Myoclonic attacks induced by L-dopa and bromocryptin in Parkinson patients: a sleep EEG study

Clinical neurophysiology of Parkinson's disease and parkinsonism

•

This review is part of the series on the clinical neurophysiology of movement disorders and focuses on Parkinson’s disease and parkinsonism.

•

The pathophysiology of cardinal parkinsonian motor symptoms and myoclonus are reviewed.

•

The recordings from microelectrode and deep brain stimulation electrodes are reported in detail.

This review is part of the series on the clinical neurophysiology of movement disorders. It focuses on Parkinson’s disease and parkinsonism. The topics covered include the pathophysiology of tremor, rigidity and bradykinesia, balance and gait disturbance and myoclonus in Parkinson’s disease. The use of electroencephalography, electromyography, long latency reflexes, cutaneous silent period, studies of cortical excitability with single and paired transcranial magnetic stimulation, studies of plasticity, intraoperative microelectrode recordings and recording of local field potentials from deep brain stimulation, and electrocorticography are also reviewed. In addition to advancing knowledge of pathophysiology, neurophysiological studies can be useful in refining the diagnosis, localization of surgical targets, and help to develop novel therapies for Parkinson’s disease.

The clinical heterogeneity of drug-induced myoclonus: an illustrated review

A wide variety of drugs can cause myoclonus. To illustrate this, we first discuss two personally observed cases, one presenting with generalized, but facial-predominant, myoclonus that was induced by amantadine; and the other presenting with propriospinal myoclonus triggered by an antibiotic. We then review the literature on drugs that may cause myoclonus, extracting the corresponding clinical phenotype and suggested underlying pathophysiology. The most frequently reported classes of drugs causing myoclonus include opiates, antidepressants, antipsychotics, and antibiotics. The distribution of myoclonus ranges from focal to generalized, even amongst patients using the same drug, which suggests various neuro-anatomical generators. Possible underlying pathophysiological alterations involve serotonin, dopamine, GABA, and glutamate-related processes at various levels of the neuraxis. The high number of cases of drug-induced myoclonus, together with their reported heterogeneous clinical characteristics, underscores the importance of considering drugs as a possible cause of myoclonus, regardless of its clinical characteristics.

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.

Myoclonus and extrapyramidal diseases

Parkinsonism or dystonia are associated with myoclonus in several extrapyramidal diseases. Although the latter symptom is not always prominent, stimulus-sensitive, distal, or focal reflex myoclonus is frequently observed. This review will consider the clinical and electrophysiological features of myoclonus in Parkinson's disease, multiple system atrophy, corticobasal degeneration, progressive supranuclear palsy, Huntington's disease, dentatorubral-pallidoluysian atrophy, Lewy body dementia, and myoclonus with dystonia. The evidence of a long-latency reflex response, the presence of giant somatosensory evoked potentials, and the demonstration of a back-averaged premyoclonus focal cortical EEG activity often lead to classify myoclonus as a cortical phenomenon. However, a subcortical origin cannot always be ruled out.

Drug-induced myoclonus: a French pharmacovigilance database study

Various drugs have been reported to induce myoclonus. However, this adverse event is not well known because of the difficult diagnosis and the lack of pharmaco-epidemiological or controlled studies. As far as we know, there are only case reports. In the literature, antiparkinsonian medications, antipsychotics, antidepressants, anesthetics, opiates and anti-infectious drugs have been reported in the occurrence of myoclonus. In a French pharmacovigilance database study, only 423 reports (0.2%) involved drug-induced myoclonus. The median age of patients was 55 years and 10% of these patients had a concomitant neurological disease. Only 16% of these reports had a strong imputability score (likely). The most frequently involved drugs were anti-infectious (15%), antidepressants (15%), anxiolytics (14%), and opiates agents (12%). Fifty-six percent of these reports were classified as serious adverse event. Concerning outcome, most patients (84%) recovered without sequels.

Drug-induced myoclonus: frequency, mechanisms and management

Myoclonus is a sudden, abrupt, brief, 'shock-like' involuntary movement caused by muscular contractions ('positive myoclonus') or a sudden brief lapse of muscle contraction in active postural muscles ('negative myoclonus' or 'asterixis'). Various disorders can cause myoclonus including neurodegenerative and systemic metabolic disorders and CNS infections. In addition, myoclonus has been described as an adverse effect of some drugs. Level II evidence is available to indicate that levodopa, cyclic antidepressants and bismuth salts can cause myoclonus, while there is less robust evidence to associate numerous other drugs with the induction of myoclonus. The pharmacological mechanisms responsible for this adverse effect are not well established, although increased serotonergic transmission may be involved in the induction of myoclonus by several drugs. Drug-induced myoclonus usually resolves after withdrawal of the offending drug, but in some cases specific treatments are needed.

[Myoclonus in the adult: diagnostic approach]

Myoclonus, defined as shock-like involuntary movement, may be physiological or caused by a very wide variety of hereditary and acquired conditions. Because myoclonus can originate from different disorders and lesions affecting quite varied levels of the central and peripheral nervous systems, it represents from many points of view a diagnostic challenge. Moreover, new entities have been recently individualized, such as cortical tremor, which deserve renewed attention. The aim of this review is to propose a rationale for a diagnostic approach based on clinical and electrophysiological grounds. In this setting, we successively address 1) the clinical features allowing a positive diagnosis of myoclonus; 2) the clinical clues to the etiology; 3) the relevance of the clinical context to the diagnosis; and 4) the contribution of neurophysiology. Differentiating myoclonus from tics, spasm, chorea and dystonia can be difficult, and a careful reappraisal of clinical features allowing precise identification is presented. Moreover, the topographical distribution of myoclonus, the temporal pattern of muscle recruitment, the condition of occurrence and the rhythm of the event, may provide clinical clues relevant to the diagnosis. Myoclonus without associated epilepsy, myoclonus with epilepsy, myoclonus with encephalopathy, parkinsonism and/or dementia represent overlapping clinical categories, although they remain useful for the diagnostic approach. Using electrophysiology (including back-averaging EEG, MEG, SEP, C-reflex studies) to determine the origin of myoclonus may not allow us to focus on the underlying condition. Indeed, in many instances, the myoclonus is cortical in origin, but the pathology is found elsewhere.

Clinical correlates of 6-hydroxydopamine injections into A11 dopaminergic neurons in rats: a possible model for restless legs syndrome

Pursuant to the clinical suspicion that restless legs syndrome (RLS) may involve dopaminergic diencephalic spinal neurons (A11), we performed stereotaxic bilateral 6-hydroxydopamine (6-OHDA) lesions into the A11 nucleus to observe for any behavioral correlates similar to this clinical condition. Pathologic examination demonstrated a 54% reduction in A11 tyrosine hydroxylase staining cells in rats injected with 6-OHDA versus sham treatment. Multiple blindly rated 90-120-minute video epochs demonstrated an increased average number of standing episodes (14.4+/-11.7 versus 7.3+/-5.5 episodes/epoch) and increased total standing time (38.9+/-20.5 versus 25.3+/-12.2 minutes/epoch) but similar total sleep time in four lesioned rats when compared with two sham rats. Treatment of the lesioned rats with intramuscular pramipexole subsequently resulted in fewer standing episodes (4.4+/-3.3 versus 14.4+/-11.7 episodes/epoch) and less total standing time (20.9+/-12.3 versus 38.9+/-20.5 minutes/epoch) when compared with untreated lesioned rats. Despite a large number of observations, the small number of lesioned animals precluded formal statistical analysis. These behaviors are consistent, although not specific, with what would be expected in an animal model of RLS.

Myoclonus and seizures in a patient with parkinsonism: induction by levodopa and its confirmation on SEPs

A 68-year-old woman with parkinsonism showed cortical myoclonus and seizures under antiparkinsonian medication. Myoclonus was induced and enhanced by L-dopa, developing into generalized seizures. EEG was abnormal and somatosensory-evoked potentials (SEPs) showed giant SEPs, transcortical reflex (C reflex) and jerk locked potentials. Myoclonus and seizures disappeared after discontinuation of L-dopa and the introduction of valproate sodium (VPA). We described the occurrence of L-dopa-induced myoclonus and seizures in a case of parkinsonism with its SEPs findings.

Antidepressant withdrawal-induced activation (hypomania and mania): mechanism and theoretical significance

Electrocortical and behavioral arousal are separate phenomena subserved by different neural substrata operating in parallel. A comprehensive theory of 'activation' must take into account the relationships between the electrical and behavioral activating systems. In pathological or experimentally induced states paradoxes, resolvable by a theory positing functional interaction between these systems, arise. EEG arousal is directly mediated, in both the waking and sleeping state, by cholinergic mechanisms. Antidepressant withdrawal precipitates cholinergic overdrive; this would account for the apparent disturbances of REM sleep occurring when antidepressants are stopped. Generally, cholinergic overdrive would produce behavioral inhibition but in particular instances it triggers marked psychomotor arousal by mobilizing a 'limbic activating system'. The existence of a monoaminergic 'limbic activating system', system 'A', with the properties attributed to it in this paper, is supported by both clinical and laboratory observations. System 'A' theory provides a parsimonious means of adequately explaining many phenomena. This theory also has in its favor explanatory power and scope. The Cholinergic-Monoaminergic Interaction Theory of antidepressant withdrawal induced activation and of rapidly-cycling manic-depressive illness maintains that system 'A' and a cholinergic inhibitory system interact dynamically, and that excessive monoaminergic function can precipitate excessive cholinergic function and a dearth of monoaminergic function (due to autoregulation) and hence depression. Likewise, excessive cholinergic function is posited to activate monoaminergic systems and hence to secondarily cause behavioral activation. Rapidly-cycling manic-depressive patients, according to the model, develop alternating cholinergic and monoaminergic overdrive states because the homeostatic mechanisms which should serve to maintain, within normal limits, the composite of cholinergic inhibitory and monoaminergic activating influences are defective. Consequently, rather than reaching a reasonable balance compatible with adaptive function there is oscillation between extremes. Each oscillatory movement is actually a move towards the 'golden mean' and is induced by deviation from this ideal but the defective homeostatic mechanisms promote ' perpetual ' overshooting. Lithium and ECT may be useful in the treatment of rapidly-cycling patients as both treatments may down-regulate muscarinic receptors, and otherwise modify cholinergic and monoaminergic systems in ways promoting homeostasis.(ABSTRACT TRUNCATED AT 400 WORDS)

Bromocriptine and its use in Parkinsonism

Bromocriptine is a potent dopamine agonist which directly stimulates dopamine receptors. In the corpus striatum, this action results in alleviation of many of the signs and symptoms of parkinsonism. The effectiveness of bromocriptine may persist for at least one to two years; results of more prolonged treatment are not available. Adverse reactions are common and often severe, but safety in dosages up to 100 mg daily for one to two years has been adequately established. Bromocriptine is qualitatively and quantitatively similar to levodopa in both beneficial and adverse effect. However, because of variations in individual response, bromocriptine sometimes ameliorates the problems of prolonged levodopa therapy, i.e., declining efficacy, fluctuations in therapeutic response, and the development of disabling abnormal involuntary movements, Thus bromocriptine is a valuable adjunct in the treatment of parkinsonism.