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

The method of magnetic transcranial stimulation of the motor cortex produces both excitatory and inhibitory effect. Definition of excitability and inhibitory threshold represents clinically useful indicator. In order to reduce variability of the thresholds, it is important to notice mental activity, posture, type of magnetic stimulator, involuntary movement, muscle tonus and age. Excitability threshold was elevated in patients with stroke and reduced in patients with epilepsy. Enhancement of motor excitability by subthreshold magnetic stimulation of the motor cortex prior to voluntary movement was observed during simple reaction time measurement. Reaction time can be divided into a period of resting condition and the premotion facilitatory effect in the 50 approximately 60 ms after the target stimuli. In patients with Parkinson's disease, the prolongation of reaction time is due to a prolongation of a period of premotion facilitatory effect. Jerk-locked MEP is a useful technique to evaluate a change of motor excitability after voluntary or involuntary movement. To record jerk-locked MEP, magnetic stimulation of the motor cortex is delivered at varying intervals after the onset of the EMG activity. We classified the cortical reflex myoclonus into three forms according to changes of motor excitability after C reflex.
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PMID:[Analysis of cortical excitation and inhibition using transcranial magnetic stimulation]. 875 48

We conducted electrophysiological studies in two Asian patients with probable corticobasal degeneration (CBD). The duration of illness from onset was 16 and 20 months, respectively. The clinical manifestations were markedly asymmetric and characterized by cortical sensory loss, apraxia, action myoclonus, action tremor, and akinetic-rigid parkinsonism. Neither patient responded to levodopa therapy. Simple photon-emission computed tomography (SPECT) study showed significantly decreased regional cerebral blood flow in the frontoparietal areas and thalamus opposite to the predominantly affected limb. A series of electrophysiological studies failed to identify giant somatosensory evoked potentials (SEPs), enhanced long latency electromyography (EMG) reflex, and cortical spikes preceding myoclonic jerk. However, the earliest cortical component of the median nerve SEP was exclusively enlarged in one patient and preserved with depression of the subsequent components in the other patient. Significantly shorter postmotor-evoked potential (MEP) silent period was found after the transcranial magnetic stimulation of the motor cortex in both patients. CBD is a unique clinical entity characterized by action myoclonus probably the result of the pathologic hyperexcitability of the motor cortex, based on a loss of inhibitory input from the sensory cortex.
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PMID:Electrophysiological studies of early stage corticobasal degeneration. 945 39

A single case study of a 58 year-old male with right asymmetric apraxia and akinetic-rigid syndrome is described. Brainimaging scans (MRI, SPECT) indicated asymmetric cortical atrophy compatible with the diagnosis of Corticobasal Degeneration. Reflex myoclonus was absent and myoclonic discharges only appeared in response to pharmacological treatment of limb dystonia and rigidity. Electromyographic evidence of jerky movements was recorded only in the affected right hand and forearm after muscle relaxation, and myoclonus was not preceded by an EEG paroxysm. The cortical components of the correspondent SEPs were not increased in amplitude while LLRs recordings showed a late response over the muscles of the affected side. Furthermore, the duration of post MEP silent period was bilaterally reduced. This single case study report points out that sometimes myoclonus in Corticobasal Degeneration can be masked by the presence of increased muscle tone.
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PMID:Masked myoclonus in corticobasal degeneration: neurophysiological study of a case. 1185 Oct 11

We investigated the association between clinical and neurophysiological characteristics in patients with a clinical diagnosis of probable corticobasal degeneration (CBD), and searched for neurophysiological features supporting the diagnosis in life. Ten patients with clinically probable CBD underwent comprehensive neurological evaluation and brain MRI. Long latency reflexes (LLR), upper limb somatosensory (SEP) and motor evoked (MEP) potentials were recorded. The mini-mental state examination (MMSE), the phonemic verbal fluency test (PVFT) and the De Renzi ideomotor apraxia test were also performed. Polygraphic EEG was performed in the six patients with myoclonus. The SEP N30 frontal component was absent bilaterally in four patients, was absent on the left side in one, and had increased latency in other three. MEPs were abnormal in four patients (three had prolonged central motor conduction time, one of whom also had increased MEP threshold, and one had increased MEP threshold). All six patients with myoclonus had enhanced LLRs at rest, which were also of abnormally increased amplitude during motor activation; latencies were generally shorter than in classic cortical reflex myoclonus. On back-averaging, no EEG spikes time-locked to EMG activity were found in any myoclonus patient. Five patients were demented by MMSE, eight had ideomotor apraxia scores in the ideomotor apraxia range and five had defective verbal fluency. Brain MRI revealed asymmetric cortical atrophy in all patients, particularly evident frontoparietally. Neurophysiological techniques, particularly LLR, can assist CBD diagnosis especially in patients with myoclonus. Patients with evident parkinsonism had greater SEP N30 (frontal) abnormalities, while most patients with marked paresis had slower MEP times.
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PMID:Neurophysiological features in relation to clinical signs in clinically diagnosed corticobasal degeneration. 1275 52