CHAPTER 130

Tics

Hanalise V. Huff, MD, MPH, and Kenneth R. Huff, MD

A tic is a brief, abrupt, nonpurposeful movement or utterance. Tics occur in a background of normal activity and are repetitive and involuntary but can be suppressed. Tourette syndrome (TS) is the most common etiology of tics in children. It is defined by multiple types of tic displayed over time, including motor tics and vocal tics. Tourette syndrome most frequently manifests solely as a nondis-abling movement disorder but may also be associated with other neurobehavioral problems, which may include attention-deficit/ hyperactivity disorder (ADHD), obsessive-compulsive disorder, mood and rage disorders, anxiety, personality and conduct difficulties, and sleep disorders.

Epidemiology

Tics are relatively common in children but often go unrecognized as a movement disorder. The onset of tics associated with TS is generally between 5 and 12 years of age but can be as late as 21 years of age. The prevalence of tics is 5 times higher in males than females. By various estimates, TS prevalence is between 0.1% and 3%, and many cases of TS are familial, with some features occurring in a parent in up to 25% of cases. Family members may have had such mild symptoms that they never sought medical attention. The risk of TS in a sibling is approximately 8%. Tics are more common in male family members, but other family members may have only non-tic manifestations of the syndrome, such as obsessive-compulsive symptoms, which occur most often in females. Tourette syndrome appears to be less common among sub-Saharan Africans and African-Americans.

Clinical Presentation

Children with tics display sudden repetitive movements of the face, neck, shoulders, or hands in the context of normal behaviors, and normal behaviors are sometimes used to mask the tics. Sometimes tics can be suppressed when they would be embarrassing or during a time of intense physical activity, concentration, or performance, but they also may be worsened by stress or strong emotions. Tics associated with TS vary in their manifestations over periods of weeks to months. Some examples of tics are blinking, eye rolling, grimacing, neck stretching, head turning or shaking, shoulder shrugging, stomach tensing, and wrist flicking. Many affected children describe a brief premonitory sensation, which is an indescribable, uncomfortable feeling that is subsequently relieved by the motor tic. Tics may bizarrely mimic normal, sometimes complex, movements or postures or involve a series of orchestrated simple movements, such as sequential finger flexing, wrist bending, and arm stretching. Tics may include sudden repetitive sounds from the vocal apparatus (Box 130.1), which may be produced by a sudden movement of air or saliva within the larynx or pharynx or a clicking of the tongue or teeth. Sounds may include throat clearing, sniffing, grunting, squeaking, sucking, or blowing. Additionally, children with TS may also have socially inappropriate words or gestures or repeat a new word or phrase or a word or phrase they have just said or heard.

Children with TS may have learning problems, including easy distractibility and inability to finish schoolwork. Less frequently, they also have intrusive or repetitive thoughts, unfounded fears, or ritualistic actions that may involve touching, cleanliness or neatness, counting and exactness, symmetry or evenness, or irrational checking. Sleep disturbances are not unusual.

Classifications of tics according to the nature of the action can be helpful in understanding apparently widely different movements as being part of the same disorder because of ultimately shared central nervous system chemistry or circuitry (Box 130.2). Clonic tics are brief, and dystonic tics are more sustained movements. In addition to simple tics, patients may rarely have other unusual behaviors (ie, complex tics) including echopraxia (ie, repetitive gestures), copropraxia (ie, obscene gestures), and coprographia (ie, obscene writing). Unusual speech patterns include irrelevant or nonsense words, palinphrasia (ie, repeating one’s own words), echolalia (ie, repeating another’s words), and coprolalia (ie, obscene speech). Diagnosis is often delayed because of misunderstandings about the common and uncommon manifestations of TS (Box 130.3).

Pathophysiology

Tics are thought to be generated from a functional abnormality of circuitry in deep brain nuclei that might include the striate nuclei, globus pallidus, subthalamic nuclei, and substantia nigra. The prefrontal cortex, thalamus, and limbic systems may also be involved. Tourette syndrome, including the generation of the tic movement disorder, must result from several brain-expressed genes with a developmentally influenced expression interacting in a complex manner with psychosocial and other environmental factors and thus making it a true neuropsychiatric condition.

Dopaminergic disinhibition within the circuitry is likely to be part of the abnormal function because of 1 class of medication (eg, stimulants) worsening the symptoms and another class (eg, dopamine antagonists) effective as a treatment. In patients with TS, the cerebrospinal fluid contains low baseline levels of homovanillic acid, a dopamine metabolite, which could result, as has been hypothesized, from a hypersensitive dopamine receptor. Additionally, amphetamines and methylphenidate hydrochloride increase dopamine release, and in some instances, these agents precipitate tic symptoms. Haloperidol, an effective tic-suppressing medication, blocks dopamine receptors and, therefore, may block a potentially hypersensitive Tourette dopamine receptor. The observation of a good clinical response with relatively low doses of dopamine blockers (eg, haloperidol) and the finding of increased homovanillic acid levels resulting from receptor desensitization long after dis-appearance of the drug support this hypothesis. The physiology is undoubtedly more complex, because medications involving other transmitters also are effective. Rare genetic causes of TS are mutations in the SLITRK1 gene, which is involved in dendrite growth, and the gene for histidine decarboxylase, HDC. Histamine decarboxylase converts histidine to histamine in histaminergic neurons found in the posterior hypothalamus but connecting widely in basal ganglia and other brain regions. It is unknown how either of these genes causes symptoms, and the genetic basis of TS remains elusive.

An observed association of the sudden onset or exacerbation of obsessive-compulsive or tic symptoms with preceding group A streptococcal infections of the pharynx has been termed pediatric autoimmune neuropsychiatric disease associated with streptococcus (PANDAS). Although for some time it has been known that a clear relationship exists between the same bacteria and another movement problem, Sydenham chorea, the evidence for causality or any role of the bacteria or of related autoimmunity is conflicting and unconfirmed by large studies involving TS or obsessive-compulsive disorder; therefore, routine screening or prophylaxis has not been recommended when these diagnoses or PANDAS are being considered.

Differential Diagnosis

The duration, frequency, and appearance of the movement, the premonitory sensation, and circumstances of occurrence of tics help distinguish them from several other episodic movement disorders. Myoclonus is a lightning-like, nonsuppressible jerk of a small group of muscles, and chorea involves nearly constant, small amplitude movements of the fingers, hands, and feet that are often accompanied by grimacing movements of the face. Tremor is an oscillatory movement of an extremity or the head. Hemiballismus is an uncontrollable episodic throwing movement of an extremity. Hyperekplexia is a hyperactive startle response provoked by touch or sudden noise. Torticollis, or neck writhing, may be paroxysmal but is generally part of a benign transient disorder or a chronic degenerative disorder, such as familial dystonia. Paroxysmal kinesigenic choreoathetosis, an unusual episodic condition precipitated by a sudden movement, is characterized by a twisted trunk and limb posture lasting a few seconds (longer than tics, generally) and not accompanied by loss of consciousness. Hypnagogic jerks and bruxism are persistent normal variant behaviors that occur in sleep.

Other repetitive behaviors are sometimes confused with tics. A compulsion is a complex action that is done against an individual’s will or better judgment. A stereotypy is a persistent repetitive senseless movement. A perseverative behavior involves continued activity after the cause of it has ceased. The most common self-injurious behaviors are biting or banging of a body part during periods of agitation. An addictive behavior occurs with psychological dependence caused by a reward system. A habit is a fixed practice established by repetition. A mannerism is a stereotyped movement or habit peculiar to an individual and part of that individual’s personality. An anger outburst is a sudden emotion-generated behavior occurring with relatively little provocation.

Tic disorders are sometimes divided into 3 groups: simple transient tics, which are monomorphic (ie, always the same appearance over a period of months), last less than 12 months, and may be caused by particular environmental situations or psychological states; chronic tics, which last longer than 12 months but are of a single type; and the tics of TS (Box 130.4). All 3 types of tic disorders may occur in the same family. Tics can also be seen in association with Huntington disease, neuroacanthocytosis, Sydenham chorea, infectious encephalitis, carbon monoxide poisoning, stroke, schizophrenia, head trauma, static developmental encephalopathies, and drug reactions, particularly stimulants, anticonvulsant agents, and antipsychotic agents.

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