To test the specificity of phenomenological criteria for Functional Tic-Like Behaviours (FTLBs). 

In 2022, the European Society for the Study of Tourette Syndrome criteria for the clinical diagnosis of FTLBs were published, based on expert consensus. They included three major criteria - age at symptom onset ≥12yr, rapid evolution of symptoms, and specific phenomenology.

Children and adolescents with primary tic disorders (PTD) have been prospectively included in a Registry in Calgary, Canada, since 2017. Using the Yale Global Tic Severity Scale, we assessed how many youth with PTD met specific phenomenological criteria for FTLBs at their first clinical visit, to determine their specificity. The phenomenological criteria assessed were: (1) the presence of 1 or more specific complex motor tics commonly seen in FTLBs, including complex arm or hand movement, self-injurious behaviour, blocking, copropraxia; (2) 1 or more specific complex vocal tics commonly seen in FTLBs, including words, phrases, disinhibited speech, coprolalia; (3) having a greater number of complex than simple tics. To avoid bias, we used data collected before 2020.

Of 156 participants included in the Registry between 2017 and 2020, 49 had their first visit at age 12 or older. 14/49 (28.6%) had at least one of the specified complex motor tics. 3/49 (6.1%) had at least one of the specified complex phonic tics. No participants had both specified complex motor and phonic tics. Three of 49 (6.1%) adolescents had more complex than simple tics, 1 (2.0%) had an equal number, and 45 (91.8%) had predominantly simple tics.

Within a sample of adolescents diagnosed with a PTD before 2020, we found that the specificity of phenomenological criteria for FTLBs, including exhibiting specific complex motor and phonic tics, and having more complex than simple tics was very high, at 100% and 92% respectively.