Challenging current diagnostic and classification criteria for primary tic disorders

Background: Persistent motor and vocal tic disorders (PMTD/PVTD) are distinct diagnoses from Tourette syndrome (TS). In both, the threshold for the diagnosis is up to age 18, whereas tics infrequently manifest after age 12. Methods: In our cohort of youth with tic disorders from Calgary, Canada, we aimed to determine whether the clinical features and comorbidity profile of PMTD/PVTD differ from those of TS, and assess whether chronic tic disorders with adolescent-onset (age≥12) are different from disorders with childhood-onset (<12yr). Results: A total of 341 children and adolescents with primary chronic tic disorders were included (90.0% with TS, 7.0% with PMTD, 1.8% with PVTD). Regarding age at tic onset, participants with adolescent-onset tics (6.7%) were diagnosed with attention-deficit/hyperactivity disorder (ADHD) more often than those with childhood-onset (p=0.02); there were no differences in sex ratio, tic severity and impairment. Regarding tic disorder diagnosis, participants with PMTD/PVTD had a later age at tic onset than those with TS (p=0.01) and had less psychiatric comorbidity (p=0.01), specifically ADHD and obsessive-compulsive disorder; there were no differences in tic severity or impairment. Conclusions: Given that the major difference between TS and PMTD/PVTD lies in psychiatric comorbidities, which are not part of the diagnostic criteria, we suggest creating a single category for primary persistent tic disorders. Tic onset in adolescence is uncommon, and coupled with the lack of any major difference in clinical features, should lead us to question whether the age limit in the diagnostic criteria might not be more relevant as a supportive criterion.