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
Important study was published by the group from the Hannover Medical School \cite{Brandt2023}. The authors investigated the nature of the non-just-right experiences (NJRE) that have been previously linked both to premonitory urge as well as OCD. 111 TS patients completed both the PUTS as well as the revised non-just-right experiences scale (NJRE-QR), and questionnaires regarding their tic severity, and comorbid OCD/OCB. NJRE were more related to the OCD spectrum than premonitory urges and tics. The same group \cite{Brandt2023a} examined whether clinical characteristics of premonitory urges in a large cohort of patients with chronic tic disorders. PU and tic severity were associated and in vast majority of patients tics were followed by urge relief. Some risk factors for the presence of PU were identified: factors for the presence of PU were identified, being ADHD, depression, female gender and older age. On the contrary, OCD and younger age were associated with higher urge intensity.
Larsh et al. \cite{Larsh2023a} used a combined approach to determine whether cortical properties such as excitability (CE) as well as cortical inhibition (LICI) correlate with urges and tics. In line with previous studies, urge intensity correlated with tic scores. Higher urge severity correlated with lower CE and 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 \cite{Kimura2023} explored the pre-movement gating (attenuation) using somatosensory evoked potentials (SEPs). Interestingly enough, sensomonitor processing was preserved for simple tics but impaired for complex tics in a group of individuals after middle adolescence.
Many people with GTS report hypersensitivity to subtle sensory inputs. Marked discomfort from the tag in the neck of a T-shirt, or from the quiet buzz of fluorescent lamps, are classic examples. Careful studies have shown that sensory hypersensitivity (SH) is explained by differences in central processing, e.g. attention, not by the peripheral nervous system (___). \citet{37026772} gathered all reported cases of SH following a stroke (N=8), which had pointed to lesions of the insula. In 3 newly identified cases, the lesions overlapped in the right anterior insula, the claustrum, and the Rolandic operculum.
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}.
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
Background and purpose: Until the outbreak reported during the COVID-19 pandemic, functional tics were considered to be a relatively rare clinical phenotype, as opposed to other functional movement disorders such as functional tremor and dystonia. To better characterize this phenotype, we compared the demographic and clinical characteristics of patients who developed functional tics during the pandemic and those of patients with other functional movement disorders.
Methods: Data from 110 patients were collected at the same neuropsychiatry centre: 66 consecutive patients who developed functional tics without other functional motor symptoms or neurodevelopmental tics and 44 patients with a mix of functional dystonia, tremor, gait, and myoclonus.
Results: Both groups were characterized by female sex preponderance (70%-80%) and (sub)acute onset of functional symptoms (~80%). However, patients with functional tics had a significantly earlier age at onset of functional symptoms (21 vs. 39 years). Exposure to relevant social media content was reported by almost half of the patients with functional tics, but by none of the patients with other functional movement disorders. Comorbidity profiles were similar, with relatively high rates of anxiety/affective symptoms and other functional neurological symptoms (nonepileptic attacks).
Conclusions: Patients who developed functional tics during the pandemic represent a phenotypic variant of the wider group of patients with functional movement disorders, associated with younger age at onset and influenced by pandemic-related factors, including increased exposure to specific social media content. Diagnostic protocols and treatment interventions should be tailored to address the specific features of this newly defined phenotype.