Abnormal involuntary movements are also known as "Dyskinesia". There are several different varieties of dyskinesia which have different clinical appearances, underlying etiologies, and treatments. Tremor, Chorea, Dystonia, and Myoclonus are examples of types of dyskinesia which have different mechanisms and modalities of treatment. Strictly speaking Epileptic Seizures represent the "ultimate" abnormal involuntary movement. Tics and Stereotypies may also be considered to be related, but some experts call these "unvoluntary" because there is an element of voluntary control.

People with severe brain dysfunction may experience several co-exisiting types of dyskinesia which makes evaluation and management more difficult. Staff who care for people with developmental disabilities are rarely trained to correctly identify and diagnose the various abnormal involuntary movements which they may observe. Professionals who are called upon to treat may be given inaccurate information. For example stereotypies may be confused with seizures or myoclonus, which leads to ineffective or even harmful interventions.

Several types of dyskinesia will be discussed below: Dystonia, Myoclonus, and Tremor

Dystonia is one type of involuntary movement, characterized by intermittant episodes of sustained contraction of one or more muscle groups which causes a twisting/distortion of that part of the body resulting in an abnormal posturing or positioning.

Dystonia is a symptom of damage to or dysfunction of the basal ganglia. There are many different causes of damage to or dysfunction of the basal ganglia resulting in the symptom of dystonia; hence there are many different clinical conditions which are classified as "The Dystonias". Dystonia can be classified "Anatomically"(what part of the body is affected) or "Etiologically"(what caused the dystonia).

Anatomically, dystonia can be "generalized" or "focal". The disease known as "Idiopathic Torsion Dystonia" is a type of generalized dystonia that ususally starts in childhood in one foot or leg, but later spreads to other body parts. Examples of focal dystonia include "Blepharospasm" (spasms of the eyelids), "Torticollis"(spasms of the neck muscles), "Meige's Syndrome (spasms of the muscles of the jaw resulting in opening or closing of the mouth), "Spasmodic Dysphonia" (spasms of the laryngeal muscles resulting in speech abnormalities), and "Writer's Cramp" (spasms of the hand muscles during hand use).

Etiologically, dystonia can be either "Inherited" or "Acquired". Inherited causes of dystonia include some cases of Idiopathic Torsion Dystonia , Dopa-Responsive Dystonia, X-Linked Dystonia-Parkinsonism, and a type of inherired dystonia found in Ashkenazi Jews. Acquired causes of dystonia include anything that can cause damage/dysfunction of the basal ganglia. Examples include hypoxic-ischemic brain damage during the peri-natal period, infections, multiple sclerosis, metabolic conditions such as Wilson's disease, Kernicterus, and drug toxicity from neuroleptic medication(tardive dystonia).

Episodes of dystonia may be triggered by physical stimulation (eg any bodily movement), emotional excitement, or environmental stimuli such as excessive noise. It appears that the sensory "gate-keeper" function normally provided under conditions of sensory stimulation by the basal ganglia, does not occur properly in people with dystonia.

Treatment of dystonia can be accomplished with oral medication, Botulinum Toxin Injections, and surgery. Intrathecal Baclofen may be effective in some types of dystonia.

Oral drug therapy might include Artane, Cogentin, Valium, Klonopin, Lioresal, Tegretol, Sinemet, Parlodel, or Symmetrel.

Surgical procedures to be considered include thalamotomy, pallidotomy, rhizotomy, selective peripheral denervation, or muscle resection.

Dystonia is not rare in people with developmental-onset chronic brain disorders (i.e. Developmental Disabilities), and sometimes interferes with work and school function as well as with the activities of daily living. It is therefore important to identify and diagnose dystonia because many potentially beneficial treatments exist.

MYOCLONUS

Myoclonus is defined as a sudden, severe involuntary contraction of any muscle group. Myoclonus can be isolated or generalized. Myoclonus is caused by damage or dysfunction of the brain or spinal cord. Virtually any disease that can damage the brain and/or spinal cord can cause the symptom of myoclonus. Thus there may be metabolic, traumatic, vascular, infectious, degenerative, toxic, or hereditary etiologies. Therefore myoclonus may be associated with other symptoms of CNS dysfunction such as mental retardation, cerebral palsy, impulse control disorders, or epilepsy.

Myoclonus can be confused with epilepsy. Epilepsy is caused by electrical instability of the cortex of the brain, while myoclonus is caused by abnormal electrical discharges in the brain stem or spinal cord. Therefore, while muscle jerking may occur in both epilepsy and myoclonus, alteration of consciousness will only be seen with epilepsy because of spread of abnormal discharges in the cerebral cortex found in epilepsy.

The distinction between myoclonus and epilepsy can be especially confusing if the patient is experiencing "simple partial seizures" that do not spread and cause alteration of consciousness. Also patients with myoclonus as a result of damage/dysfunction localized to the brain stem can at times develop epileptic seizures if the abnormal brain stem electrical activity spreads to the cortex as well as to the corticospinal tracts. These conditions can be analyzed by simultaneous recording of cortical activity (EEG) and muscle activity (EMG). If cortical discharge precedes muscle discharge it's epilepsy. On the other hand if muscle discharge precedes cortical activity the diagnosis would be primary myoclonus, with secondary spread to the cortex and epilepsy.

The pathophysiology of myoclonus is not well understood, but appears to be related to a failure of the brain stem and/or spinal cord to control motor response to a variety of stimuli. Proprioceptive stimulation from any movement often triggers myoclonic jerks in people with severe developmental-onset chronic brain disorders. Sudden loud noises can also trigger myoclonus. It is possible, in people with developmental disabilities, that any form of excessive stimulation can lead to myoclonic muscle jerking. Examples might include abnormal stimuli from the gastrointestinal tract (GERD, constipation), pulmonary infection, environmental conditions, and emotional excitement.

It is important to diagnose and treat myoclonus, because it can interfere with the activities of daily living and can lead to injury from falls. Treatment should include optimizing the environment to reduce noise and conditions that lead to emotional excitement, elimination of underlying medical conditions such as infection, constipation, and drug toxicities, and the use of medications shown to be effective in treating myoclonus. Medications used to treat myoclonus include Mysoline, Klonopin, and Depakote, either alone or in combination.

TREMOR

Rhythmic oscillatory (to-and-fro) movements of muscle groups is normal. This movement is normally so rapid (greater than 12 Hz) that it is not perceived. This is analogous to the flicker of a fluorescent light bulb which occurs so rapidly that to the human eye the appearance is that of constant light. If the "starter/pacemaker" of the fluorescent light wears out or becomes defective, the flicker frequency will slow down so that it then becomes perceptable to the human eye.

When rhythmic oscillations of body parts become perceptable, those oscillations are called "tremor". Tremor is probably caused by dysfunction of the basal ganglia and/or cerebellum. The basal ganglia contain neuronal "pacemaker" activity which regulates conduction of impulses routed through the thalamus. When this pacemaker activity fails, tremor results because of loss of "gatekeeper" control of these impulses.

Tremor can be normal or physiologic (8-12 Hz); for example, during times of fear, stress, or following excessive physical activity.

It is useful to divide tremor into three categories; 1) Tremor at rest ,2) Tremor with movement (intention tremor), or 3) Essential tremor.

Resting tremor is usually slow (4-6Hz) is present during inactivity, but disappears with action. This type of tremor is typical of Parkinson's disease and can be treated with various preparations of L-Dopa.

Intention tremor occurs during activity and increases in severity as the limb approaches its target. It can be seen as a result of cerebellar dysfunction or as the result of toxicity from alcohol or certain anti-convulsants(eg Depakote). Stereotaxic lesions to the ventrolateral nucleus of the thalamus can relieve this tremor when it is secondary to cerebellar disease.

Essential tremor may be inherited and may occur at rest or with activity. While felt to be benign, it may be disabling by interfering with handwriting, spilling of liquids, and other activities of daily living. Inderal , Mysoline, Corgard, Klonopin, Xanax, and Valium are some of the drugs which may provide relief from essential tremor. The Medtronic company is now marketing a "Thalamic Stimulator", which is neurosurgically implanted into the thalamus, thus serving as a "pacemaker" to the thalamus to reduce essential tremor.

Although good statistics are not available, tremor in patients with developmental-onset disabilities is probably usually secondary to drug toxicity, but may be associated with dysfunction of the basal ganglia and/or cerebellum, or may be essential.

Accurate diagnosis is important because of the availability of effective treatments.