Hyperkinesia refers to an increase in muscular activity that can result in excessive abnormal movements, excessive normal movements, or a combination of both. Hyperkinesia is a state of excessive restlessness which is featured in a large variety of disorders that affect the ability to control motor movement, such as Huntington's disease. It is the opposite of hypokinesia, which refers to decreased bodily movement, as commonly manifested in Parkinson's disease.
Many hyperkinetic movements are the result of improper regulation of the basal ganglia–thalamocortical circuitry. Overactivity of a direct pathway combined with decreased activity of indirect pathway results in activation of thalamic neurons and excitation of cortical neurons, resulting in increased motor output. Many hyperkinetic disorders are psychological in nature and are typically prominent in childhood.
Classification
thumb|[[Hyperglycemia-induced involuntary movements (hemichorea and bilateral dystonia) in a 62-year-old Japanese woman with type 1 diabetes.]]
Basic hyperkinetic movements can be defined as any unwanted, excess movement. Hyperkinesia is a defining feature of many childhood movement disorders, yet distinctly differs from both hypertonia and negative signs, which are also typically involved in such disorders.
Athetosis
Athetosis is defined as a slow, continuous, involuntary writhing movement that prevents the individual from maintaining a stable posture. These are smooth, nonrhythmic movements that appear random and are not composed of any recognizable sub-movements. They mainly involve the distal extremities, but can also involve the face, neck, and trunk. Athetosis can occur in the resting state, as well as in conjunction with chorea and dystonia. When combined with chorea, as in cerebral palsy, the term "choreoathetosis" is frequently used.
Hemifacial spasm
Hemifacial spasm (HFS) is characterized by involuntary contraction of facial muscles, typically occurring only on one side of the face. Like blepharospasm, the frequency of contractions in hemifacial spasm may range from intermittent to frequent and constant. The unilateral blepharospasm of HFS may interfere with routine tasks such as driving. In addition to medication, patients may respond well to treatment with Botox. HFS may be due to vascular compression of the nerves going to the muscles of the face. For these patients, surgical decompression may be a viable option for the improvement of symptoms.
Pathophysiology
thumb|The [[basal ganglia are involved in hyperkinesia.]]
The causes of the majority of the above hyperkinetic movements can be traced to improper modulation of the basal ganglia by the subthalamic nucleus. In many cases, the excitatory output of the subthalamic nucleus is reduced, leading to a reduced inhibitory outflow of the basal ganglia. Without the normal restraining influence of the basal ganglia, upper motor neurons of the circuit tend to become more readily activated by inappropriate signals, resulting in the characteristic abnormal movements.
There are two pathways involving basal ganglia-thalamocortical circuitry, both of which originate in the neostriatum. The direct pathway projects to the internal globus pallidus (GPi) and to the substantia nigra pars reticulata (SNr). These projections are inhibitory and have been found to utilize both GABA and substance P. The indirect pathway, which projects to the globus pallidus external (GPe), is also inhibitory and uses GABA and enkephalin. The GPe projects to the subthalamic nucleus (STN), which then projects back to the GPi and GPe via excitatory, glutaminergic pathways. Excitation of the direct pathway leads to disinhibition of the GABAergic neurons of the GPi/SNr, ultimately resulting in activation of thalamic neurons and excitation of cortical neurons. In contrast, activation of the indirect pathway stimulates the inhibitory striatal GABA/enkephalin projection, resulting in suppression of GABAergic neuronal activity. This, in turn, causes disinhibition of the STN excitatory outputs, thus triggering the GPi/SNr inhibitory projections to the thalamus and decreased activation of cortical neurons. While deregulation of either of these pathways can disturb motor output, hyperkinesia is thought to result from overactivity of the direct pathway and decreased activity from the indirect pathway.
Hyperkinesia occurs when dopamine receptors, and norepinephrine receptors to a lesser extent, within the cortex and the brainstem are more sensitive to dopamine or when the dopaminergic receptors/neurons are hyperactive. Hyperkinesia can be caused by a large number of different diseases including metabolic disorders, endocrine disorders, heritable disorders, vascular disorders, or traumatic disorders. Other causes include toxins within the brain, autoimmune disease, and infections, which include meningitis.
Since the basal ganglia often have many connections with the frontal lobe of the brain, hyperkinesia can be associated with neurobehavioral or neuropsychiatric disorders such as mood changes, psychosis, anxiety, disinhibition, cognitive impairments, and inappropriate behavior.
Diagnosis
Definition
There are various terms which refer to specific movement mechanisms that contribute to the differential diagnoses of hyperkinetic disorders.
As defined by Hogan and Sternad, "posture" is a nonzero time period during which bodily movement is minimal. When a movement is called "discrete," it means that a new posture is assumed without any other postures interrupting the process. "Rhythmic" movements are those that occur in cycles of similar movements. "Repetitive," "recurrent," and "reciprocal" movements feature a certain bodily or joint position that occur more than once in a period, but not necessarily in a cyclic manner.
The disease is characterized further by the gradual onset of defects in behavior and cognition, including dementia and speech impediments, beginning in the fourth or fifth decades of life. Death usually occurs within 10–20 years after a progressive worsening of symptoms. Caused by the Huntington gene, the disease eventually contributes to selective atrophy of the Caudate nucleus and Putamen, especially of GABAergic and acetylcholinergic neurons, with some additional degeneration of the frontal and temporal cortices of the brain. The disrupted signaling in the basal ganglia network is thought to cause the hyperkinesia. There is no known cure for Huntington's disease, yet there is treatment available to minimize the hyperkinetic movements. Dopamine blockers, such as haloperidol, tetrabenazine, and amantadine, are often effective in this regard.
Wilson's disease
thumb|[[Samuel Alexander Kinnier Wilson, the neurologist most known for his description of what came to be known as Wilson's disease.]]
Wilson's disease (WD) is a rare inherited disorder in which patients have a problem metabolizing copper. In patients with WD, copper accumulates in the liver and other parts of the body, particularly the brain, eyes and kidneys. Upon accumulation in the brain, patients may experience speech problems, incoordination, swallowing problems, and prominent hyperkinetic symptoms including tremor, dystonia, and gait difficulties. Psychiatric disturbances such as irritability, impulsiveness, aggressiveness, and mood disturbances are also common.
Post-stroke repercussions
A multitude of movement disorders have been observed after either ischemic or hemorrhagic stroke. Some examples include athetosis, chorea with or without hemiballismus, tremor, dystonia, and segmental or focal myoclonus, although the prevalence of these manifestations after stroke is quite low. The amount of time that passes between stroke event and presentation of hyperkinesia depends on the type of hyperkinetic movement since their pathologies slightly differ. Chorea tends to affect older stroke survivors while dystonia tends to affect younger ones. Men and women have an equal chance of developing the hyperkinetic movements after stroke. Strokes causing small, deep lesions in the basal ganglia, brain stem and thalamus are those most likely to be associated with post-stroke hyperkinesia.
(myoclonus, multiple seizure types and dementia). Other symptoms that have been described include cervical dystonia, corneal endothelial degeneration autism, and surgery-resistant obstructive sleep apnea.
Management
Athetosis, chorea and hemiballismus
Before prescribing medication for these conditions which often resolve spontaneously, recommendations have pointed to improved skin hygiene, good hydration via fluids, good nutrition, and installation of padded bed rails with use of proper mattresses. Pharmacological treatments include the typical neuroleptic agents such as fluphenazine, pimozide, haloperidol and perphenazine which block dopamine receptors; these are the first line of treatment for hemiballismus. Quetiapine, sulpiride and olanzapine, the atypical neuroleptic agents, are less likely to yield drug-induced parkinsonism and tardive dyskinesia. Tetrabenazine works by depleting presynaptic dopamine and blocking postsynaptic dopamine receptors, while reserpine depletes the presynaptic catecholamine and serotonin stores; both of these drugs treat hemiballismus successfully but may cause depression, hypotension and parkinsonism. Sodium valproate and clonazepam have been successful in a limited number of cases.), but can still act against tremors; this indicates that this drug's mechanism of therapy may be influenced by peripheral beta-adrenergic receptors. Primidone's mechanism of tremor prevention has been shown significantly in controlled clinical studies. The benzodiazepine drugs such as diazepam and barbiturates have been shown to reduce presentation of several types of tremor, including the essential variety. Controlled clinical trials of gabapentin yielded mixed results in efficacy against essential tremor while topiramate was shown to be effective in a larger double-blind controlled study, resulting in both lower Fahn-Tolosa-Marin tremor scale ratings and better function and disability as compared to placebo.
Deep brain stimulation toward the ventral intermediate nucleus of the thalamus and potentially the subthalamic nucleus and caudal zona incerta nucleus have been shown to reduce tremor in numerous studies. That toward the ventral intermediate nucleus of the thalamus has been shown to reduce contralateral and some ipsilateral tremor along with tremors of the cerebellar outflow, head, resting state and those related to hand tasks; however, the treatment has been shown to induce difficulty articulating thoughts (dysarthria), and loss of coordination and balance in long-term studies. Motor cortex stimulation is another option shown to be viable in numerous clinical trials.
Dystonia
Treatment of primary dystonia is aimed at reducing symptoms such as involuntary movements, pain, contracture, embarrassment, and to restore normal posture and improve the patient's function. This treatment is therefore not neuroprotective. According to the European Federation of Neurological Sciences and Movement Disorder Society, there is no evidence-based recommendation for treating primary dystonia with antidopaminergic or anticholinergic drugs although recommendations have been based on empirical evidence. Anticholinergic drugs prove to be most effective in treating generalized and segmental dystonia, especially if dose starts out low and increases gradually. Generalized dystonia has also been treated with such muscle relaxants as the benzodiazepines. Another muscle relaxant, baclofen, can help reduce spasticity seen in cerebral palsy such as dystonia in the leg and trunk. Treatment of secondary dystonia by administering levodopa in dopamine-responsive dystonia, copper chelation in Wilson's disease, or stopping the administration of drugs that may induce dystonia have been proven effective in a small number of cases. Physical therapy has been used to improve posture and prevent contractures via braces and casting, although in some cases, immobilization of limbs can induce dystonia, which is by definition known as peripherally induced dystonia. There are not many clinical trials that show significant efficacy for particular drugs, so medical of dystonia must be planned on a case-by-case basis.
History
In the 16th century, Andreas Vesalius and Francesco Piccolomini were the first to distinguish between white matter, the cortex, and the subcortical nuclei in the brain. About a century later, Thomas Willis noticed that the corpus striatum was typically discolored, shrunken, and abnormally softened in the cadavers of people who had died from paralysis. The view that the corpus striatum played such a large role in motor functions was the most prominent one until the 19th century when electrophysiologic stimulation studies began to be performed. For example, Gustav Fritsch and Eduard Hitzig performed them on dog cerebral cortices in 1870, while David Ferrier performed them, along with ablation studies, on cerebral cortices of dogs, rabbits, cats, and primates in 1876. During the same year, John Hughlings Jackson posited that the motor cortex was more relevant to motor function than the corpus striatum after carrying out clinical-pathologic experiments in humans. Soon it would be discovered that the theory about the corpus striatum would not be completely incorrect.
By the late 19th century, a few hyperkinesias such as Huntington's chorea, post-hemiplegic choreoathetosis, Tourette's syndrome, and some forms of both tremor and dystonia were described in a clinical orientation. However, the common pathology was still a mystery. British neurologist William Richard Gowers called these disorders "general and functional diseases of the nervous system" in his 1888 publication entitled A Manual of Diseases of the Nervous System. It was not until the late 1980s and 1990s that sufficient animal models and human clinical trials were utilized to discover the specific involvement of the basal ganglia in the hyperkinesia pathology. In 1998, Wichmann and Delong made the conclusion that hyperkinesia is associated with decreased output from the basal ganglia, and in contrast, hypokinesia is associated with increased output from the basal ganglia. This generalization, however, still leaves a need for more complex models to distinguish the more nuanced pathologies of the numerous diverse hyperkinesias which are still being studied today.