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

ENM is an etiologically heterogeneous disorder clinically evident as brief (less than 500 msec) lapses of tonic muscular contraction which seems to be related to lesions or dysfunction of different anatomofunctional levels of the CNS (Fig. 13). ENM can occur in heterogeneous epileptic disorders, ranging from benign syndromic conditions (such as BECTS) to focal static lesional epilepsy, as in neuronal migration disorders, and even to severe static or progressive myoclonic encephalopathies (PMEs). Neurophysiological studies in patients with ENM lead to the following conclusions: 1. A cortical origin of ENM is supported by EEG mapping and dipole analysis of spikes related to the ENM. In particular, our data suggest that the focal spike is a paroxysmal event involving, primarily or secondarily, the centroparietal and frontal "supplementary" motor areas. 2. A cortical inhibitory active mechanism for the genesis of ENM is supported by the occurrence of a decreased motor response to TMS, with preserved spinal excitability as demonstrated by the persistence of F waves. A "cortical motor outflow inhibition" related to spike-and-wave discharges was suggested by Gloor in his Lennox lecture (34). The cortical reflex negative myoclonus, described by Shibasaki et al. (16) in PME, is also consistent with a cortical active inhibitory mechanism. The spike associated with ENM raises new issues about the definition of "interictal" versus "ictal" EEG paroxysmal activity. A single spike on the EEG can be clinically silent (therefore, "interictal") or clinically evident as ENM (then viewed as "ictal"), depending on whether a given group of muscles is at rest or is showing tonic activity (see Fig. 4). These data, from a more general perspective, imply that the motor manifestation related to EEG paroxysmal events can depend not only on amplitude, topography, or intracortical distribution of seizure activity (35), but also on plasticity (36) and on the functional condition of the motor system (37). The variability of latency between the spike and the onset of the muscular inhibition (ranging from 15 to 50 msec, for the upper limbs), and the variability of duration of the ENM itself (from 50 to 400, or more, msec) indicate that ENM could be the result of inhibitory phenomena arising not only from a single cortical "inhibitory" area, but also from subcortical and pontine structures, as discussed by Mori et al. (this volume). The neurophysiological distinction between ENM and postmyoclonic periods of muscular suppression, mainly related to an EGG slow wave, as described by Lance and Adams (2) in the postanoxic action myoclonus is still a matter of discussion (38, 39). This is also the case for other movement disorders combining action myoclonus and epilepsy-as described in Ramsay Hunt syndrome (30), now better referred to as Unverricht-Lundborg syndrome (40) (Fig. 14). In these conditions, myoclonia and muscular silent periods are inconstantly associated with paroxysmal EEG discharges, suggesting a possible thalamocortical mechanism rather than a purely cortical one. In the most prolonged muscular inhibitions, both cortical and thalamocortical mechanisms might be implicated. Clearly, our knowledge of ENM is still very limited and gaining further insights into this complex phenomenon is a challenging problem.
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PMID:Epileptic negative myoclonus. 884 69

Cortical myoclonus is a distinct clinical condition that can be defined electrophysiologically, and occurs in both children and adults. It is well known that patients sometimes exhibit stimulus-sensitive jerks and giant somatosensory-evoked potentials (SEPs). In contrast, imaging abnormalities are less prominent in many patients. Reports focusing on cortical myoclonus, except for epilepsia partialis continua, in childhood have been limited in Japan. One reason for this could be that Japanese pediatric neurologists are not familiar with the backaveraging technique. We describe the clinical and physiological features of cortical myoclonus in ten children. Routine EEG, EEG backaveraging, SEP measurement, CT/MRI (computed tomography/magnetic resonance imaging), and TMS (transcranial magnetic stimulation) were performed. All patients exhibited clear evidence of cortical myoclonus. In six patients, backaveraging was necessary since spikes were absent on routine EEG. A cortical source of the myoclonus was further supported by a TMS study performed on four patients. The etiologies of the myoclonus were diverse, cerebrovascular disease being the most common (three patients). Stimulus-sensitive or action-induced jerks were observed in three patients. Cortical SEPs were enlarged in one patient, and reduced or absent in six. Lesions were found on CT/MRI in nine patients, in five of whom the margin of the lesion was within, or adjacent to, the sensorimotor cortex. Complete destruction of the sensorimotor cortex was not observed. It was suggested that cortical neurons in the vicinity of a lesion, rather than in the lesion itself, play a role in the generation of focal myoclonus.
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PMID:Cortical myoclonus in children. 1268 95

Juvenile myclonic epilepsy (JME) can be firmly diagnosed by a careful interview of the patient focusing on the seizures and by the EEG with the help, if necessary, of long-term video-EEG monitoring using sleep and/or sleep deprivation. Background activity is normal. The interictal EEG shows diffuse or generalized spike-wave (SW) and polyspike-wave (PSW) discharges. In some patients, non-specific changes or misleading features such as focal changes are found. Changes are mostly seen at sleep onset and at awakening. Provoked awakenings are more likely to activate interictal paroxysmal abnormalities than spontaneous awakenings. The presence of a photoparoxysmal response with or without myoclonic jerks (MJ) is common (30% of the cases). Myoclonic jerks are associated with a discharge of fast, irregular, generalized PSWs that predominate anteriorly. Myoclonic jerks appear to be associated with rhythmic EEG (spike) potentials at around 20Hz. These frequencies are in the range of movement-related fast sensorimotor cortex physiological rhythms. The application of jerk-locked averaging technique has provided findings consistent with a cortical origin of MJ. Paired TMS (transcranial magnetic stimulation) studies showed a defective intracortical inhibition, due to impaired GABA-A mediated mechanisms. In this review, we present the EEG characteristics of JME with particular emphasis on the pathophysiology of MJ and on the role of sleep deprivation on interictal and ictal changes.
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PMID:Neurophysiology of juvenile myoclonic epilepsy. 2375 77