Is Persistent Motor or Vocal Tic Disorder a Milder Form of Tourette Syndrome?

Abstract

Background: Persistent motor or vocal tic disorder (PMVT) has been hypothesized to be a forme fruste of Tourette syndrome (TS). Although the primary diagnostic criterion for PMVT (presence of motor or vocal tics, but not both) is clear, less is known about its clinical presentation.

Objective: The goals of this study were to compare the prevalence and number of comorbid psychiatric disorders, tic severity, age at tic onset, and family history for TS and PMVT.

Methods: We analyzed data from two independent cohorts using generalized linear equations and confirmed our findings using meta-analyses, incorporating data from previously published literature.

Results: Rates of obsessive-compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD) were lower in PMVT than in TS in all analyses. Other psychiatric comorbidities occurred with similar frequencies in PMVT and TS in both cohorts, although meta-analyses suggested lower rates of most psychiatric disorders in PMVT compared with TS. ADHD and OCD increased the odds of comorbid mood, anxiety, substance use, and disruptive behaviors, and accounted for observed differences between PMVT and TS. Age of tic onset was approximately 2 years later, and tic severity was lower in PMVT than in TS. First-degree relatives had elevated rates of TS, PMVT, OCD, and ADHD compared with population prevalences, with rates of TS equal to or greater than PMVT rates.

Conclusions: Our findings support the hypothesis that PMVT and TS occur along a clinical spectrum in which TS is a more severe and PMVT a less severe manifestation of a continuous neurodevelopmental tic spectrum disorder. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Keywords: Tourette; chronic tics; meta-analysis; severity.

FIG. 1

Yale Global Tic Severity Scale (YGTSS) Motor and YGTSS Vocal tic severity subscale scores in individuals with persistent motor and vocal tics (PMVT) versus Tourette syndrome (TS) in the Tourette Association of America International Consortium for Genetics (TAAICG) (A,B) and (OCGAS) (C,D) samples. Note that only PMVT participants with motor tics were included in the YGTSS Motor tic severity subscale analysis, and only PMVT participants with vocal tics were included in the YGTSS Vocal tic severity subscale analyses.

FIG. 2

Ages of onset of tics and comorbid psychiatric disorders in persistent motor and vocal tics (PMVT) versus Tourette syndrome (TS). Ages of onset are arranged in chronological order. Left panel, Tourette Association of America International Consortium for Genetics (TAAICG) sample. Right panel, OCD Collaborative Genetics Association Study (OCGAS) sample. ADHD, attention deficit hyperactivity disorder; OCD, obsessive–compulsive disorder. [Color figure can be viewed at wileyonlinelibrary.com]

FIG. 3

Forest plots comparing the prevalence of psychiatric comorbidities (A–F), age of tic onset (G) in individuals with persistent motor and vocal tics (PMVT) and Tourette syndrome (TS), and proportion of individuals with pure motor tics (H) stratified by sample size. ADHD, attention deficit hyperactivity disorder; CI, confidence interval; OCD, obsessive–compulsive disorder; OR, odds ratio. [Color figure can be viewed at wileyonlinelibrary.com]