Tourette

Tourette syndrome Classification Characteristics Causes Diagnosis Screening Management Prognosis Epidemiology History and research directions

Epidemiology

Tourette syndrome is found among all social, racial and ethnic groups,[3][65] has been reported in all parts of the world,[66] and is three to four times more frequent among males than among females.[67] The tics of Tourette syndrome begin in childhood and tend to remit or subside with maturity; thus, a diagnosis may no longer be warranted for many adults, and prevalence is much higher among children than adults.[26] Children are five to twelve times more likely than adults to be identified as having tic disorders;[68] as many as 1 in 100 people experience tic disorders, including chronic tics and transient tics in childhood.[3]

Discrepancies across current and prior prevalence estimates come from several factors: ascertainment bias in earlier samples drawn from clinically referred cases, assessment methods that may fail to detect milder cases, and differences in diagnostic criteria and thresholds.[69] There were few broad-based community studies published before 2000 and until the 1980s, most epidemiological studies of Tourette syndrome were based on individuals referred to tertiary care or specialty clinics.[1][70] Children with milder symptoms are unlikely to be referred to specialty clinics, so these studies have an inherent bias towards more severe cases.[1][71] Studies of Tourette syndrome are vulnerable to error because tics vary in intensity and expression, are often intermittent, and are not always recognized by clinicians, patients, family members, friends or teachers;[6][72] approximately 20% of persons with Tourette syndrome do not recognize that they have tics.[6] Recent studies—recognizing that tics may often be undiagnosed and hard to detect—use direct classroom observation and multiple informants (parent, teacher, and trained observers), and therefore record more cases than older studies relying on referrals.[73][51] As the diagnostic threshold and assessment methodology have moved towards recognition of milder cases, the result is an increase in estimated prevalence.[69]

Tourette syndrome was once thought to be rare: in 1972, the US National Institutes of Health (NIH) believed there were fewer than 100 cases in the United States,[74] and a 1973 registry reported only 485 cases worldwide.[75] However, multiple studies published since 2000 have consistently demonstrated that the prevalence is much higher than previously thought.[76] The emerging consensus is that 1–10 children per 1,000 have Tourette's,[2] with several studies supporting a tighter range of 6–8 children per 1,000.[4] Using year 2000 census data, a prevalence range of 1–10 per 1,000 yields an estimate of 53,000–530,000 school-age children with Tourette's in the US[4] and a prevalence range of 6–10 per 1,000 means that 64,000–106,000 children aged 5–18 years may have Tourette's in the UK.[51] Most of these children are undiagnosed and have mild symptoms without distress or impairment.[