Prognosis and natural history

In a nationwide cohort study in Sweden, 3761 individuals with tic disorders in childhood were included in order to examine the prevalence and risk factors for the persistence of tic disorders  into adult life \citep{37246931}. In total, 20% of children with tic disorder received a chronic tic disorder diagnosis in childhood. The strongest risk factors for persistence were psychiatric comorbidity in childhood and family history of psychiatric disorders.
The prevalence of TS was found to be 1% in a sample of 289 6-year-old children representative for the population of Menorca \citep{Francés2023}.

Sensory phenomena and premonitory urge

In this online study, the authors investigated the nature of  non-just-right experiences (NJRE) that have been previously linked to premonitory urges (PU) as well as to OCD \cite{Brandt2023}. Therefore, 111 patients with TS completed different self-assessments for tics, PU and comorbid OCD/OCB. NJRE were more related to the OCD spectrum than to PU and tics. The same group \cite{Brandt2023a}  examined clinical characteristics of PU in a large cohort of patients with chronic tic disorders (n=291). PU and tic severity were associated. In the vast majority of patients, tics were followed by an urge relief. The following  factors for the presence of PU were identified:  ADHD, depression, female gender, and older age. On the contrary, OCD and younger age were associated with higher urge intensity.   
  \cite{Larsh2023a}    used a combined approach to determine whether cortical properties such as excitability (CE) as well as cortical inhibition (LICI) correlate with PU PU and tics. In line with previous studies, PU PU intensity correlated with tic severity. severity. Higher urge severity correlated with lower CE and LICI. LICI.
Li et al. \cite{Li2023}  published results of the systematic review and meta-analysis investigating relationship between urge severity and neuronal correlates. Altogether, 22 studies were identified with a total of 1236 patients. Results of meta-regression demonstrated that age and tic severity were related to PU severity. From the neuroanatomic perspective, PU was related to the following regions of the brain:  insula, prefrontal cortex, anterior cingulate cortex, and supplementary motor area. 
 A study from Japan explored the pre-movement gating (attenuation) using  somatosensory evoked potentials (SEPs). The authors found that  sensorimotor processing was preserved for simple tics but impaired for complex tics in a group of individuals after middle adolescence.   \cite{Kimura2023} 

Transient effects of environment on tic severity

A fascinating study from Israel examined the timing of tics moment to moment while children with tic disorders watched a movie and played a video game \citep{37946628}. This study involved substantial labor on the part of the researchers. Tics did not occur randomly over time but rather were more or less common across participants during specific moments of the movie clip and when reward was expected in the video game. One interesting hypothesis presented for future study was that "the portrayal of motor actions in movies elicits" an urge to tic. Similarly, one would be very interested in whether movie or game conditions eliciting higher tic rates correspond to greater release of striatal dopamine in people with and without tics \citep{9607763}.
Group from Italy \cite{Prato_2023} explored the impact of SARS-COV-2 infection in children and adolescents with TS. Participants who had COVID-19 infection experienced both short lasting as well as long lasting symptoms (long COVID). Of note, 35% of patients experienced worsening of tics and/or psychiatric comorbidities.  The impact of COVID-19 pandemic on tics was also investigated by (Hall 2022). The authors compared YGTSS pre and during the pandemic. No significant differences between two assessments were found.
In a population-based study, Jack et al. \cite{Jack_2023} reported that the incidence of tics in children and young people increased across all age and sex groups during the COVID-19 pandemic, especially in teenage girls. However, it is feasible to speculate that many of those patients diagnosed with tics  suffered from FTLB, since it is well known that the incidence of FTLB dramatically increased during the pandemic and many of these patients had been misdiagnosed with TS.   
 

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 on this topic was published by Cavanna et al. (2023) \cite{Cavanna2023a} . They compared 66 patients with FTLB with 44 patients with different kinds of functional movement disorders (FMD) (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 as well as subacute onset of symptoms, patients with FTLB had an earlier age of symptom onset and were more frequently exposed to social media than those with other forms of FMD.
Fremer et al (2024)  \cite{Fremer2024} compared a group of patients with FTLB (n=32) with a very large sample of patients with tics (n=1032). A number of previously reported characteristics of FTLB could be replicated: older age of onset, higher prevalence of females, and higher rate of obscene and socially inappropriate behaviors. Interestingly, patients with FTLB had significantly lower rates of psychiatric comorbidities typically seen in TS such as ADHD and OCD. Phenotypic differences between  patients with FTLB (n=53) and tics (n=200) were also analyzed by a group of researchers from Denmark \cite{Andersen2023a} .  Patients with FTLB were found to have more complex symptoms, were older at symptom onset, were more frequently females, and had less frequently a positive family history for tics. As a new finding, they reported that patients with FTLB had more family members with psychiatric disorders and had more common a history of trauma preceding the onset.  In another Danish study,  Okkels et al. (2023) described characteristics of a cohort of patients with FTLB. Again, the majority were females, had mainly complex movements with no rostrocaudal progression. Almost 70% reported harmful behaviors and 96% had exposure to social media \cite{Okkels2023} .
Firestone et al. (2022) \cite{Firestone2022} reported an outbreak of mass sociogenic illness in a school in Minnesota presenting with FTLB similar to the first FTLB outbreak in LeRoy in 2012. Eight students of the same school developed at the same time FTLB, all were female at the age of 15-17 and all 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.
Finally, an international group of experts published results of the so far largest group of patients with FTLB seen in multiple centers across the globe  \cite{Martino2023}. Altogether, 294 patients with FTLB were included. The vast majority were adolescents and young adults (97%), 87% were females, 70% presented with rapid symptom progression, and spontaneous remission was noted in 20% of cases. From the phenomenological perspective, 85% demonstrated complex movements and 81% complex vocalizations. One fifth had a preexisting tic disorder, 66% had anxiety, around 30% depression, 24% autism, and 23%ADHD. Again, a high number (60%) reported exposure to social media.