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PubMed1986

Electroencephalographic correlates of myoclonus.

Fifty-five consecutive cases of myoclonus owing to various etiologies were studied by conventional EEG-EMG polygraphic recordings and/or jerk-locked or back averaging. The technique of back-averaging was shown to be useful not only for detecting EEG correlates of myoclonus that are not recognizable on the routine polygraph but also for investigating the temporal and topographic relationship between the EEG activities and myoclonus. Thirteen of 17 cases of PME and related disorders, in whom back-averaging and SEP were studied, were shown to have both a myoclonus-related cortical spike over the contralateral central area, preceding the myoclonus of an upper extremity by 6 to 22 msec, and a giant SEP accompanied by an enhanced C reflex. In these cases of "cortical reflex myoclonus," the myoclonus-related spike was similar to the P25-N33 components of the giant SEP in its wave form, scalp topography, temporal relationship to myoclonus or to C reflex, succeeding cortical excitability, and drug effect. All of this suggests participation of common physiological mechanisms in those two activities. In two cases of PME, in which myoclonus involved bilateral proximal muscles synchronously, the myoclonus-related spike was maximal near the vertex, and there was no giant SEP. The significance of this subgroup remains undetermined. In six cases of the PME group, back-averaging was inapplicable because of rare occurrence of myoclonus, but they showed a typical giant SEP accompanied by an enhanced C reflex. In CJD, back-averaging demonstrated a sharp wave or PSD over the contralateral hemisphere, preceding the myoclonus by 50 to 85 msec. This form of myoclonus seems to be subcortical in origin. In essential myoclonus and oculopalatal-somatic myoclonus, there was neither myoclonus-related cortical spike nor giant SEP. Electrical stimulation of the peripheral nerve at variable intervals after the myoclonus onset (jerk-locked-SEP paradigm) was shown to be useful for investigating the influence of myoclonus on cortical excitability.

Brain Diseases, Metabolic↗
PubMed1990

Myoclonus: analysis of monoamine, GABA, and other systems.

Myoclonus is a clinical term meaning a quick involuntary jerk, seen in normal subjects under certain circumstances, including sleep, and in certain disease states. It is important as a symptom that may impair function and as an indicator of neurological dysfunction. Not until patients with myoclonus and major functional disability were reported in the 1960s was attention given to understanding its basis and pharmacotherapy. Reports of myoclonus developing after anoxic brain injury, and its response to treatment with the serotonin precursor 5-hydroxytryptophan (5-HTP), drew special attention. Further experience showed that only a few patients with myoclonus benefit from 5-HTP therapy. Benzodiazepines (BDZs) are often helpful in the treatment of myoclonus. Their beneficial effects decline with chronic administration because of drug tolerance, and the theoretical basis for BDZ responses remains unclear. The relationships between myoclonus, clonus, and epilepsy are discussed, as is the possible contribution of slow signaling transmembrane receptors to synchronization of motoneuron firing, which is suggested as a hallmark of myoclonus. Myoclonus may originate in many CNS sites, but the brain-stem reticular formation is especially relevant to myoclonus. Brain-stem serotonin neurons have special influence on spinal motoneurons, on startle responses, and on myoclonus. Among 5-HT receptors, 5-HT1A receptors are related to some forms of myoclonus, although 5-HT2 receptors are also implicated. GABAA receptors are related to some forms of myoclonus. Blockade of GABAA receptors or GABA synthesis regularly evokes convulsive seizures, but administration of many GABA agonists and some GABA uptake blockers paradoxically may evoke myoclonus. Injection of GABA receptor blockers into some brain areas has anticonvulsant effects. Stimulation of GABAA receptors may therefore promote or antagonize myoclonus depending on which GABA receptors are involved, the state of the system, etc. The role of glycine receptors is well established in some animal models, but has yet to be clearly established for human myoclonus. Opiates may produce myoclonus when given intrathecally or in high dosage. The concept of excitant anesthetics and special function of certain GABA receptors is discussed.

Animals↗
PubMed1998

Electrophysiological study of myoclonus in pediatric practice.

Myoclonus can be caused from a variety of central nervous system disorders. With regard to its pathophysiology, much work has been done in adult patients, but reports from pediatric clinics are scarce. We describe the clinical and electrophysiological features of four different types of myoclonus in children using back averaging technique. In a patient with cortical reflex myoclonus, myoclonic jerks were induced in the distal right arm by taps on the ipsilateral fingers. Myoclonus was preceded by the cortical spike which was localized posterior to the central sulcus contralateral to the myoclonus, and the cortical spike was time-locked to the myoclonus. In a patient with subcortico-cortical myoclonus, myoclonus occurred as a focal motor seizure. Myoclonic jerks were preceded by generalized cortical waves which were of maximal amplitude over the cortex contralateral to the myoclonus, and cortical waves time-locked to the myoclonus. A patient with spinal myoclonus had rhythmical and segmental myoclonus. Myoclonus was induced in both arms after electrical stimulation at the wrist with a latency which was slightly longer than that of the F wave. In a patient with brainstem myoclonus, muscle activity was bilaterally synchronous and was predominant in the proximal flexors. The pattern of muscle recruitment suggested that the myoclonus signal travelled downward along the spinal cord and upward through the brainstem. The back averaging technique is essential in the differential diagnosis of myoclonus.

Adolescent↗
PubMed1997

Focal subcortical reflex myoclonus. A clinical and neurophysiological study.

BACKGROUND: Patients with progressive myoclonus epilepsy or progressive myoclonus ataxia often show a focal myoclonus, both spontaneous and reflex to somatosensory stimuli. Myoclonus is time-locked to large ("giant") electroencephalographic potentials. Previous authors have classified it as a "cortical reflex myoclonus," with the assumption that it invariably arises from an abnormal corticifugal neuron discharge. OBJECTIVE: To identify the myoclonus source, using various neurophysiological techniques, in 5 patients with progressive myoclonus epilepsy/ataxia. METHODS: Extensive investigations were performed to ascertain the clinical diagnosis. Electrophysiologically, the main method was transcranial cortical stimulation and motor evoked potential measurement. The latency and amplitude of the spontaneous myoclonus and the premyoclonus cortical spike, the reflex myoclonus (C-reflex), and the giant somatosensory evoked potential were also analyzed. The behavior of giant somatosensory evoked potentials and C-reflexes were then studied on single, consecutive trials. Finally, the central motor pathway excitability and its changes attributable to a prior somatosensory input were determined. RESULTS: The motor evoked potential studies showed that the expected corticomuscular conduction time (23 milliseconds) of the myoclonic electromyographic potential was longer than that previously suspected. Considering this, the premyoclonus cortical spike and the giant somatosensory evoked potential were so close to the spontaneous/reflex jerks that they could not reflect a cortical myoclonus source. In 4 patients, the C-reflex latency (< 41.6 milliseconds) was shorter than that often reported in previous studies. The giant somatosensory evoked potential and the C-reflex showed no simple cause-effect link. Motor pathways were hyperexcitable only in response to somatosensory inputs. CONCLUSIONS: The data pointed to a cortical myoclonus origin only in the patient whose C-reflex had the longest latency (44 milliseconds). In the remaining patients, a subcortical source was far more likely. In this group of patients, cortical stimulation disclosed a new myoclonus variety, for which the term focal subcortical reflex myoclonus is proposed; it mimics cortical reflex myoclonus but has a shorter latency.

Action Potentials↗
PubMed1992

Electrophysiological and pharmacological studies of somatosensory reflex myoclonus.

Reflex myoclonus displays symptomatological heterogeneity involving the cortical and brain stem types that seem to originate above the spinal cord. Three cases of generalized myoclonus proved to be spontaneous and stimulus-sensitive, and increased with action. Segmental spinal myoclonus was spontaneous, stimulus-sensitive and rhythmical and decreased with action. Two cases of post-anoxic myoclonus seemed to be of the reticular reflex in which myoclonus was manifested in all muscles, particularly the proximal ones, and for which the EEG showed no spikes preceding myoclonus. The evoked electromyogram showed a long-loop reflex (LLR) of high amplitude, with no giant somatosensory evoked potential (SEP). Pharmacological examinations showed that the thyrotropin-releasing hormone (TRH) enhanced the onset of myoclonus, shortened the latency of the LLR and increased its amplitude, but caused no remarkable changes in SEP. These results indicate that TRH stimulates the medullary reticular neuron, thereby enhancing reticular reflex myoclonus. The myoclonus of a 3rd case was believed to be cortical reflex myoclonus on the basis of the emergence of giant SEP, increased LLR and the onset of spikes in the EEGs preceding myoclonic jerks, as ascertained by jerk-locked averaging analysis with muscular discharge. Pharmacologically, LLR, SEP and myoclonus showed no definite changes in response to TRH. Segmental myoclonus which seemed to have a spinal origin, showed no giant SEP, enhanced LLR or cortical spikes in the electrophysiological studies. No definite clinical or electrophysiological changes in response to TRH were observed. We believe the TRH administration test may be useful in the differential diagnosis of stimulus-sensitive myoclonus. In addition, the origins and nature of these types of reflex myoclonus are discussed.

Acoustic Stimulation↗
PubMed1986

5-HT-mediated myoclonus in the guinea pig as a model of brainstem 5-HT and tryptamine receptor action.

Indoleamine-induced myoclonus in guinea pigs is a specific model of brainstem 5-HT function that can be used to characterize the indoleamine systems initiating myoclonus. 5-HT precursors and indole-containing 5-HT agonists induce myoclonus in guinea pigs, but piperazine-containing compounds do not. This selectivity of action correlates with the ability of 5-HT agonists to act at 5-HT-1 receptors. Further evidence for the involvement of a brainstem 5-HT receptor subpopulation in the initiation of myoclonus is shown by the differential ability of 5-HT antagonists to inhibit 5-HTP-induced myoclonus and of 5-HT reuptake blockers to potentiate threshold myoclonus. Distinct tryptamine receptors also may be involved in producing myoclonus, since indoleamine antagonists show differing potencies in inhibiting 5-HTP- and tryptamine-induced myoclonus. Tryptamine-induced myoclonus is, however, dependent on intact presynaptic 5-HT function. Biochemical studies indicate that 5-HT is primarily responsible for 5-HTP-evoked myoclonus, whereas tryptamine predominates in tryptamine-induced myoclonus. Both 5-HT and tryptamine may contribute to myoclonus produced by L-tryptophan. Indoleamine-induced myoclonus in guinea pigs may be valuable in studying the organization of brainstem indoleamine systems that may be involved in some forms of human myoclonus.

5-Hydroxytryptophan↗
PubMed2003

Cortical myoclonus during lithium exposure.

BACKGROUND: Myoclonus can occur in association with lithium therapy at toxic and therapeutic dosages, and can be a predominant and disabling adverse effect. Moreover, myoclonus has been reported when lithium has been combined with cyclic antidepressants and with the neuroleptic clozapine. Although clinical case reports exist, no electrophysiologic data are available that provide a source or a neurophysiological mechanism for the myoclonus seen in lithium therapy. OBJECTIVE: To describe the electrophysiologic characteristics and source of the myoclonus associated with lithium therapy. DESIGN AND METHODS: We retrospectively analyzed 5 cases of myoclonus during lithium therapy. We reviewed the clinical features and results of previous electrophysiologic testing. Four patients received lithium monotherapy; and 1, sertraline hydrochloride and nefazodone hydrochloride in addition to lithium. The electrophysiologic data that had been gathered included multichannel surface electromyographic (EMG) recordings with simultaneous electroencephalography (EEG), somatosensory evoked potentials, and elicitation of long-latency EMG reflexes to median and digital nerve stimulation. RESULTS: All 5 patients showed multifocal action myoclonus without reflex activation and only rare occurrence at rest. In each case, back-averaging created a focal EEG transient over the contralateral sensorimotor area preceding the myoclonus EMG discharge. In 2 of the patients receiving lithium monotherapy, the therapy was discontinued and the myoclonus disappeared. CONCLUSIONS: Lithium, by itself, can be associated with prominent clinical myoclonus, short-duration (<50-millisecond) myoclonus EMG discharges and cortical action myoclonus without the presence of epileptiform abnormalities on the routine EEG. This myoclonus is different from the most common form that is well documented to occur with tricyclic antidepressant therapy by clinical and electrophysiologic means.

Adult↗
PubMed1991

Hereditary essential myoclonus in a large Norwegian family.

We examined 56 members of a large Norwegian family with hereditary essential myoclonus, affecting mainly the neck and upper parts of the body, and inherited in an autosomal-dominant pattern. We observed definite myoclonus in nine individuals, probable myoclonus in one, and possible myoclonus in one. There were two other living members who had a history compatible with myoclonus but who had developed a permanent remission, so we did not observe the movements, and two who had involuntary movements only with stress. Writing usually increased the myoclonus in the neck and trunk, but did not produce myoclonus in the arm used for writing. Having a conversation with an individual who was aware of being watched would also usually increase the myoclonus. Alcohol ameliorated the myoclonus in many, but not all, affected members. Activities such as walking and concentrating during reading would usually reduce the myoclonus. Three living members with definite myoclonus also had features of mild focal dystonia, either spasmodic torticollis or blepharospasm, indicating that focal dystonia may exist as part of the clinical spectrum in hereditary essential myoclonus. In addition to examining the members of the family, we videotaped them and obtained blood samples for molecular genetic analysis.

Adolescent↗
PubMed1986

Stimulus-sensitive myoclonus of the baboon Papio papio: pharmacological studies reveal interactions between benzodiazepines and the central cholinergic system.

The baboon Papio papio develops a nonepileptic myoclonus 20 to 30 min after i.m. benzodiazepine injection. It is characterized by bilateral jerks involving mainly the neck and the trunk, by the absence of any correlative EEG paroxysmal discharge, and by its facilitation during movement or agitation. This myoclonus resembles the intention myoclonus of human patients as seen, for example, after anoxia. We found in experiments on 10 adolescent baboons that atropine alone induced the myoclonus for several hours, that physostigmine completely antagonized the benzodiazepine-induced as well as the atropine-induced myoclonus, and that the peripherally acting cholinergic antagonist, methyl-QNB, and agonist prostigmine had no action on the myoclonus, suggesting that the benzodiazepine-induced myoclonus in this species depends on a strong depression of the central cholinergic system by benzodiazepine. The benzodiazepine-induced myoclonus was mediated by benzodiazepine receptors as it was blocked by the specific benzodiazepine receptor antagonist, Ro 15-1788, which did not block atropine-induced myoclonus; latency to myoclonus after benzodiazepine was longer than after atropine. These facts suggest that benzodiazepines, by an as yet unknown mechanism, induce a depression of the cholinergic system which in turn leads to the development of myoclonus. Finally, the benzodiazepine-induced myoclonus of the baboon can be considered as a good model for testing drugs that act on the muscarinic cholinergic system and also for testing benzodiazepine-acetylcholine interactions.

Animals↗