Prevalence of Tic Disorders: A Systematic Review and Meta-Analysis

Abstract

This study evaluated the prevalence of tic disorders. MEDLINE and EMBASE databases were searched, using terms specific to Tourette syndrome and tic disorders, for studies of incidence, prevalence, and epidemiology. Thirty-five studies reporting data from 1985-2011 on the incidence or prevalence of tic disorders in a defined population were included. One reported incidence, and 34 reported prevalence. Meta-analysis of 13 studies of children yielded a prevalence of Tourette syndrome at 0.77% (95% confidence interval, 0.39-1.51%). Prevalence is higher in boys: 1.06% of boys were affected (95% confidence interval, 0.54-2.09%) vs 0.25% of girls (95% confidence interval, 0.05-1.20%). Transient tic disorder comprised the most common tic disorder in children, affecting 2.99% (95% confidence interval, 1.60-5.61%). Meta-analysis of two studies assessing adults for Tourette syndrome revealed a prevalence of 0.05% (95% confidence interval, 0.03-0.08%). The prevalence of tic disorders was higher in all studies performed in special education populations. Tic disorders are more common in children than adults, in boys than girls, and in special education populations. Parents, educators, healthcare professionals, and administrators should be aware of the frequency with which tic disorders occur, and ensure proper access to appropriate care.

Introduction

Tourette syndrome is a childhood-onset neuropsychiatric disorder with multiple motor tics, and at least one phonic tic that has persisted for at least 1 year. Tics are sudden, stereotyped movements or sounds that are typically performed secondary to irresistible urges. Tourette syndrome is commonly associated with other neuropsychiatric comorbidities, with attention-deficit hyperactivity disorder and obsessive-compulsive disorder comprising two of the most common [1], [2].

The relatively unique features of Tourette syndrome have confounded studies of its epidemiology. The natural history of Tourette syndrome is one of waxing and waning, and tics may change in character, frequency, and intensity over relatively short periods [3]. Although the disorder can persist for life, in many cases, its manifestations largely remit by adulthood [4]. The time course and specific appearance of tics are also largely a function of age. The onset of tics typically occurs between ages 3 and 8 years (mean onset, ages 6 and 7 years), and 93% of patients are symptomatic by age 10 years [5], which is also the reported average age of greatest tic severity [4]. In addition, the disorder demonstrates a strong male preponderance [5]. Comparisons between study populations therefore depend crucially on adequate adjustments for age and sex. Simple tics may be disguised or suppressed [6], and a relatively large percentage of patients with Tourette syndrome (up to 30%) [7] can be unaware of their tics. Tics also occur less frequently in public, and are more pronounced in a “comfortable” environment. These clinical characteristics may lead to underrecognition of the disorder. Many early studies on the prevalence of Tourette syndrome were limited by small samples, case counts based on clinically ascertained individuals, and a lack of systematic methods to identify cases. Together, these features led to underdiagnoses and underestimations of disease rates.

This study was designed to evaluate the prevalence and incidence of Tourette syndrome through a systematic review and meta-analysis of published peer-reviewed studies. This study was part of a larger initiative funded by the Public Health Agency of Canada to facilitate a better understanding of the burden of neurologic illnesses in Canada and worldwide.