This study states that Persistent motor or vocal tic disorder (PMVT) is hypothesized to be a forme fruste (milder version) of Tourette syndrome (TS).1, 2 This formulation is reflected in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), where the diagnostic criteria differ only in the requirement that either motor or vocal tics be present in PMVT and that both be present in TS.3 During the planning phase, the DSM-5 committee on TS and tics considered merging these disorders, citing lack of evidence of distinct etiologies.4 Ultimately, the distinct classifications were retained to facilitate research of TS and PMVT separately to provide insights about their phenomenology.

Although tics are the distinguishing feature of TS, 76–90% of those who present for clinical care also have one or more comorbid psychiatric illnesses,5-8 which contribute to the observed phenotypic heterogeneity of the disorder and have a strong influence on clinical outcomes.9 Attention deficit hyperactivity disorder (ADHD) and obsessive–compulsive disorder (OCD) are the two most common psychiatric comorbidities, and their presence increases the likelihood of potentially impairing symptoms, such as social disinhibition and self-injurious behaviors, other psychiatric disorders, and the use of or need for pharmacological treatment. Despite its close clinical similarity to TS and higher population prevalence, less work has been done to characterize PMVT. In particular, it is unknown whether its clinical presentation, outside of the manifestation of tics, is similar to that of TS, or whether it has different patterns of comorbidities, tic severity, age of onset, or family history.

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