The following sections about reticular reflex myoclonus was excerpted from Eplilesy textbook on 2013/02/16
Reticular reflex myoclonus originates in a hyperexcitable caudal brainstem reticular formation, giving rise to a widespread pattern of muscle activation with proximal and flexor predominance, spontaneous or induced by various stimuli. The impulses may travel up the brainstem. Reticular reflex myoclonus may be present simultaneously with cortical myoclonus.
Reticular reflex myoclonus is not time-locked to EEG discharges, and the sensory evoked potentials are not enhanced. Myoclonus is triggered by stimuli, but the temporal relationship is variable between the stimuli and the myoclonus, whereas it is constant in patients with cortical reflex myoclonus. The EMG discharges start in the areas of lower cranial nerves (sternocleidomastoid muscle, trapezius muscle). They go up to the facial muscles, down to the upper limbs, then to lower limbs. Therefore, it was speculated that the stimuli excited the reticular formation and that abnormal electrical activity then spread from it to the upper brainstem and the spinal cord.
2013年2月16日 星期六
Thalamocortical myoclonus
The following sections about thalamocortical myoclonus was excerpted from Eplilesy textbook on 2013/02/16
Thalamocortical myoclonus or idiopathic generalized epileptic myoclonus represents the common type of myoclonus in various epileptic syndromes. Myoclonia are often spontaneous, predominantly arrhythmic and axial with varying severity, and associated chronologically with an EEG pattern of diffuse polyspikes or (poly) spike-and-wave discharges. A hyperexcitable cortex is thought to be driven diffusely and synchronously by ascending subcortical inputs that trigger the paroxysmal events. As a consequence, muscles from both sides are activated, and muscles innervated by the cranial nerves are involved through a rostrocaudal manner.
Electrophysiologically, SEP usually does not show giant SEP, and C-reflex may be recorded at rest. A negative peak of the generalized spike (30–100 msec duration) precedes the jerk (<100 msec duration) by 20 to 75 msec. The latency of the spike is relatively longer, and the temporal relationship is looser than in that of cortical myoclonus. The underlying mechanism of the thalamocortical myoclonus is still uncertain. The myoclonus of benign myoclonic epilepsy of infancy, myoclonic-astatic epilepsy, and JME belongs to this category.
Myoclonus observed in patients with Dravet syndrome is not straightforward: Patients may exhibit massive myoclonus combined with a generalized spike-wave (rarely in infancy, mostly in childhood), and erratic myoclonus, particularly during episodes of myoclonic status, in which the patient is drowsy with diffuse slow wave activity and few spikes. The generator remains unidentified.
Thalamocortical myoclonus or idiopathic generalized epileptic myoclonus represents the common type of myoclonus in various epileptic syndromes. Myoclonia are often spontaneous, predominantly arrhythmic and axial with varying severity, and associated chronologically with an EEG pattern of diffuse polyspikes or (poly) spike-and-wave discharges. A hyperexcitable cortex is thought to be driven diffusely and synchronously by ascending subcortical inputs that trigger the paroxysmal events. As a consequence, muscles from both sides are activated, and muscles innervated by the cranial nerves are involved through a rostrocaudal manner.
Electrophysiologically, SEP usually does not show giant SEP, and C-reflex may be recorded at rest. A negative peak of the generalized spike (30–100 msec duration) precedes the jerk (<100 msec duration) by 20 to 75 msec. The latency of the spike is relatively longer, and the temporal relationship is looser than in that of cortical myoclonus. The underlying mechanism of the thalamocortical myoclonus is still uncertain. The myoclonus of benign myoclonic epilepsy of infancy, myoclonic-astatic epilepsy, and JME belongs to this category.
Myoclonus observed in patients with Dravet syndrome is not straightforward: Patients may exhibit massive myoclonus combined with a generalized spike-wave (rarely in infancy, mostly in childhood), and erratic myoclonus, particularly during episodes of myoclonic status, in which the patient is drowsy with diffuse slow wave activity and few spikes. The generator remains unidentified.
Cortical myoclonus
The following sections about cortical myoclonus was excerpted from Eplilesy textbook on 2013/02/16
Cortical myoclonus reflects impulses that originate in the sensorimotor cortex and travel down the brainstem. Cortical myoclonus is typically seen in progressive myoclonus epilepsy. Muscles involved tend to be distal more than proximal and flexor more than extensor, and to involve more the face and upper extremities than the rest of the body. Cortical myoclonus is more commonly encountered in a multifocal form, presenting with multifocal spike discharges. If myoclonus is triggered by stimuli, the term cortical reflex myoclonus is used. If myoclonus occurs periodically, the term epilepsia partialis continua is used. The neurons in the sensorimotor cortex may be primarily hyperexcitable, or may be driven by abnormal inputs from the neurons of other brain parts. Therefore, cortical myoclonus occasionally is called fragmented epileptic convulsion.
In patients with cortical reflex myoclonus, the cortical components of median-nerve SEP showed abnormally large amplitude. Usually, the initial peaks (N20/P22) are not large, and the following components become higher. This giant SEP is thought to indicate hyperexcitability of the sensorimotor cortex. Abnormally large evoked potentials were also reported by photic stimulation.
When the peripheral nerve is stimulated, the stimulus goes up the spino-thalamo-cortical tract and, after excitation of the pyramidal neuron, it goes down the cortico-spinal tract, resulting in muscle contraction (long-loop reflex). In normal subjects, long-loop reflex can be recorded only when subjects maintain muscle contractions. In patients with cortical reflex myoclonus, however, this reflex can be recorded even while resting (C-reflex). The latency of C-reflex for median nerve stimulation is about 40 to 45 msec, which is almost double of the latency of N20 to the median nerve stimulation. When the C-reflex is recorded from the contralateral limbs to the stimuli, the latency delay is about 10 msec to the ipsilateral limbs, which corresponds to the traveling time of the transcallosal pathway. This stimulation-locked muscle contraction is believed to share the same underlying mechanism with cortical reflex myoclonus.
Some EEG correlates are time-locked to cortical myoclonus. However, because of the relatively smaller amplitude of the EEG spikes in comparison with the background activities, the physiologic correlates of myoclonus can only be detected by using jerk-locked (EEG or magnetoencephalograhic [MEG]) averaging (JLA of jerk-locked magentic field [JLF]) or coherence analysis method. In JLA, EEGs are averaged with respect to the EMG onset, to reduce the non–time locked background EEG activities. Positive peak of the EEG spikes is 15 to 20 msec prior to the myoclonus for the upper limbs, and 25 to 40 msec for the lower limbs. Spikes are located around the contralateral primary motor cortex.
As such, cortical reflex myoclonus is caused by hyperexcitability of the primary sensorimotor cortex. However, because giant SEPs are not always present in patients with cortical reflex myoclonus (as in dentatorubral-pallidoluysian atrophy [DRPLA]), some other pathophysiologic mechanisms may exist.
In Lennox-Gastaut syndrome (LGS), myoclonus is rare and disclosed only in those cases with a cortical lesion affecting the rolandic area; thus, myoclonus appears to be produced by a secondary generalization of focal cortical myoclonus. They also present with arrhythmic, distal small focal jerks, leading to the individual tiny finger movements unaccompanied by premyoclonic potentials on JLA that Wilkins et al. proposed to call minipolymyoclonus. Brown et al. indicated that the major role of facilitation of inter- and intra-hemispheric spread of cortical myoclonic activity is through trans-callosal or intrahemispheric corticocortical pathways in producing generalized or bilateral myoclonus. Therefore, bilateral jerks may not be synchronous in patients with cortical myoclonus.
Cortical myoclonus reflects impulses that originate in the sensorimotor cortex and travel down the brainstem. Cortical myoclonus is typically seen in progressive myoclonus epilepsy. Muscles involved tend to be distal more than proximal and flexor more than extensor, and to involve more the face and upper extremities than the rest of the body. Cortical myoclonus is more commonly encountered in a multifocal form, presenting with multifocal spike discharges. If myoclonus is triggered by stimuli, the term cortical reflex myoclonus is used. If myoclonus occurs periodically, the term epilepsia partialis continua is used. The neurons in the sensorimotor cortex may be primarily hyperexcitable, or may be driven by abnormal inputs from the neurons of other brain parts. Therefore, cortical myoclonus occasionally is called fragmented epileptic convulsion.
In patients with cortical reflex myoclonus, the cortical components of median-nerve SEP showed abnormally large amplitude. Usually, the initial peaks (N20/P22) are not large, and the following components become higher. This giant SEP is thought to indicate hyperexcitability of the sensorimotor cortex. Abnormally large evoked potentials were also reported by photic stimulation.
When the peripheral nerve is stimulated, the stimulus goes up the spino-thalamo-cortical tract and, after excitation of the pyramidal neuron, it goes down the cortico-spinal tract, resulting in muscle contraction (long-loop reflex). In normal subjects, long-loop reflex can be recorded only when subjects maintain muscle contractions. In patients with cortical reflex myoclonus, however, this reflex can be recorded even while resting (C-reflex). The latency of C-reflex for median nerve stimulation is about 40 to 45 msec, which is almost double of the latency of N20 to the median nerve stimulation. When the C-reflex is recorded from the contralateral limbs to the stimuli, the latency delay is about 10 msec to the ipsilateral limbs, which corresponds to the traveling time of the transcallosal pathway. This stimulation-locked muscle contraction is believed to share the same underlying mechanism with cortical reflex myoclonus.
Some EEG correlates are time-locked to cortical myoclonus. However, because of the relatively smaller amplitude of the EEG spikes in comparison with the background activities, the physiologic correlates of myoclonus can only be detected by using jerk-locked (EEG or magnetoencephalograhic [MEG]) averaging (JLA of jerk-locked magentic field [JLF]) or coherence analysis method. In JLA, EEGs are averaged with respect to the EMG onset, to reduce the non–time locked background EEG activities. Positive peak of the EEG spikes is 15 to 20 msec prior to the myoclonus for the upper limbs, and 25 to 40 msec for the lower limbs. Spikes are located around the contralateral primary motor cortex.
As such, cortical reflex myoclonus is caused by hyperexcitability of the primary sensorimotor cortex. However, because giant SEPs are not always present in patients with cortical reflex myoclonus (as in dentatorubral-pallidoluysian atrophy [DRPLA]), some other pathophysiologic mechanisms may exist.
In Lennox-Gastaut syndrome (LGS), myoclonus is rare and disclosed only in those cases with a cortical lesion affecting the rolandic area; thus, myoclonus appears to be produced by a secondary generalization of focal cortical myoclonus. They also present with arrhythmic, distal small focal jerks, leading to the individual tiny finger movements unaccompanied by premyoclonic potentials on JLA that Wilkins et al. proposed to call minipolymyoclonus. Brown et al. indicated that the major role of facilitation of inter- and intra-hemispheric spread of cortical myoclonic activity is through trans-callosal or intrahemispheric corticocortical pathways in producing generalized or bilateral myoclonus. Therefore, bilateral jerks may not be synchronous in patients with cortical myoclonus.
Stereotypies
The following paragraph was taken from textbook "Neurology and clinical neuroscience" on 2013/02/05:
Stereotypies are repetitive, rhythmical, and invariant motor behaviors, without an apparent purpose or function, that can vary from simple motor behaviors such as rocking or hand waving to extraordinarily complex acts and rituals. They are one of the defining features of autism and are common in patients with mental retardation. Stereotypies are seen in adults with lesions or disorders affecting the frontostriatal circuit running between the dorsolateral frontal cortex and the head of the caudate nucleus. Frontotemporal dementias commonly manifest with stereotypic behaviors resulting from degeneration of the dorsolateral prefrontal cortex. Stimulant medications can produce complex stereotypies through a dopaminergic effect on the basal ganglia. Other repetitive motor behaviors such as compulsive behaviors and tics are seen in patients with Gilles de la Tourette syndrome and obsessive-compulsive disorder, both of which are considered to be associated with basal ganglia pathology. Of importance is that stereotypies, compulsions, complex tics, mannerisms (unusual or pathological styles of performing goal-directed activities, such as a bizarre gait and unusual ways of greeting people), and habits can often be difficult to distinguish purely on the basis of subjective observation. The context and history of the motor phenomena provide important diagnostic information.
Stereotypies are repetitive, rhythmical, and invariant motor behaviors, without an apparent purpose or function, that can vary from simple motor behaviors such as rocking or hand waving to extraordinarily complex acts and rituals. They are one of the defining features of autism and are common in patients with mental retardation. Stereotypies are seen in adults with lesions or disorders affecting the frontostriatal circuit running between the dorsolateral frontal cortex and the head of the caudate nucleus. Frontotemporal dementias commonly manifest with stereotypic behaviors resulting from degeneration of the dorsolateral prefrontal cortex. Stimulant medications can produce complex stereotypies through a dopaminergic effect on the basal ganglia. Other repetitive motor behaviors such as compulsive behaviors and tics are seen in patients with Gilles de la Tourette syndrome and obsessive-compulsive disorder, both of which are considered to be associated with basal ganglia pathology. Of importance is that stereotypies, compulsions, complex tics, mannerisms (unusual or pathological styles of performing goal-directed activities, such as a bizarre gait and unusual ways of greeting people), and habits can often be difficult to distinguish purely on the basis of subjective observation. The context and history of the motor phenomena provide important diagnostic information.
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