Testing the specificity of phenomenological criteria for functional tic-like behaviours in youth with Tourette syndrome

Background and purpose: The aim was to test the specificity of phenomenological criteria for functional tic-like behaviours (FTLBs). The European Society for the Study of Tourette Syndrome (ESSTS) criteria for the diagnosis of FTLBs include three major criteria: age at symptom onset ≥12 years, rapid evolution of symptoms and specific phenomenology.

Methods: Children and adolescents with primary tic disorders have been included in a Registry in Calgary, Canada, since 2017. Using the Yale Global Tic Severity Scale, the proportion of youth with primary tic disorders who met specific phenomenological criteria for FTLBs at first visit was assessed: (1) having ≥1 specific complex motor tic commonly seen in FTLBs, including complex arm/hand movements, self-injurious behaviour, blocking, copropraxia; (2) having ≥1 specific complex phonic tic commonly seen in FTLBs, including saying words, phrases, disinhibited speech, coprolalia; (3) having a greater number of complex tics than simple tics. Children seen for the first time between 2017 and 2019 and between 2021 and 2023 were analysed separately.

Results: Of 156 participants included between 2017 and 2019, high specificity (94.2%) of the age at onset criterion (≥12 years) and of having at least two complex motor behaviours and one complex phonic behaviour at first visit (96.2%) was observed. Some of the complex motor tics had lower specificity. The specificity of the FTLB diagnostic criterion of having more complex tics than simple tics was 89.7%. There was no significant difference in specificity of the criteria for children seen for the first time between 2017 and 2019 and between 2021 and 2023 (n = 149).

Conclusion: This information supports the use of the ESSTS criteria for FTLBs in clinical practice.