence rate of pathologic and persistent myoclonus for 1976 through 1990 was 1.3 cases per 100,000 person-years. The rate increased with advancing age and was consistently higher in men. Symptomatic myoclonus was the most common type, followed by epileptic and essential myoclonus; dementing diseases were the most common cause of symptomatic myoclonus. The lifetime prevalence of myoclonus, as of January 1, 1990, was 8.6 cases per 100,000 population, and the prevalence increased with advancing age.

CONCLUSION

Although our figures are probably under-estimated, they are the first attempt, to our knowledge, to measure myoclonus morbidity in the general population. We found clinical features and age and sex distributions different from those previously described in clinical series.

Carisoprodol-induced myoclonic encephalopathy

CASE REPORT

A 39-year-old man ingested 35 g carisoprodol. He developed agitation, tachycardia, myoclonus, and coma. The blood carisoprodol was 71 micrograms/mL; the meprobamate was 26 micrograms/mL.

DISCUSSION

Carisoprodol overdose is thought to induce simple central nervous system depression. This case demonstrates a severe overdose with symptoms more consistent with myoclonic encephalopathy. A review of cases presenting to the San Francisco Division of the California Poison Control System during 1997 suggests that carisoprodol is more commonly associated with agitation and bizarre movement disorders than the current literature suggests. The pharmacology and potential mechanisms of toxicity are discussed.

CONCLUSION

Agitation, hypertonia, and a myoclonic encephalopathy may be seen with significant carisoprodol intoxication.

Cortical myoclonus in levodopa-responsive parkinsonism

We observed myoclonic movements of the fingers and wrists in two patients with a levodopa-responsive parkinsonian syndrome most consistent with Parkinson's disease. These patients were studied with electrophysiological techniques. Brief (<50 ms) myoclonic electromyographic discharges showed a time-locked relationship to a focal premovement electroencephalographic potential. Somatosensory-evoked potentials were not enlarged and long-latency reflexes were not grossly exaggerated. This pattern of electrophysiological findings can be distinguished from those previously found in other parkinsonian syndromes. These results provide evidence for a cortical origin of the myoclonus seen in these patients.

Hemifacial spasm and other craniofacial movement disorders

Craniofacial dyskinesias encompass a variety of abnormal spontaneous craniofacial movements that often appear similar in morphology but are, in fact, of varied cause and nature. Although hemifacial spasm and blepharospasm are the two most common abnormal craniofacial movements, the clinician should be cognizant of other dyskinesias, particularly craniofacial dystonias, tremor, tic, chorea, and stereotypies. Most craniofacial dyskinesias respond favorably to injections of botulinum toxin type A or oral medications. Surgical treatment may be beneficial for refractory cases.

Cortical Myoclonus in Huntington's disease associated with an enlarged somatosensory evoked potential

We report the electrophysiologic findings of myoclonus in a patient with Huntington's disease (HD). This patient was studied postoperatively after a bilateral fetal cell transplant in his striatum. Incomplete transient improvement was seen in the myoclonus, followed by gradual deterioration. The myoclonus itself had a cortical correlate and was associated with an enlarged somatosensory evoked potential (SEP), consistent with the presence of cortical reflex myoclonus. An enlarged SEP has not been previously reported in myoclonus associated with HD. The postulated mechanisms for myoclonus, when it occurs in HD, have differed in the literature. The reason for the transient improvement of the myoclonus following transplantation is unclear, but this case raises the possibility that basal ganglia circuits may modulate cortical myoclonic activity.

Electrophysiological observations in idiopathic opsoclonus-myoclonus syndrome

To supplement existing knowledge regarding the pathophysiology of the opsoclonus-myoclonus syndrome, electrophysiological findings are reported in three patients with idiopathic opsoclonus-myoclonus. Surface electromyography (EMG) revealed < 100-ms synchronous discharges correlating with the clinical myoclonus. Short duration EMG discharges, with no back-averaged cortical correlate, normal gross electroencephalogram, and no exaggerated responses with either evoked potential testing or long latency EMG responses were observed. The clinical and electrophysiological findings we describe are consistent with a brainstem origin of the myoclonus in this syndrome, with concurrent abnormalities in cerebellar circuits, similar to those described for paraneoplastic cases. The constellation of these electrophysiological findings differentiates the myoclonus in these patients from other clinical myoclonic entities.