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Query: UMLS:C0027066 (myoclonus)
 4,275 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Negative myoclonus is an involuntary movement produced by a short interruption of muscle contraction. In this paper, recent concepts, pathomechanisms and treatment in negative myoclonus are reviewed. Two patients with negative myoclonus are also presented. One is an 18-year-old girl with Gaucher disease, and the other is a 14-year-old boy with simple partial motor epilepsy. Electrical silent period was demonstrated when negative myoclonus was clinically observed. In both patients, somatosensory evoked potentials showed giant responses, which may indicate that mechanisms of negative myoclonus have a relationship with cortical abnormal excitability.
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PMID:[Negative myoclonus]. 827 82

We present the first documented case of photic-induced epileptic negative myoclonus. A 17-year-old girl had experienced two generalized tonic-clonic seizures (GTCS) while watching television. The only EEG abnormality was a photoparoxysmal response (PPR), which was sometimes accompanied by loss of postural tone in both arms. Valproate was effective in abolishing photosensitivity. Negative myoclonus should be included among the ictal phenomena accompanying PPR.
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PMID:Photic-induced epileptic negative myoclonus: a case report. 861 79

Negative myoclonus (NM) is a motor phenomenon characterized by involuntary jerky movements due to a brief, sudden interruption of muscular activity. This motor disturbance can be observed in a variety of clinical conditions, that can range from physiological NM, occurring when falling asleep or after prolonged exercise, to asterixis, a form of NM observed in patients with toxic-metabolic encephalopathies or with focal brain lesions, or, as a paroxysmal phenomenon, labelled as epileptic negative myoclonus, in epileptic patients. Neurophysiological investigations are essential to diagnose NM and to distinguish it from other motor disorders, such as tremor or positive myoclonus. Furthermore, neurophysiological findings can provide useful information supporting a subcortical or cortical origin of NM. In cortical NM, recent data suggest a role of cortical active inhibitory areas in the generation of this motor phenomenon.
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PMID:Negative myoclonus. 889 93

Sudden and brief involuntary movements of central nervous system (CNS) origin called myoclonus may be cortical (motor strip), thalamocortical (thalamocortical loop) or reticular (caudal reticular formation). Epileptic, cortical and thalamocortical myoclonus are combined with a spike which, when it is focal, needs back-averaging to be demonstrated. Negative myoclonus due to lapse of tone can only be demonstrated during antigravidic posture and may be combined with either a slow wave or the second, positive component of a polyspike-wave. Epileptic myoclonus must be distinguished from epileptic spasms and tonic seizures, and from non-epileptic myoclonus, tics, tremor and chorea. Myoclonus may occur in partial symptomatic (mainly Rasmussen and dysplasia), cryptogenic (frontal) or idiopathic (negative myoclonus in CSWS) epilepsy. Generalized myoclonus is part of inborn errors of metabolism, non-progressive encephalopathy (mainly Angelman) and idiopathic epilepsy (juvenile and infantile benign and severe forms, and myoclonic-astatic epilepsy). Carbamazepine, vigabatrin and eventually lamotrigine may worsen myoclonus whereas it may be improved by benzodiazepines, valproate, lamotrigine, zonisamide and piracetam according to etiology. Pathophysiology must take in account maturation processes, lesions and genetic predisposition. However, precise mechanisms remain unknown and only hypotheses can be proposed, that could clarify the age-related EEG and clinical expression of the various syndromes.
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PMID:Myoclonus and epilepsy in childhood: 1996 Royaumont meeting. 960 May 41

Negative myoclonus, commonly known as asterixis, is often observed in patients with toxic-metabolic encephalopathies or focal brain lesions. It is a movement disorder characterized by postural lapses resulting from brief cessation of tonic muscular contraction. Negative myoclonus has a characteristic appearance on needle electromyography. Lapses in continuous postural muscle activity can lead to falls. This increased risk of falls makes it particularly important to recognize and treat negative myoclonus, especially in patients with multiple medical problems, deconditioning, and gait disturbances. To our knowledge, there have been no published reports implicating negative myoclonus as a cause of falls in adults. We present a case of asterixis as a cause of falls and near falls in a patient with metastatic breast cancer and normal mental status who was receiving gabapentin.
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PMID:Asterixis related to gabapentin as a cause of falls. 1614 53

Negative myoclonus (NM) is a motor disorder characterized by a sudden and abrupt interruption of muscular activity. The EMG correlate of NM is a brief (<500 ms) silent period (SP) not preceded by any enhancement of EMG activity (i.e. myoclonus). This study investigated the role of premotor cortex (PMC), primary motor cortex (MI), primary somatosensory area (SI) and supplementary motor area (SMA) in the pathophysiology of cortical NM by means of intracerebral low frequency (1 Hz) electrical stimulation. In three drug-resistant epileptic patients undergoing presurgical evaluation, we delivered single electric pulses (stimulus duration: 3 ms; stimulus intensity ranging from 0.4 to 3 mA) to PMC (2 patients), MI (1 patient), SI and SMA through stereo-EEG electrodes; surface EMG was collected from both deltoids. The results showed that (i) the stimulation of PMC or MI could evoke a motor evoked potential (MEP) either at rest or during contraction, in this latter case followed by an SP; however, in two patients, at the lowest stimulus intensities (0.4 mA), 50% of stimuli could induce a pure SP, i.e. not preceded by an MEP; raising the intensity of stimulation (0.6 mA), the SPs showed an antecedent MEP in >80% of stimuli; (ii) the stimulation of SI at low stimulus intensities (from 0.4 to 0.8 mA) induced in two patients only SPs, never associated with an antecedent MEP, whereas in the third subject the SPs could be inconstantly preceded by an MEP; by incrementing the stimulus intensity (up to 3 mA), in all three patients the SPs tended to be preceded, although not constantly, by an MEP; stimulus intensity affected SP duration (i.e. the higher the intensity, the longer the SP), without influencing the latency of onset of the SPs; (iii) the stimulation of SMA induced only pure SPs, at all stimulus intensities up to 3 mA; as for SI, increment of stimulus intensity was paralleled by an increase in SP duration, without influencing the onset latency of SPs. We conclude that single electric pulse stimulation of PMC, MI, SI and SMA through stereo-EEG electrodes can induce pure SPs, not preceded by an MEP, which clinically appear as NM, suggesting therefore that these cortical areas may be involved in the genesis of this motor phenomenon. However, it must be pointed out that SMA stimulation induced only pure SPs, regardless of the stimulus intensity, whereas occurrence of pure SPs following stimulation of PMC, MI, and SI depended mainly on the intensity of stimulation.
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PMID:Negative myoclonus induced by cortical electrical stimulation in epileptic patients. 1627 66

Negative myoclonus (NM) is an unspecific motor disorder that can characterize a variety of neurological conditions. From the clinical point of view, NM appears as a shock-like involuntary jerky movement caused by a sudden, brief interruption of muscle activity. Asterixis is a type of NM that occurs typically in toxic-metabolic encephalopathies. NM of epileptic nature, or epileptic negative myoclonus (ENM), is defined as an interruption of tonic muscle activity, which is time-locked to an epileptic EEG abnormality, without evidence of an antecedent positive myoclonia in the agonist-antagonist muscles. ENM can be observed in idiopathic, cryptogenic, and symptomatic epileptic disorders. Pathophysiological hypotheses on the origin of NM involve subcortical as well as cortical mechanisms. Recent neuroimaging and neurophysiologic investigations, including intracerebral recordings and electrical stimulation procedures in epileptic patients, suggest the participation of premotor, primary motor, primary sensory, and supplementary motor areas in the genesis of NM. Polygraphic monitoring is essential for the diagnosis of NM, allowing the demonstration of brief interruptions of a tonic EMG activity, not preceded by a positive myoclonus in the agonist and antagonist muscles of the affected limb. Simultaneous EEG-EMG monitoring demonstrating the association of NM with an epileptic potential is consistent with the diagnosis of ENM. Evolution and prognosis of NM is mainly related to aetiology. In childhood idiopathic partial epilepsy, ENM can respond to some drugs (in particular, ethosuximide), whereas other medications (such as carbamazepine or phenytoin) have been reported to induce or worsen it.
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PMID:Negative myoclonus. An overview of its clinical features, pathophysiological mechanisms, and management. 1733 79