There’s not enough data for accurate estimate of Tourette Syndrome incidence

Hot off the presses is “Prevalence of Tic Disorders: A Systematic Review and Meta-Analysis,” an article published in the journal Paediatric Neurology by several physicians, including Dr. Tamara Pringshiem.

Dr. Pringshiem is a member of the Tourette Syndrome Foundation of Canada’s Professional Advisory Board. The TSFC community has the chance to hear Dr. Pringshem speak at the upcoming National Conference in October, when she will present on the latest treatment guidelines for TS.

Dr. Pringshiem’s recent article focuses on the problem of underdiagnosis of TS and other tic disorders. The underdiagnosis of TS is a complex issue. Many people with TS are unaware that they have the condition. One study even puts the percentage of people who do not know they have TS at 30 percent.

Tics can, and often are, suppressed or disguised in public. Additionally, they often decline with age. On top of that is the problem of people hiding the fact that they have TS because of fear of social stigma. All these factors combined make it extremely difficult to get an accurate estimate of the prevalence of the condition in the Canadian population.

Rather than relying on one or two studies to establish the current prevalence, Dr. Pringshiem and her colleges examined several different incidence studies in order to obtain the most accurate estimate possible. Their main findings were:

  • Tic disorders, including TS, are more common among children than adults; and more common among males than females.
  • Tic disorders are more common in special education settings, among those receiving institutionalized care, and among those with Autism.
  • The most common type of tic disorder is transient tic disorder (approximately 2.99 percent), followed by chronic tic disorder.
  • TS is the third most common tic disorder.
  • There is no consensus among experts about the prevalence of TS and other tic disorders.
  • According to most school-based studies, 2 to 11 people out of every 1000 have TS.
  • The highest numbers, reported in three academic studies, put the incidence of TS at 3.8 percent. The lowest reported prevalence was 0.1 percent.
  • Very few studies focus on figuring out how many adults have TS.
  • Because the definition of TS has changed over time, prevalence hasn’t been consistently measured from study to study.
  • There is no current Canadian prevalence data; instead, incidence studies primarily focus on American and Western European populations.

Dr. Pringshiem and her colleagues recommend more studies on the prevalence of TS and other tic disorders. They also argue for the simplification of how we classify tic disorders. Making TS, chronic motor tic disorder, and chronic vocal tic disorder separate and distinct conditions, Pringshem et al. contend, is of “debatable value” because there are so few differences in the conditions and in how they are treated.

Perhaps as the TS community is more and more successful at eliminating stigma, more people will feel comfortable being “out” about their condition. As we as a country become more aware of the condition, those who do not know they have TS will come to understand why they do what they do.

In time, perhaps, new studies may come to better understand the actual prevalence of condition in Canada. For now, we have to make do with only a few studies of the U.S. and Europe and try to remember that the actual prevalence of TS is likely much higher than our best guess.

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