Athetosis and Dystonia

Athetosis is characterized by irregular, slow, writhing, bizarre movements seen in hands and feet. Athetosis is classified as minor athetosis and major athetosis based on its magnitude. Minor athetosis is seen in patients with mild cerebral palsy. Major athetosis is caused by organic lesions of the striatum, including cerebral palsy, as a residual state of encephalitis, and after anoxic encephalopathy. In these conditions, athetosis is commonly seen in combination with dystonia. Dystonia is characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive movements or postures or both. In many cases of dystonia, the affected part of the body shows an abnormal writhing posture in the resting condition, and slow, writhing involuntary movements are superimposed on the abnormal posture with voluntary movement. For childhood-onset patients, dystonia is most commonly generalized; in adults, typically there is focal dystonia. Focal dystonia includes blepharospasm, cervical dystonia, writer’s cramp, and musician’s cramp. It is often task-specific and can be treated with local botulinum toxin injection. Generalized dystonia is caused by long use of neuroleptic drugs (tardive dystonia) and a variety of neurodegenerative diseases.

Chorea and Ballism

Chorea comprises irregular, apparently random movements of varying speeds involving hands, feet, mouth, and tongue. Particularly at the outset of the disorder, the movement may appear purposeful and can be easily imitated. Chorea is seen in association with various medical diseases such as cerebrovascular diseases (hemichorea), autoimmune diseases like Sydenham chorea, thyrotoxicosis, pregnancy, drug intoxication, and hereditary disorders like Huntington disease, neuroacanthocytosis, and dentato-rubro-pallido-luysian atrophy (DRPLA). Treatment with D2-blockers is effective in some cases. Ballism entailsgross violent movements of extremities that look like throwing or kicking. It is commonly caused by a vascular lesion of the subthalamic nucleus or striatum and thus involves contralateral upper and lower limbs (hemiballism). Vigorous muscle contractions irregularly involve the shoulder and pelvic girdles and the proximal limbs. In the chronic stage, each movement becomes less violent and resembles chorea, although it still involves primarily the proximal muscles. Ballism usually responds to medication with diazepam or D2-blockers like haloperidol.

Dyskinesia, Motor Stereotypies, and Tics

Dyskinesia is characterized by complex, irregular involuntary movements involving lips, tongue, extremities, and/or trunk. The term “dyskinesia” is often used to encompass complex involuntary movements that do not fit into another category of involuntary movements. Focal dyskinesia is commonly seen in the lips and tongue (orolingual dyskinesia or oral dyskinesia). Drug side effects are the most common cause of generalized dyskinesia, usually those that influence dopamine such as L-dopa and neuroleptics (drug-induced dyskinesia, tardive dyskinesia). Motor stereotypies are repetitive occurrences of the same movements; movements commonly encountered in this condition range from simple movements like shaking arms and nodding to complex movements. Motor stereotypies are commonly observed in children with Asperger syndrome, Rett syndrome and other automatisms, and mental retardation. In adults, stereotyped movements are seen in cases of severe infectious encephalitis, autoimmune encephalitis (e.g., limbic encephalitis), cerebrovascular diseases involving the frontal lobe, and neurodegenerative diseases like frontotemporal lobar degeneration. Tics are irregular, typically brisk movements ranging from shock-like simple movements resembling myoclonus (simple tic) to complex movements (complex tic). Patients with tics tend to repeat certain movements like blinking or grimacing, but in the patients with Gilles de la Tourette syndrome, tics appear as a variety of movements including vocalization (vocal tic). These patients can stop the movements for several seconds, but it is often followed by rebound; they often feel an urge to move before a bout of tics and feel release after the bout.

Sleep-Related Movement Disorders

Some movement disorders and behavioral disorders appear specifically during sleep or in relation to sleep. These are rapid eye movement (REM) sleep behavior disorders (RBD); restless legs syndrome; periodic limb movement in sleep (PLMS); cataplexy, which manifests itself as sudden falling, head dropping, or jaw dropping due to sudden loss of muscle tone triggered by emotions (laughing in particular); hypnic jerks or hypnagogic myoclonus; fragmentary myoclonus in children; autosomal dominant nocturnal frontal lobe epilepsy; sleep walking and sleep terrors; head banging, and bruxism (grinding of the teeth). Careful history taking or reviewing a home video provides valuable clues, but the gold standard remains video polysomnography (PSG). Some sleep-related movements do not represent “disorders” as such but are harmless, physiological motor phenomena, and are discussed because of their frequency and relevance in differential diagnostic considerations.

Functional (Psychogenic) Movement Disorders

Functional movement disorders are any type of movement disorder due to a brain network disorder where normal function is possible. The terminology of functional movement disorders has changed; in the recent past, these disorders were most frequently called psychogenic. Characteristics of functional movements include incongruity with a known type of involuntary movement; inconsistency in the pattern, degree, and distribution during the clinical course; improvement with distraction; and possible psychogenic background. While the movements are said to be fully involuntary, there is often some suggestibility. In the case of unilaterally predominant tremor, if the patient is requested to repeat voluntary movements with the intact or less affected hand at a certain pace, the tremor frequency might be replaced by the frequency of the voluntary movement, the phenomenon called entrainment.

Myoclonus

Myoclonus is defined as brisk, shock-like, involuntary movements. Hiccup and nocturnal myoclonus are physiological myoclonus. Myoclonus is usually caused by abrupt, instantaneous contraction of muscles (positive myoclonus), but it can be also caused by transient interruption of the ongoing muscle contraction (negative myoclonus, asterixis). Myoclonus is usually irregular, but some myoclonus may occur at certain intervals (rhythmic or periodic myoclonus). Myoclonus is caused by excessive excitation of motor neurons in the motor cortex (cortical myoclonus, epileptic myoclonus), in the brainstem, or in the spinal cord (spinal myoclonus). Cortical myoclonus is commonly associated with convulsive seizures and is also called epileptic myoclonus. Syndromes characterized by myoclonus, generalized convulsion, and cognitive impairment are coined the progressive myoclonus epilepsies and are caused by multiple neurodegenerative diseases.

Tremor

Tremor is broadly classified into physiological tremor and pathological tremor. Depending on the clinical features and the predominant pattern of production, tremor is classified into resting tremor, postural tremor, and kinetic tremor. Tremor is associated with rhythmic contraction of agonist and antagonist muscles, either alternately or simultaneously. Tremor involving muscles in the resting condition is called resting tremor and is seen most commonly in Parkinson disease. Tremor involving muscles during isometric contraction is called postural tremor, and it is most commonly seen in essential tremor. Tremor involving muscles during intended movements (isotonic contraction) is called kinetic tremor, and it is most commonly seen in a lesion of the cerebellar efferent pathway.

Disorders of Increased Muscle Stiffness or Overactivity

Increased muscle stiffness or overactivity (which differs from parkinsonian rigidity or dystonia) can be caused by a variety of disorders of central or peripheral nervous system origin and genetic, autoimmune, or infectious etiology. Increased muscle stiffness may be the cause of some joint movements, particularly when such stiffness is associated with stimulus sensitivity that causes involuntary movements. The conditions discussed in this chapter include stiff person syndrome, progressive encephalomyelitis with rigidity and myoclonus (PERM), acquired neuromyotonia (Isaacs syndrome), hereditary neuromyotonia, tetanus (which has an infectious etiology), Satoyoshi disease, neuromyotonia, and rippling muscle disease. Many of these cases are caused by decreased synaptic inhibition through an autoimmune mechanism.

Definition and Classification of Involuntary Movements

Involuntary movements, also called hyperkinetic movement disorders, are defined as abnormal, unintended movements. They are defined as “abnormal” because not all unintended movements are pathological (reflexive or spontaneous movements also occur but are part of normal function; these include breathing, yawning, blinking, and the like). Involuntary movements can be classified into several categories according to their phenomenological characteristics and then according to the etiology and/or pathophysiology for each kind of involuntary movement. Involuntary movements include tremor, chorea, ballism, athetosis, dystonia, myoclonus, dyskinesia, tics, asterixis, and motor stereotypy. Many of the involuntary movements can occur as side effects of pharmaceutical drugs. Functional or psychogenic involuntary movements are not infrequently encountered.