Tics are brief, sudden, repetitive movements (motor tics) or utterances (phonic or vocal tics) that are temporarily suppressible and are usually preceded by a strong urge to perform the tic. The distinction between motor and vocal tics is somewhat arbitrary because production of vocal tics requires the involvement of facial, oropharyngeal, or diaphragmatic musculature. The Gilles de la Tourette syndrome, named after the author of the seminal description and commonly shortened to Tourette syndrome (TS), is the most well-described tic disorder.

TS is a neurobehavioral disorder consisting of both multiple motor and phonic tics (not necessarily concurrently) that change in character over time, beginning before 18 years of age, and with symptoms that wax and wane but last more than 1 year. For the diagnosis of TS, these motor and phonic tics are not caused by exogenous factors such as cocaine or a medical condition such as encephalitis or trauma. Although the earlier definition as proposed by the American Psychiatric Association in its Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), is a useful criterion for research on the disorder, it excludes chronic tics in the motor or vocal domains alone, which are likely milder expressions of the same condition (Table 74.1). Other causes of ticlike syndromes include neuroacanthocytosis, encephalitis, prior neuroleptic use, and head trauma. Many patients with TS have a behavioral component of obsessive-compulsive disorder (OCD), attention deficit disorder (ADD), anxiety, or poor impulse control. These behavioral features usually impose more disability than do the tics.

Primary tics not part of TS may be classified under chronic motor/vocal tic disorder, in which tics persist beyond 1 year, or transient motor/vocal tic disorder, in which tics last less than 1 year, the latter being the most common tic disorder in children. Most adults with tics had idiopathic tics as children, but primary or secondary tic disorders can develop in adulthood. Insult to the basal ganglia by diverse mechanisms including stroke, infection, trauma, autoimmune process, or neurodegenerative disease can cause the appearance of tics, possibly via disruption of dopamine circuits. Similar to tardive dyskinesias, tardive tics may appear after varying lengths of treatment with antipsychotics or as a consequence of discontinuation of treatment. Substances such as caffeine, stimulants, and certain antiepileptics (carbamazepine, lamotrigine) have been reported to exacerbate or provoke the emergence of tics. Tics generally follow an anatomic distribution more heavily weighted toward the craniocervical regions than the trunk and limbs. Tics are rarely of psychogenic origin but due to similar clinical features are often difficult to differentiate from organic tics.

Estimates of prevalence rates of tics have varied broadly, depending on clinical definitions, the age range of participants, and other features of study design. Studies of children yield higher prevalence estimates than do studies of adolescents and adults, as tics typically attenuate in severity or remit entirely by young adulthood. Conservative estimates for lifetime prevalence rates are 1 per 1,000 in boys and 2 per 10,000 in girls. On average, tics begin around age 5 years and increase in severity, reaching a most intense period around age 10 years. After that, tics usually decline in severity until, by age 18 years, nearly half of the patients are virtually free of tics.

Research into the pathobiology of tics has focused mainly on Tourette but the causes of TS are still unknown. The search for genetic mutations has yielded modest evidence for linkage to chromosome 11q23 in a large French Canadian family and to 11q23-q24, 2p11, and 8q22 in Afrikaner families, although these findings generally have yet to be replicated. A de novo chromosomal inversion on chromosome 13q31.1 in a child with TS led to identification of a frameshift mutation in SLITRK1, a gene that promotes dendritic growth, as one rare cause of TS. Although early family studies suggested that the genetic transmission of TS is autosomal dominant with a strong sex-specific difference in penetrance, more recent studies have indicated that the mode of inheritance is more complicated than this, appearing semidominant and semirecessive and having greater penetrance in homozygotes than in heterozygotes.

Anatomic MRI has documented reduced volumes of the basal ganglia, particularly the caudate nucleus, as well as thinning of sensorimotor, primary motor, and premotor cortices in persons with TS. These findings are thought to represent hypoplasia in motor portions of the cortical-basal ganglia circuits, and these developmental disturbances contribute to the genesis of tic behaviors. Preliminary postmortem studies suggest the presence of reduced GABAergic interneurons in the basal ganglia, possibly contributing to excess excitability of these motor circuits. Separate circuits within the prefrontal and parietal cortices, and in the hippocampus, are thought to help modulate tic-generating activity in the basal ganglia and motor cortices, producing an activity-dependent hypertrophy of these brain regions. Although dopamine receptor-blocking drugs can suppress tics and have long suggested the presence of supersensitive
dopamine receptors, postmortem binding studies of dopamine receptors failed to provide support for this hypothesis. Positron emission tomography (PET) studies have provided inconsistent evidence for increased dopamine storage and release in striatum.

An immune hypothesis proposes that TS is sometimes caused by infection with β-hemolytic Streptococcus, as seen in children who develop Sydenham chorea. Known as a pediatric autoimmune neuropsychiatric disorder associated with streptococcus infections (PANDAS), evidence for this proposed etiology for a small minority of TS patients has been inconsistent and controversial.

As defined by DSM-5, a tic is a sudden, rapid, recurrent, nonrhythmic motor movement or vocalization. Tics range from intermittent simple brief jerks (simple tics) to a complex pattern of rapid, coordinated, involuntary movements (complex tics) arising abruptly from a background of normal activity and often preceded by a vague, unpleasant sensation that is relieved by the movement (Video 74.1). Although tics usually can be suppressed for a short time, the inner sensation builds relentlessly, producing a burst of tic behavior when the patient stops suppressing them. Tics usually begin in the face (eye blinking, grimacing), neck (head shaking), and shoulders (shrugging), but they can also begin with sounds (sniffing, throat clearing, barking, words, or parts of words). They can progress to involve the thorax and limbs and foul utterances (coprolalia). Repeating sounds (echolalia) or movements (echopraxia) are sometimes seen. The speed of tics ranges from very fast (clonic tics) to sustained contractions (dystonic tics). Simple clonic tics resemble essential myoclonus, and the two conditions are difficult to distinguish. Dystonic tics need to be differentiated from primary torsion dystonia. Sydenham chorea is distinct in manifesting as a continuous restless type of movement pattern, and it is self-limited. Premonitory sensations, intermittency, and suppressibility help distinguish tics from most other movement disorders.

Behavioral or psychiatric symptoms are present in 90% of patients with TS and may be considered part of the clinical syndrome. Impulse control problems are common and can present as aggressivity, rage attacks, antisocial or inappropriate sexual behavior, or self-injury. Obsessive-compulsive symptoms associated with tics overlap with those seen in non-tic-related OCD but are less likely to manifest as compulsive washing or cleaning rituals and more likely to be characterized by obsessions with symmetry, the need to do and redo activities, and “just right” perceptions. Some complex tics can resemble compulsions. Attentional difficulties often precede the appearance of tics by several years and usually reflect coexisting Attention deficit hyperactivity disorder (ADHD) but may also be attributable to other factors such as cognitive fatigue from the effort to suppress tics, obsessions like mental counting, or mood disorders. TS patients have higher rates of sleep disturbances including difficulty falling asleep and staying asleep and have increased sleep latencies and arousals on polysomnography. Tics can persist during sleep, in contrast to most other hyperkinetic movement disorders, usually in an attenuated form. Alterations in sleep and wakefulness patterns may be intrinsic to the disease itself or may be caused by medications used to treat tics and comorbid conditions.