Tic Disorders and Tourette Syndrome
Adrian Sandler
I. Description of the problem.
A. Definitional issues.
1. Tourette syndrome (TS).
TS is a disorder with multiple motor tics and one or more vocal tics (not necessarily concurrently), lasting a period of at least 1 year, in which the individual is never tic-free more than three consecutive months.
The tics may change in nature and severity, and are associated with distress or impairment in function.
Onset is before age 18 years, with peak onset around 5 to 8 years.
Although there is wide variability in symptoms and clinical course, there is a tendency for severity to peak around 9 to 11years, with improvement or even resolution during puberty.
2. The tic disorder spectrum.
Transient tic disorders include single or multiple motor and/or vocal tics, lasting at least 4 weeks up to 12 months.
Most transient tics are simple rather than complex and they do not usually cause great distress. A child with complex and distressing motor and vocal tics lasting a few months may be at risk for developing TS.
Chronic tic disorders are single or multiple motor or vocal tics that last more than a year. It is thought that these disorders share the same pathogenesis and occur on a spectrum.
B. Epidemiology.
1. Prevalence of tic disorder spectrum.
Simple tics are very common in childhood. The 3-month prevalence is 4.3% in boys and 2.7% in girls, and 6% to 13% of all children will experience a transient tic at some time during childhood.
The childhood incidence of chronic tic disorder is around 1% to 2%, with approximately 3:1 ratio of boys to girls.
TS is less common, with prevalence around 3 per 1,000 in 6- to 17-year-olds, based on the 2007 NSCH (National Survey of Children’s Health) survey. TS was twice as likely for teenagers than for preteens, and the ratio of boys to girls was 3:1.
White children were twice as likely as black and Hispanic children to have TS, but there were no differences by parental education or household income.
2. Comorbidity of TS with obsessive-compulsive disorder (OCD) and attention-deficit/hyperactivity disorder (ADHD).
More than 50% of children with TS have extensive obsessions and/or compulsions, and 40% meet criteria for OCD. More than 20% of all children with tic disorders have OCD. Conversely, 18% of children with OCD also have a concurrent tic disorder.
Among all children previously diagnosed with TS, 64% had been diagnosed in the past with ADHD. Fifty percent of all children with tic disorders have ADHD.
Children with TS are 3 to 4 times as likely to have ADHD and 11 times as likely to have OCD as children without tic disorders.
Among all children with TS, clinical depression (36%), anxiety (40%), developmental problems (28%), and learning difficulties (80%) are common.
Sixty percent of children with Asperger syndrome have a tic disorder at some time during childhood.
C. Etiology/contributing factors.
1. The genetics of tic disorders and TS.
Twin studies show fairly high heritability, but there are clearly nongenetic factors influencing phenotypic expression. Linkage studies and genome-wide association studies have indicated signals on chromosomes 2p21, 17p, 8q, and 11q, but to date no single candidate gene has been identified. Other lines of evidence suggest several vulnerable
genes plus environmental stressors causing increased fetal sensitivity in regions of the developing brain. Similar genetic and nongenetic factors appear to be operating in OCD.
2. The neurobiology of tic disorders and TS. Specific cortico-striato-thalamo-cortical circuits have been implicated because of their role in initiating and inhibiting psychomotor activity and in harm detection/avoidance. Emotional (limbic), cognitive, and motor circuits function in integrated ways to suppress behaviors triggered by internal and external stimuli. In patients with TS, fastspiking inhibitory (FSI) interneurons in caudate and putamen are decreased, and inhibitory striatal GABAergic (gamma-aminobutyric acid) networks may be deficient. Cortical disinhibition may be related to hypersensitivity of dopamine D2 striatal receptors.
II. Making the diagnosis.
A. Signs and symptoms.
1. What is a tic?
Tics are more easily recognized than precisely defined. They can be described as rapid, coordinated, isolated fragments of normal motor or vocal behaviors. Tics can be easily mimicked and sometimes are confused with normal behavior.
Motor tics are typically brief, nonrhythmic, repetitive movements of eyes, face, neck and shoulders, with eye blinking, facial grimacing, and head jerking the most common. Vocal or phonic tics may commonly include repetitive throat clearing, sniffing, grunting, or barking.
Tics may be described in terms of location, number, frequency, and duration. They may also be characterized by their intensity, forcefulness, and complexity. Although tics are most commonly simple (brief and meaningless), they may be complex (longer and more elaborate). A few specific terms have been used to describe particular recognizable kinds of tic, such as palilalia (repeating others), coprolalia (uttering obscenities), and copropraxia (making obscene gestures).
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