Synchronous positive and negative myoclonus due to pontine hemorrhage

Negative myoclonus. An overview of its clinical features, pathophysiological mechanisms, and management

Negative myoclonus (NM) is an unspecific motor disorder that can characterize a variety of neurological conditions. From the clinical point of view, NM appears as a shock-like involuntary jerky movement caused by a sudden, brief interruption of muscle activity. Asterixis is a type of NM that occurs typically in toxic-metabolic encephalopathies. NM of epileptic nature, or epileptic negative myoclonus (ENM), is defined as an interruption of tonic muscle activity, which is time-locked to an epileptic EEG abnormality, without evidence of an antecedent positive myoclonia in the agonist-antagonist muscles. ENM can be observed in idiopathic, cryptogenic, and symptomatic epileptic disorders. Pathophysiological hypotheses on the origin of NM involve subcortical as well as cortical mechanisms. Recent neuroimaging and neurophysiologic investigations, including intracerebral recordings and electrical stimulation procedures in epileptic patients, suggest the participation of premotor, primary motor, primary sensory, and supplementary motor areas in the genesis of NM. Polygraphic monitoring is essential for the diagnosis of NM, allowing the demonstration of brief interruptions of a tonic EMG activity, not preceded by a positive myoclonus in the agonist and antagonist muscles of the affected limb. Simultaneous EEG-EMG monitoring demonstrating the association of NM with an epileptic potential is consistent with the diagnosis of ENM. Evolution and prognosis of NM is mainly related to aetiology. In childhood idiopathic partial epilepsy, ENM can respond to some drugs (in particular, ethosuximide), whereas other medications (such as carbamazepine or phenytoin) have been reported to induce or worsen it.

Influence of Mastication and Salivation on Swallowing in Stroke Patients

OBJECTIVE

To determine differences of the oral swallowing functions between stroke and normal subjects and to identify those factors affecting dysphagia of stroke patients.

DESIGN

Case-control study.

SETTING

University hospital.

PARTICIPANTS

Ten stroke and 10 healthy subjects.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Resting saliva flow rate, the total number of chews, and the duration of the oral phase until onset of pharyngeal swallow, and food viscosities both before and after the oral phase using diluted barium, pudding, thick rice gruel, and curd type yogurt.

RESULTS

The viscosity of all test foods was significantly reduced after the oral phase in both groups (P<.01). Resting saliva flow rate and the viscosity of thick rice gruel after the oral phase in the stroke group were significantly lower than in the control group (P<.01). However, there were no differences in the viscosities of the other foods between both groups. And a longer oral phase and a greater number of chews prior to pharyngeal swallow were revealed in the stroke group than in the control group (P<.01).

CONCLUSIONS

This study shows that the food requiring mastication demands a longer oral phase and a greater number of chews, and has more altered rheologic characteristics during the oral phase in stroke patients. These findings suggest that masticatory function is impaired in stroke patients, which may contribute to their swallowing dysfunction.

Increased neuronal nitric oxide synthase (nNOS) activity triggers picrotoxin-induced seizures in rats and evidence for participation of nNOS mechanism in the action of antiepileptic drugs

Increased neuronal nitric oxide synthase (nNOS) activity was observed during the prodromal period of seizures in various rat brain regions following administration of GABA(A) receptor antagonist, picrotoxin (PCT). Pretreatment with the selective nNOS inhibitor 7-nitroindazole (7-NI), dose- and time-dependently delayed the onset of clonus with a corresponding decrease in nNOS activity. The threshold dose of antiepileptic drugs (AEDs; diazepam, phenobarbitone and gabapentin) have potentiated the anticonvulsant action by pretreatment with graded doses of 7-NI. The increase in efficacy of anticonvulsant action correlated with a corresponding decrease of PCT-evoked increase in nNOS activity. The present data support a role for abnormal nNOS activity in mechanisms that trigger seizures and suggest a possible NO-mediated interplay between GABA(A) and glutamate receptors. The results of the present study provide evidence for a trigger role of neuronally produced NO in epileptogenesis induced by PCT and the participation of nNOS inhibitory mechanisms in the action of AEDs.

Benign segmental myoclonus: electrophysiological evidence of transient dysfunction in the brainstem

We present a 66-year-old patient with segmental myoclonus evoked by a brainstem infarction. The myoclonus appeared soon after a cerebrovascular accident and it was evident in the soft palate, jaw, neck, shoulders and upper limbs. Brain MRI showed infarction in the left pons and left cerebellum. Small amounts of orally administered clonazepam were remarkably effective. Electroencephalogram (EEG) and auditory brainstem response (ABR) were normal. Somatosensory evoked potential (SSEP) revealed delays in P 14 and N19 recorded at C3 by right median nerve stimulation. These findings were normalized in 4 days. Seg-mental myoclonus is thought to be evoked by olivary hypertrophy following cerebrovascular accident in the brainstem and is said to be resistant to medication. The limited involvement of the brainstem in our patient may account for the transient segmental myoclonus. The prognosis for this type of segmental myoclonus is excellent.

Neurophysiology of positive and negative myoclonus

Myoclonus is defined as a sudden, brief, jerky, shock-like, involuntary movement, arising from the central nervous system that can be caused by a muscular contraction, i.e. positive myoclonus, or by an interruption of muscular activity, i.e. negative myoclonus. Myoclonus can characterize a variety of neurological disorders, and often both positive and negative myoclonus can coexist. In this paper, we outline some relevant clinical aspects and neurophysiological features of the different types of myoclonus, with particular emphasis on the physiological findings. Indeed, since most myoclonus depend on enhancement of neuronal activities which are inherently present in normal subjects, electrophysiological studies are useful for elucidating the underlying pathophysiological mechanisms and for establishing the correct diagnosis [corrected].

Brainstem-mediated locomotion and myoclonic jerks. I. Neural substrates

Eleven of 40 decerebrated cats were found to exhibit periods of spontaneous or sensory myoclonus and locomotion beginning 24 h after decerebration. Histological analysis showed that the cats generating myoclonus hemorrhagic lesions in the retrorubral nucleus (RRN) and ventral mesopontine junction (vMPJ). However, with intact RRN and vMPJ never showed myoclonus. To verify that the lesions were responsible for myoclonus, 6 additional cats received N-methyl-D-aspartate (NMDA, 0.5 M/0.5 microliter) injections in the areas of RRN and vMPJ to produce bilateral lesions. Coordinated rhythmic leg movement (locomotion) or myoclonic twitches developed in all of these cats beginning 3 hours after NMDA injection. These NMDA lesion-induced movements appeared either spontaneously (5 out of 6 cats) or after sensory stimulation (1 cat). Four cats received saline control injections in the RRN and vMPJ and did not have spontaneous, or sensory stimulation-induced, myoclonic twitches during the 48 h observation period. These results indicate that the RRN and vMPJ have a suppressive effect on myoclonic twitches and rhythmic leg movement. Dysfunction of these regions could release motor activity into sleep and waking states.