Tremor, the most prevalent involuntary movement, is characterized by a rhythmic oscillation around a fixed axis, often congruent with the axis of motion of the affected joint or joints (Alty & Kempster, 2011). The frequency (period) and waveform (timing, sequence of muscle activity) of a particular type of tremor is remarkably consistent over time, although the amplitude of the tremor may vary with internal factors (e.g. fatigue, anxiety, stress, emotions) or external factors (e.g. ambient temperature, alcohol or other substance use, environmental conditions or demands) (Bhidayasiri, 2005).

Tremor appears to be the result of alternating contraction of muscles on either side of a joint. The underlying CNS mechanisms of tremor are not clearly understood; there are several interactive factors that may contribute to the motor expression of tremor: the oscillating tendencies of the mechanical systems of joints and muscles; short- and long-loop spinal cord and brainstem reflexes; closed-loop feedback systems of higher motor centers, including the cerebellum.

Identifying when a tremor occurs (activation) is one strategy for classification: tremor may occur only during movement (action tremor), only when at rest (resting tremor), when trying to maintain a relatively fixed posture (postural tremor), or under all of these conditions. Other strategies for identifying tremor involve observing anatomical location, frequency and amplitude. Most tremors increase with higher levels of stress, anxiety or fatigue and decrease or disappear during periods of sleep (Daroff et al., 2012).

Fasciculation is spontaneous discharge from whole or partial motor units, that may be mistaken for tremor (Daroff et al., 2012). On careful observation, fasciculations present as random twitching rather than the rhythmic oscillating contraction seen in tremor. Fasciculation can occur in motor neuron diseases like amyotrophic lateral sclerosis or primary lateral sclerosis. Fasciculation may also be seen as a result of anticholinergic drugs and stimulants (e.g. excessive caffeine), electrolyte imbalance or sodium deficiency, muscle denervation, nerve root irritation (herniated intervertebral disc or spondylosis). Fasciculation can sometimes be observed in periods of extreme stress or fatigue, or following excessive strenuous exercise.

Myoclonus (clonus) is sudden, brief involuntary movement caused by muscular contractions (positive myoclonus) or inhibitions (negative myoclonus). Due to its rhythmic involuntary nature, it can resemble tremor (Weiner & Lang, 2005). Myoclonus occurs under three circumstances:

Myoclonus associated with hyperactive stretch reflexes can be transient (lasting for several beats) or sustained over a period of time (mimicking tremor). It can be ‘triggered’ by rapid elongation of affected muscles, as in deep-tendon reflex testing; rapid passive range of motion (commonly examined at the ankle with a quick stretch of the gastroc-soleus by dorsiflexion); or during position change. The peripheral mechanism of myoclonus is the same as that of the stretch reflex: annulospiral ‘endings’ around intrafusal fibers within the muscle spindle are stimulated by elongation of muscle tissue. Information about change in length is carried to the CNS via 1a afferent neurons in peripheral nerves. These 1a neurons synapse directly with alpha-motor neurons in the anterior horn of the spinal cord or motor cranial nerve nuclei. If stimulated sufficiently, alpha-motor neurons trigger the activation of the motor units of the elongated extrafusal muscle. The resulting contraction elongates the antagonistic muscles on the other side of the joint, triggering the stretch reflex. Deep tendon reflexes are classified as follows: 0 (absent), 1+(hypoactive), 2+(normal), 3+(hyperactive response without clonus) and 4+(hyperactive response with myoclonus) (Paz & West, 2008). Many individuals with myoclonus associated with pyramidal system dysfunction also exhibit a positive Babinski response when the lateral plantar surface of the foot is stimulated (an upward-pointing hallux with fanning of the second to the third toes).

Myoclonus observed during seizures may involve a single limb segment (in a partial seizure of the opposite motor cortex) or rhythmic jerking of multiple limbs (in a generalized tonic–clonic seizure of the entire cortex). The combination of altered consciousness and myoclonus differentiates the involuntary movement of seizures from tremor. An electroencephalogram (EEG) recorded during either partial or generalized seizure demonstrates abnormal electrical activity of the motor cortex, whereas EEG patterns in those with tremor are less likely to be grossly abnormal (Raethjen et al., 2007; Muthuraman et al., 2008; Shibasaki, 2012).

Hiccups and ‘sleep starts’ (nocturnal myoclonus) are examples of physiologically triggered myoclonus. Movement-triggered myoclonus has been reported during recovery from severe cerebral hypoxia or ischemia following myocardial infarction or near drowning. Myoclonus may occur as a component of uremic or hepatic encephalopathy and with degenerative disorders, as in Alzheimer’s disease. Occasionally, myoclonus may be caused by drug toxicity (e.g. penicillin, tricyclic antidepressant, levodopa) (Rowland & Pedley, 2010).

Tics are brief and intermittent movements (motor tics) or sounds (phonic tics) that can resemble myoclonus and tremor as well as the dance-like involuntary movement of chorea (Daroff et al., 2012). Tics can be classified as ‘simple’, involving brief irregular muscle twitching of an isolated body segment, as in the case of repetitive eye blinking, throat clearing, or shoulder shrugging. Tics can also present as ‘complex’, for example in the case of coordinated, patterned movements involving several muscles, as in arm gesturing, skipping while walking, and whistling or stuttering (Rowland & Pedley, 2010; Daroff et al., 2012). Those experiencing tics will describe a sense of increasing muscle tension that can only be relieved when the stereotypical movement occurs. Tics differ from other types of involuntary movement in that they are somewhat under voluntary control and can be suppressed for a length of time. Idiopathic tics often occur for short periods of time, sometimes in childhood, and may be associated with anxiety or other psychological stress factors. Tics differ from other dyskinetic movement disorders as they may be evident during all stages of sleep, although they may subside with sleep. Tics associated with Tourette’s syndrome may persist over the lifespan and include vocalizations (barking, grunting, echolalia and repetitive swearing) as well as stereotypical facial or extremity movement.

Dystonia is a movement disorder characterized by a sustained positioning or a very slowly changing abnormal synergistic movement (Alarcon et al., 2004). It can affect one or more body segments, often observed as tonic abnormal posturing in individuals with longstanding damage to the pyramidal motor system (e.g. severe equinovarus after significant stroke or other acquired brain injury, or spastic cerebral palsy). Dystonic positions are described as abnormal; they cannot be accurately mimicked or recreated volitionally. Individuals with dystonia associated with pyramidal system dysfunction may also exhibit myoclonus and hypertonicity.

Some dystonias are idiopathic and may be familial (e.g. spastic torticollis). Others occur only during one specific motor activity (e.g. writer’s cramp or laryngeal dystonia during public speaking). Facial hemispasm is an intermittent focal dystonia related to compression or irritation of the seventh cranial nerve. If idiopathic torsion dystonia develops in later life, it most commonly affects axial, facial or upper extremity muscles and may challenge feeding, communication and other activities of daily living (ADLs). Most idiopathic dystonias are nonprogressive.

Secondary dystonias may be associated with damage to the putamen nucleus of the basal ganglia resulting from a tumor, ischemia or infarct, or head injury. Dystonia may be one of the signs of progressive degenerative diseases such as supranuclear palsy, Huntington’s disease, Wilson’s disease or Parkinson’s disease. Dystonic postures may emerge in the end-stages of Alzheimer’s disease.

Medications used to manage dystonia and spasticity must be closely monitored owing to adverse side-effects. Medications include: benzatropine mesylate (Cogentin), diazepam (Valium), dantrolene (Dantrium), haloperidol (Haldol), baclofen (Lioresal, Clofen), tizanidine hydrochloride (Zanaflex), carbamazepine (Tegretol) and Gabapentin (Neurontin) (Ciccone, 2007; Gladson, 2010). Severe focal dystonia may be temporarily treated with injection of botulinum toxin.

Chorea is a less common dyskinesia consisting of the random and rapid involuntary contractions of muscle groups, mostly of the extremities or face (Rowland & Pedley, 2010). Proximal and/or distal muscle groups of the extremities may be affected. Typically, muscles of the axial skeleton are not involved; therefore, postural control is not significantly compromised.

Chorea occurs when there is damage to the corpus striatum (basal ganglia), especially the caudate nucleus and putamen; however, the exact localization and pathophysiology of chorea is uncertain (Patestas & Gartner, 2006). Some choreas are hereditary (e.g. Huntington’s disease), whereas others are a consequence of another physiological disease or trauma (Blumenfled, 2010). Choreic movement also occurs with tardive dyskinesia, a complication of the long-term use of certain neuroleptic drugs (e.g. in the management of schizophrenia) or dopamine toxicity (e.g. in the management of Parkinson’s disease) (Caligiuri et al., 2000).

The quality of choreiform movement is often described as graceful or dance-like. Individuals learn to blend their involuntary movement with a purposeful movement in an attempt to mask or minimize the unwanted movement (e.g. a choreic movement of the arm over the head might be turned into smoothing of the hair). People with chorea will often have difficulty sustaining contractions (e.g. ‘milk-maid’s handshake’ – the patient contracts and relaxes when asked to maintain a constant, firm grip during a handshake). As with tremor, choreiform movements become more obvious in periods of stress and may disappear during sleep. Pseudochorea has been reported in individuals with impairment of proprioception resulting from multiple sclerosis and other diseases of the dorsal columns.

Athetosis occurs when there has been damage to the corpus striatum (caudate and putamen) in the basal ganglia, most often in children with perinatal ischemia and hypoxia or severe bilirubin toxicity. In the past, athetosis was referred to as the basal ganglia form of cerebral palsy. Currently, the term dyskinetic cerebral palsy is preferred and the use of athetosis is recommended only to indicate a particular type of movement independent of etiology. Although the severity of athetosis does not change with maturity, function may become more challenging in aging individuals with athetosis because of typical age-related changes and increased incidence of musculoskeletal and neuromuscular pathologies that are common later in life. Pseudoathetosis may occur in adulthood due to severe distal sensory loss (Spitz et al., 2006).

Ballismus is a rarely occurring movement disorder that presents as wild and forceful flinging movements of one or more of the extremities that are rapid and nonpatterned (Arminoff, 2008; Klein, 2005). Trunk and facial muscles are usually spared and bulbar functions (e.g. speaking, swallowing, breathing) are not impaired. Ballismus is usually unilateral (hemiballismus) and movements are much more stereotypical and disruptive than those seen in chorea. It may be suggested that ballism and chorea represent a continuum rather than distinct entities (Daroff et al., 2012). Ballismus differs from other dyskinesias in that these involuntary motions do not tend to decrease in frequency or amplitude during periods of sleep.

Ballismus is thought to occur when there has been damage or disruption to the subthalamic nuclei in the diencephalon. Alteration of neural output from the subthalamus apparently ‘releases’ the activity of the globus pallidus nuclei, which unleashes stereotypical synergistic movement of the limb girdle and extremity. It occurs most often as the result of a ‘lacunar’ stroke of the lenticulostriate branches of the middle cerebral artery, which damages the subthalamus deep in one cerebral hemisphere. Haloperidol (Haldol) is often used to control unwanted and disruptive motion during the acute and early rehabilitation phases of care, and to promote more effective sleeping. Fortunately, hemiballistic movement tends to diminish in both amplitude and frequency in the weeks following a stroke; however, more subtle choreoathetotic movements may persist (Blumenfled, 2010).

Asterixis, also referred to as negative myoclonus, occurs as a brief and recurrent loss of sustained muscle contractions in postural muscles of the extremities and trunk (Rubboli & Tassinari, 2006; Rowland & Pedley, 2010). Asterixis is observed during neurological examination when the person being assessed exhibits ‘flapping’ of the hands when asked to hold their arms horizontally with wrists extended against gravity. Asterixis may occur in individuals with toxic metabolic encephalopathy as a result of hepatic, renal or pulmonary disorders. It has also been reported as a consequence of drug toxicity, during anticonvulsant therapies and when there is a lesion interrupting interconnections between the brainstem and thalamus.

Akathisia, often called restless leg syndrome, is a distressing subjective sense of tension and discomfort of the limbs that is often associated with agitation and a need to move around, but that is not always relieved by movement (Weiner & Lang, 2005). Restless leg syndrome occurs in 10–35% of people over the age of 65 (Milligan & Chesson, 2002). Those with the clinical diagnosis of akathisia report difficulty sitting or lying still and a powerful urge to move. They may pace or rock in place and often complain of difficulty sleeping. Akathisia can be idiopathic or can be an extrapyramidal side-effect of antipsychotic medication. It may be the presenting symptom in someone who is developing tardive dyskinesia (see Drug-induced Movement Disorders below). The FDA has approved three drugs for the management of restless leg syndrome, including pramipexol (Mirapex), ropinirole (Requip) and gabapentin enacrabil (Neurontin Horizan) (Milligan & Chesson, 2002).

Huntington’s chorea is an autosomal dominant hereditary progressive disorder involving degeneration of the corpus striatum (Rowland & Pedley, 2010; Daroff et al., 2012). The gene for Huntington’s is located on the short arm of chromosome 4. The three characteristic signs of Huntington’s chorea are movement disorder (chorea), dementia and personality disorder. The first signs and symptoms of the disease appear in midlife (35–40 years) as restlessness, emotional lability, neurosis or personality disorders. Over time, cognitive impairment becomes more apparent and choreiform involuntary movement develops, often impairing judgment, locomotion and mobility, speech production and swallowing. As the severity of symptoms increases, functional status deteriorates. Dystonia and rigidity may develop late in the disease process.

On CT or MRI there is marked bilateral degeneration of the caudate nucleus, enlargement of the anterior horn of the lateral ventricles and cerebral atrophy. Treatment of Huntington’s disease is symptomatic; choreiform movement can sometimes be managed with dopamine-blocking agents such as haloperidol, reserpine or tetrabenazine. Individuals with Huntington’s disease may have to cope with their increasingly debilitating impairments for 10–25 years, until the disease takes their life.

Wilson’s disease (WD) is a rare autosomal recessive hereditary disorder of copper metabolism, with a mutation on chromosome 13 (Rowland & Pedley, 2010; Daroff et al., 2012). Many patients present in childhood with signs of liver disease and failure associated with the accumulation of copper. Although initial symptoms typically appear in adolescence and early adulthood, presentation may first occur as late as 60 years of age. If undetected early in life, Wilson’s disease can be fatal.

Nearly half of patients with WD present with CNS signs and symptoms (Daroff et al., 2012). Neurological symptoms of poorly managed WD include resting or postural tremor, chorea of the extremities, dystonia, pseudobulbar palsy and cognitive dysfunction. The abnormal liver function associated with WD eventually leads to chronic cirrhosis. Traditionally, the acute management of the disease began with penicillamine, but more recent treatment strategies include the use of trientine and zinc (removes excess copper) or ammonium tetrathiomolybdate (to block copper absorption), which are less toxic but still being researched. Orthotopic liver transplantation has been found to correct the underlying pathology in those individuals in severe hepatic failure without the presence of neurological symptoms (Daroff et al., 2012).

Paroxysmal kinesigenic dyskinesia (PKD or paroxysmal kinesigenic epilepsy), formerly known as paroxysmal choreoathetosis, presents as jerking and writhing movements of the limb and trunk when an individual is unexpectedly startled or disturbed (Daroff et al., 2012). The movements may be unilateral or bilateral lasting about 1 minute and can occur up to 100 times daily. Paroxysmal dyskinesia initiates in childhood, however this condition persists later in life. PKD is responsive to anticonvulsant medication such as carbamazepine and phenytoin.

Paroxysmal nonkinesigenic dyskinesia (PNKD), formerly known as familial choreoathetosis, is a rare autosomal dominant hereditary movement disorder that is relatively benign, with onset in childhood or early teens (Rowland & Pedley, 2010). In this condition, the individual experiences intermittent ‘attacks’ or spells of dystonia, chorea, athetosis, ballismus or a combination of movements that are associated with periods of physical exertion or ingestion of alcohol or caffeine. The ‘attack’ frequency can range from several episodes per month to several episodes per day, and last between 10 minutes to several hours (Daroff et al., 2012). This condition may lessen with age.

Senile (or essential) chorea is a late-appearing idiopathic movement disorder that evolves in the absence of psychotropic or dopamine therapy, Huntington’s chorea, dementia or familial movement disorders (Daroff et al., 2012). Also known as oral–facial–lingual dyskinesia, senile chorea primarily affects the muscles of the mouth, tongue and jaw. It is important to differentiate the abnormal involuntary movements of senile chorea from the similar facial movements that occur in tardive dyskinesia and the lip and jaw movements commonly observed in older individuals who have lost all of their teeth and are no longer able to wear dentures. Antidopaminergic drugs are the most effective when monitored carefully to assess for the development of tardive dyskinesia.

Tourette’s syndrome is a genetically determined chronic neuropsychiatric disorder that is characterized by multiple motor and vocal tics (Hallett, 2003; Daroff et al., 2012). Symptoms may occur initially in childhood or adolescence and persist into adulthood and later life. Initially, many individuals with Tourette’s are misdiagnosed with a psychiatric illness.

Initial motor tics typically involve the face and eyes, and may eventually include vocalizations (repetitive grunts, barks, throat clearing, cursing, echolalia). Repetitive motor tics of the extremities can resemble chorea. Although Tourette’s is documented as an autosomal dominant trait, other hypotheses are: it is considered to be a disorder of the basal ganglia that involves excessive levels of the transmitter dopamine; a limbic system disorder involving dysfunction of the central endogenous opioid system; and reports of Tourette’s following head trauma, toxic and metabolic encephalopathies, and Huntington’s disease are more likely to be coincidental than causal.

Tourette’s can cause considerable social, vocational and functional impairment and may also be associated with obsessive–compulsive behavior, attentional and executive dysfunction, sleep disorders and aggressive behavior (Hankey & Wiardlaw, 2008). Lifelong pharmacological intervention including dopamine-blocking agents, clonidine, haloperidol or pimozide can assist with community reintegration without compromising life expectancy.

Extrapyramidal dysfunction also occurs as the undesirable side-effect of antipsychotic drugs and other medications (Caligiuri et al., 2000; Lee et al., 2005; Morgan & Sethi, 2005). Because drug metabolism and excretion mechanisms become less efficient with aging, older adults are more susceptible to drug toxicity and adverse drug reactions; the medications that older adults are prescribed may remain physiologically active for longer periods of time, especially if dosage is not adjusted for age and body composition (Ciccone, 2007; Gladson, 2010). Classes of medications associated with extrapyramidal side-effects are outlined in Table 31.2.