Sinal myoclonus.

A 5-year-old boy is reported with spinal myoclonus caused by cervical astrocytoma due to neurofibromatosis. The essential clinical and electromyographical signs of spinal myoclonus are the following: (1) Continuous rhythmical appearance in muscles innervated by the affected segments of the spinal cord. (2) Synchronous myoclonus in muscles innervated by the same spinal segments of one body side, asynchronous myoclonus in muscles of different segments as well as in contralateral muscles of the same segments. (3) Usually stable frequency, which may increase to a manifold under the influence of different stimuli. (4) Accentuation of the myoclonus under mental distress, disappearance during deeper sleep. The pathophysiological basis of spinal myoclonus might be a disinhibition in the area of the spinal formatio reticularis. Supraspinal stimuli can influence the myoclonus.     

Brachial plexus myoclonus.

Rhythmic myoclonus in an arm began abruptly following an injury and persisted continuously for six years. Topographical EMG showed abnormal activity confined to muscles innervated by the axillary and radial nerves from the posterior cord of the brachial plexus. Abduction of the arm above horizontal level stopped myoclonus and EMG discharges. EEG was normal. It is suggested that the myoclonus was caused by mechanical irritation of the posterior cord of the brachial plexus.     

Cannabis-induced propriospinal myoclonus.

We report on a case of a 25-year-old woman with clusters of myoclonus induced by a single exposure to inhaled cannabis. Investigations excluded a structural abnormality of the spine. Multi-channel surface EMG with parallel frontal EEG recording confirmed the diagnosis of propriospinal myoclonus.     

Epileptic palatal myoclonus.

Palatal myoclonus (PM) is usually caused by lesions of the brainstem. We report a case of PM of focal cortical origin in a patient with epilepsia partialis continua. The PM sometimes occurred in isolation, and at other times was accompanied by unilateral face, neck, and arm twitching. This was documented by both EEG and SPECT.     

Stimulus-sensitive spinal myoclonus.

Two cases of spinal myoclonus are described; in both patients myoclonus was responsive to stimuli and absent during sleep. The first patient was considered to have viral neuronitis and the condition resolved spontaneously. The second patient had spinal cord ischaemia; there was electro-physiological evidence of abnormal alpha motor neurone activity and histological study of the spinal cord revealed a severe reduction in small and intermediate neurones. This supports the theory that spinal myoclonus may result from abnormal activity of alpha motor neurones released from control by spinal internuncial neurones.     

Gaze-evoked brainstem myoclonus.

The clinical and electrophysiological aspects of a case where brainstem reticular reflex myoclonus was related to an enlarging pontine lesion are described. It had the unusual characteristic of being evoked by sustained up gaze and left gaze.     

Electroencephalographic studies myoclonus.

Electroencephalographic studies were carried out in 30 patients with various kinds of myoclonus. It was confirmed that the technique of jerk-locked averaging with a backward averaging program was useful for detecting cortical spikes in association with the spontaneously occurring myoclonus, which are not recognized on the convential polygraph, and for evaluating the temporal and topographical relationship between the spike and the myoclonus. By this technique, cortical spikes were shown to precede the myoclonus of a contralateral upper extremity muscle by 7 to 15 ms ith progressive myoclonic epilepsy showed a high amplitude somatosensory evoked potential (SEP) in response to electrical stimulation of the median nerve. The N33 component of this high amplitude SEP was found to be similar to the myoclonus-related cortical spike in their wave form, time relationship and topographical distribution, suggesting an involvement of similar physiological mechanisms in the genesis of both phenomena. Myoclonus in these patients is compatible with "pyramidal" or "cortical loop reflex" type.     

Bulbar myoclonus without palatal myoclonus. A hypothesis on pathophysiology

A 40-year-old woman with myoclonic contractions bilaterally in the infrahyoid neck muscles, especially in the left cricothyroid muscle, was presented and successfully treated with botulinum toxin injections. The patient had a wide, aberrant vessel curving into the left dorsolateral reticular formation of the medulla oblongata. Based on our observations, we propose that symptomatic bulbar and palatal myoclonus is caused by pathology in the dorsolateral reticular formation, and not by inferior olivary dysfunction as is currently thought.     

Carbidopa/levodopa-responsive myoclonus.

A 64-year-old right-handed woman's right hand and arm developed spontaneous jerks that eventually involved her trunk. As she had some features of parkinsonism, she was treated with carbidopa/levodopa and her myoclonus dramatically improved. The mechanism accounting for this improvement is unknown.     

Benign neonatal sleep myoclonus.

Benign neonatal sleep myoclonus is a non-epileptic disorder. This phenomenon of the first weeks of life is characterized by erratic myoclonic jerks occurring only during sleep and with no electroencephalographic changes. It is not associated with perinatal complications, disappears spontaneously within two to four months, and it does not compromise future development. We illustrate with a video this relatively frequent condition, which is often misdiagnosed as epileptic in nature, and discuss the clinical characteristics and differential diagnosis.     

Cortical activity-associated negative myoclonus.

A patient with myoclonus epilepsy had 2 types of negative myoclonus as well as positive myoclonus at rest. One type followed a large EMG discharge at the end of continuous contraction and the other did not. Both types of negative myoclonus and positive myoclonus were preceded by EEG activity, predominantly distributed in the contralateral central region. It is suggested that an abnormal activity around the motor cortex suppresses a voluntary contraction as well as induces myoclonus. Clonazepam was markedly effective on both positive and negative myoclonus.     

Electroencephalographic correlates of myoclonus.

In order to overcome various drawbacks of the conventional polygraphic study of a relationship between myoclonus and EEG, the EEG preceding and following the myoclonic jerk was simultaneously averaged by the CNV program. The subjects were 7 patients presenting with myoclonus of various kinds. The conventional polygraphs showed various paroxysmal EEG activities in 4 patients, but none of those paroxysmal activities was temporally related to myoclonus except for one case. As a result of the present averaging technique, 2 patients with cerebellar ataxia with intention myoclonus showed myoclonus-related EEG spikes or spike-and-slow-waves in the contralateral central or centroparietal region. These myoclonus-related spikes preceded the myoclonus by 10-17 msec, suggesting the presence of a discharging focus in the deep cerebral structures, rather than in the cerebral cortex, in these cases. Two other patients, one with resting myoclonus and the other with postural myoclonus, showed myoclonus-related slow waves on the contralateral hemisphere. This previously undescribed method of averaged polygraphic recording will be very useful in detecting an EEG correlate of spontaneously occurring myoclonus.     

Progressive familial myoclonus epilepsy.

Seven cases of progressive familial myoclonus epilepsy occurring in three families are presented. The patients were in different stages of the illness. The EEG was abnormal in all. It is suggested that these cases belong clinically to the Lafora bodies group. Nystagmus and optic atrophy, seen in one patient, have not been described previously. Myoclonic jerks did not respond to treatment with diazepam and ethosuximide.     

Neurophysiological classification of myoclonus.

Myoclonus can be diagnosed and classified mainly based on clinical features. Neurophysiologic studies help confirm clinical diagnosis and classification, and understand underlying physiological mechanisms. The neurophysiologic classification of myoclonus is mainly based on surface EMG (individual EMG patterns, muscle spatial distribution and time sequence of muscle activation), EEG, EEG/EMG relationships (jerk-locked back-averaging, cortico-muscular coherence), somatosensory evoked potentials, and long-loop reflexes. Paired stimulation evoked response/long loop reflex and jerk-locked evoked responses evaluate the excitability changes of the primary somatosensory cortex. Transcranial magnetic stimulation can evaluate the excitability state of the primary motor cortex.     

Palatal myoclonus in postinfectious opsoclonus myoclonus syndrome : a case report.

An adult male presenting with acute onset opsoclonus, myoclonus and cerebellar ataxia is being reported. Patient had myoclonus involving limbs and palate. There are only a few reported cases associated with palatal myoclonus. Patient showed gradual spontaneous recovery. Possibility of underlying malignancy was excluded by detailed investigations.     

Reticular reflex myoclonus: a physiological type of human post-hypoxic myoclonus.

A patient with post-hypoxic myoclonus, sensitive to therapy with 5-hydroxytryptophan and clonazepam, was subjected to detailed electrophysiological investigation. Brief generalised jerks followed the critical stimulus of muscle stretch. The electroencephalogram showed generalised spikes that were associated with, but not time locked to, the myoclonus. The cranial nerve nuclei were activated upward. Analysis of the findings suggests that the mechanism of the myoclonus is hyperactivity of a reflex mediated in the reticular formation of the medulla oblongata.