Functional tic-like behaviors

Various authors have identified differences in the frequency or character of premonitory phenomena (premonitory urges, PUs) as a potential feature that can discriminate functional tic-like behaviors (FTLB) from primary tic disorders \citep{36362696,Martino2023}. The frequency of PUs in those prior reports differed to a clinically important degree from the frequency in typical tic patients at a similar disease duration \citep{37224324}. However, prospectively comparing 83 patients with typical tics and 40 with FTLB from the Calgary tic registry, Szejko and colleagues found no significant differences in premonitory urge severity (PUTS scale total score) nor in any of the individual PUTS items \citep{Szejko_2023}. The authors noted that their results are supported by other reasonably large case series \citep{36203825,34824091}, and provide a brief but compelling discussion of potential implications.
Clinical differences between functional tics and neurodevelopmental tics were confirmed in a study by \citet{Cavanna2023}. In this study, 105 consecutive patients who had developed functional tics in the period April 2020 to March 2023 were examined with a neuropsychiatric assessment. Besides the (sub)acute onset and high frequency of complex movements and vocalizations, it was shown that 23% had a pre-existing tic disorder, 70% had comorbid anxiety, 40% had a comorbid affective disorder, and 41% had at least one other functional neurological disorder. The same group directly "compared the clinical features of patients who developed functional tics during the COVID-19 pandemic (N = 83) to patients with Tourette syndrome matched for age and gender (N = 83)" \citep{37421881}. This comparison identified many variables previously reported to differ between the two groups, but the statistically strongest indicators were "tic-related obsessive-compulsive behaviors" and a family history of tics, both of which were much more common in typical TS. Another interesting study was published by the same group of authors \cite{Cavanna2023a}. This time, authors compared 66 patients with FTLB with 44 patients with different functional movement disorders (dystonia, tremor, gait disorder and myoclonus). While both groups shared some similar characteristics such as female preponderance, comorbid anxiety, depression and other functional neurological symptoms and subacute onset of symptoms, patients with FTLB had earlier age of symptom onset, were more frequently exposed to social media. 
 \cite{Fremer2024} published another study focused on differences between patients with tics and FTLB. 32 patients with FTLB were compared with very large sample of patients with tics (n=1032). A number of previously listed characteristic of FTLB group were replicated: older age of onset, higher prevalence of females, higher rate of obsene and socially inappropriate behaviors. Interestingly, FTLB patients had significantly lower rates of typical psychiatric comorbidities that occur in TS (ADHD and OCD). Phenotypic differences between these two group of patients were also analyzed by group of researchers from Denmark \cite{Andersen2023a}. 53 FTLB patients were compared with 200 patients with tics. Patients with FTLB were found to have more complex tics, were older at symtom onset, were more frequently females, and had less frequently positive family history of tics. Some new findings were also reported in this study: patients with FTLB had more family members with psychiatric comorbidities, had more common history of trauma preceding the onset. 
 
\cite{Firestone2022} published report about cluster of cases of FTLB that surged in the school in Minnesota. This most likely was the case of what was previously described in the literature of the mass sociogenic illness \cite{M_ller_Vahl_2021a}. Eight students of the same school developed FTLB, all of them were female at the age of 15-17. Following previous line of research, all of them had history of depression or anxiety.
 As noted above, patients with TS are not immune from also developing functional tic-like behaviors (FTLB). This association is not surprising, as for example pseudoseizures are more common in people with epilepsy. \citet{M_ller_Vahl_2023} present data on 71 TS patients whom they also diagnosed with FTLB. A majority (56%-79%) had psychological features common in people with other functional symptoms, and about a third of them had a history of other medically unexplained symptoms; these findings suggest that the cause of FTLBs is likely similar to that of other functional neurological symptoms. The authors comment that their ability to identify a fairly large sample of TS+FTLB suggests that clinicians faced with treatment-resistant symptoms in TS should consider whether the symptoms are FTLB rather than tics.
Diagnostic agreement in assessing FTLB was examined by asking eight experts in diagnosing and treating patients with tics to evaluate videos from 24 adults and diagnose them with either functional tics, primary tics or both \citep{Rigas2023}. The diagnostic agreement was fair based on phenomenology alone, and increased to moderate when additional clinical information was provided. The diagnostic distinction between primary and functional tics is shown to be difficult in the absence of clinical information.
Two groups have reported about long-term prognosis in patients with FTLB \cite{Nilles2024,Prato2022a}\cite{Prato2022a} found that at 12 month follow up both tics as well as anxiety significantly improved while OCD and depressive symptoms persisted. \cite{Nilles2024} observed meaningful improvement of FTLB over a period of observation of 12 months indicating that they overall have good prognosis. 

Comorbidities

A survey in children with tic disorders led to a predictive model for "behavioral problems" (based on the CBCL) \citep{36732748}.
\citet{Sadeh2023} examined the presence of depressive symptoms in a cohort of 85 children and adolescents with chronic tic disorders (CTD), aged 6-18 years, with the Child Depression Inventory. In total, 21% had depressive symptoms and the presence of depressive symptoms was correlated with the presence of comorbid OCD and/or ADHD. Furthermore, symptoms of depression moderated the correlation between tic-related impairment and tic severity. Therefore, the authors suggest that it is important to screen and treat depression in children with CTD. 
The presence of depression and anxiety were assessed in several other studies. \citet{Isaacs2023} examined a population of 120 adult patients with CTD with several scales as part of routine care. Symptoms of anxiety were more common than depressive symptoms. Anxiety, depressive and OCD symptom severity were significantly associated to each other, but not to tic severity. In a systematic review and meta-analysis including twelve studies from 1997-2022,  the prevalence of anxiety and depression was found to be 36.4 % and 53.5 % respectively \citep{Abbasi2023}.
Impulsivity and attention were compared in 14 patients with TS, 16 patients with OCD and 28 healthy controls \citep{Koenn2023}. Both patients with OCD and patients with TS showed significant deficits in attention via self-assessment. The severity of tics was correlated strongly positively with attentional impulsivity. The authors conclude that a detailed interpretation of the various tools for measuring impulsive behavior is necessary.
Topic of sleep problems in TS was explored by \cite{Colreavy2023}. Interestingly enough, they found that sleep patterns in children with TS were more impacted by the pandemic than in typically developing children. \cite{Keenan2024} adopted naturalistic, longitudinal approach to examine sleep in children with TS. Importantly, TS children were compared to healthy controls. In addition to clinical assessment, authors attributed variety of scales and measured sleep-wake cycle with wrist actigraphy. As a result, it has been demonstrated that children with TS spent significantly more time in bed, have increased sleep onset latency, reduced sleep efficiency, lower subjective sleep quality, whereas sleep time was comparable. In contrast to clinical observations, self-reported tic severity was not related to increased sleep onset latency. In addition, 83.33% of children with TS fulfilled the diagnostic criteria for a sleep disorder highligting importance for screening for sleep difficulties in clinical routine. 
 
Kurvits et al. \cite{Kurvits2023} investigated investigated the prevalence of prevalence of compulsive sexual behaviors and paraphilic interests in patients with tics. In contrast to previous reports, these comorbidities were found with the same rate as in general population. There was also no association with use of antipsychotics. ADHD was risk factor for paraphilic interests and compulsive sexual behaviors in TS.  
 
TS Study Group from Denmark \cite{Andersen2023} published results of longitudinal study in which correlates of subtance use of pediatric patients with TS. Presence of ADHD and lower socioeconomic status of the guardian predicted higher risk for tobacco smoking, while coexisting OCD was a protective factor. The same group \cite{Tygesen2023} compared fine motor skills in children with TS, their healthy siblings and matched healthy controls. No difference between these three groups were found.