In this study we precisely defined CTs as short lasting mental acts which had the equivalent among complex vocal tics such as coprolalia, echolalia, palilalia, counting and repeating of words or phrases. In such diagnosed group, we found that cognitive tics occurred in more than 1/5 of the patients, they correlated significantly with tic severity and also with some psychiatric comorbidities, especially anxiety disorder and significant social skill problems.
We formulated a hypothesis that particular mental phenomena reported by certain GTS patients may be a form of tic manifestation and we juxtaposed it with the theory that these symptoms are a representation of another psychopathology. Inferring from the positive correlation between CTs and YGTSS (Tables 4, 6), we consider that higher tic severity may increase the risk of CTs’ appearance. The opposite situation, when CTs add significantly to the impairment caused by tics, is less likely because CTs themselves are perceived by patients as egosyntonic and never reported as particularly troublesome and hence they do not require additional or more intensive treatment. Additionally, correlation between premonitory urges and CTs, which emerged statistically significant in univariate analysis, provides further evidence validating the hypothesis of CTs’ affiliation to tic spectrum. Premonitory urges, which exclusively occur in tic disorders, rendered to be associated with CTs especially in children group, nevertheless, also in adult group values reached borderline significance (Table 3). Based on the association of CTs with tic severity and premonitory urges preceding tics, we prone to classify the examined phenomena as the tic spectrum symptoms rather than recognize them as a manifestation of OCD or another psychopathology. There is a possibility of CTs’ occurrence in both patients suffering from the vocal equivalent as well as in those who do not present symptoms of this kind. Echophenomena (pali- and echolalia), coprolalia and counting were most commonly presented in a form of vocalisation, nevertheless, this subgroup did not considerably outnumber the subgroup of patients who experienced analogous symptoms mentally. Moreover, both variants, vocal and cognitive, of a given tic do not necessarily appear in one particular individual, and CT accompanies its vocal equivalent in less than half of cases (Table 2). These observations indicate only a certain degree of relationship between the mental and vocal forms of the tic. As vocal echophenomena, coprolalia and counting are more frequently reported by patients with CTs, we can only speculate that the presence of these vocal tics can increase the risk of its mental equivalent’s occurrence or the situation is exactly the opposite.
Nevertheless, the affiliation of CTs to the tic spectrum should be made with caution because of the correlation between the CTs and psychiatric disorders (Tables 3, 5). With regard to OCD, it should be mentioned that the difference in the number of patients in both groups: with OCD and with YGTSS score evaluated, could have certain impact on the results of these analyses. Moreover, the same type of statistical analysis pointed that CTs tend to co-occur with depression and anxiety (Tables 3, 5), which are closely related to OCD. The concomitance of CTs with depression, which is one of the most common consequences of OCD, and anxiety, which is a typical consecution of obsession and often a causative factor of compulsion, necessitate consideration of whether they represent a collective spectrum of symptoms. The fact that the age of CT onset falls in most patients in early adolescence, a period when tics begin to subside and after the peak tic severity seen usually between 10–12 years (20), also suggests that tic severity does not have to be the crucial factor regarding CTs’ appearance. Furthermore, the logistic regression analysis pointed to a correlation between CTs and significant social skill problems (p = 0.050, Table 4), which are the principal feature of ASD. Due to the lack of sufficient number of patients with the ASD diagnosis, we presumed significant social skill problems to be the principal feature of autistic traits in our group of patients. Significant social skill problems are one of the criteria which have to be met during the ASD diagnosis, thus their presence may enforce the cooccurrence of ASD in GTS patients in our study. On the other hand, they should be considered as an ASD equivalent with caution, as they can also appear independently, and further diagnostic tests could not confirm the suspicion of ASD. Notableness of the association between CTs and significant social skill problems arises from the fact that on its basis it can be hypothesized that CTs may be a form of stereotypic mental act resembling motor stereotypy observed in patients with ASD. As there was no systematic assessment of autistic traits in our cohort, this finding should be considered as a promising hypothesis, which should be confirmed in a study with a larger group of high-functioning autistic patients with preserved communication skills. Another evidence which enforces the theory about the complexity of CTs’ pathogenesis is the correlation of current CTs with current anxiety disorder, established in logistic regression analysis (p = 0.028, Table 6). This information, in addition to association of CTs with lifetime significant social skill problems in multivariate analysis (Table 4) and supported by univariate analyses correlations of these mental phenomena with current OCD (Table 5) and lifetime depression (Table 3), prompt us to suspect that psychiatric comorbidities are a crucial factor in CTs’ prevalence.
We also hypothesized that patients’ age could be a variable associated with the rate of CTs. Age of CTs onset falls during adolescence in most patients although it may occur at any time during the course of the disease. There is an evident association between the prevalence of this mental phenomenon and the age of the patient established in one-way analysis of variance (Tables 3, 5). Even though the multivariate analysis did not demonstrate the same statistical correlation, the borderline values of the significance were reached (in lifetime CTs p = 0.089, in current CTs p = 0.056, Tables 4, 6). The fact that CTs appear several years after the development of the first tic suggests that most individuals do not present with CTs. We also found that CTs occurred in adult patients twice as often as in children. It is possible that younger patients actually report CTs to a lesser extent than older individuals, much like premonitory urges (21, 22), or that CTs may have natural tendency to manifest over time. However, it may also indicate difficulty in obtaining information from younger children and that the diagnostic material collected from children is less reliable because of the children’s incomprehension of the questions during the interview and the lack of parents’ insight into child’s mental state. Taking into consideration the fact, that CTs were never reported spontaneously by patients and were realized only due to active inquiry, the proper cooperation and communication appear essential in diagnosing these phenomena. The acknowledgment of this may contribute to the understanding why the issue of CTs is still not sufficiently examined as the majority of studies in GTS involve child population.
We found significant differences in correlates of CT’s in children and adults group. In logistic regression model in children, age at evaluation was a factor significantly associated with lifetime CTs (p = 0.033), whereas in adults there were no statistically significant predictors of lifetime CTs. For current CTs, none of the variables reached statistical significance in children, while anxiety disorder was a predictor of current CTs in adults (p = 0.018). These differences between children and adult patients with GTS can provide with noteworthy conclusions regarding the pathogenesis of these symptoms. Taking into consideration the fact that certain co-occurring disorders have the tendency to be present in the specific age groups (Table 1), we can speculate that whole group of symptoms, depending on the age of the patient, can be a factor which could be related to CTs’ appearance. In this case CTs would have various causes, distinct for age groups and specific for particular patients. Thereby, the differences in clinical picture of children and adults groups provide further evidence that pathogenesis of CTs’ is complex, depends on multiple factors and is related to phenotypic variability of GTS.
Another possible consideration of CTs character arises from the careful understanding of its definition: CTs are pleasant or neutral, stimulating in their nature rather than regulating negative emotional states. Current research emphasizes two main basic human needs that should be taken into general consideration in describing and understanding psychiatric phenomena: regulation of negative emotional states and reward seeking (stimulation) (23, 24). Importantly, these needs may be addressed with different strategies (mature or immature, short or long-term, conscious or unconscious, constructive or destructive). A commonly used regulative/reward-seeking strategy is the use of psychoactive substances like for instance alcohol or stimulants. Although GTS is associated with a decreased risk of substance use disorders with the prevalence of 6.2%, it seems to be related to overrepresentation of children in research sample groups. Substance abuse is significantly higher among adults compared to adolescents and children: 18.5% vs 2.6% vs 0.0%, respectively, with the median age of onset of 16 years (2). In the cohort of 141 adult patients with GTS reported by Haddad, more than ¼ of them developed alcohol or drug abuse (25). However, substance use disorders were more prevalent among individuals with comorbid OCD and ADHD (2, 25) in comparison to GTS without these comorbid disorders. Plausibly, in GTS, while comorbidity with OCD or ADHD is present, alcohol or other substances may be more likely used to reduce tics, serve as self-medication and provide stimulation. It can be very carefully speculated that CTs may in some cases act like an internal stimulatory, immature mechanism, while obsessions may act as an internal, immature regulatory (short-term) strategy. CTs may be stimulating (4), so in those patients they may encourage autostimulation. The certain evidence which encourages this hypothesis is similar age of onset of substance use disorders reported by Hirschtritt et al. (2) and CTs found in our study (median: 16 and 13.5, respectively). The prevalence of alcohol or substance use disorder was not assessed in our study, yet it would be important and interesting to address this issue in future studies and to investigate whether presence of CTs may serve as protector or rather as a risk factor of substance use in GTS and other clinical and non-clinical samples.
The value of performed study arises from both extending of scientific knowledge in the topic of mental phenomena in patients with GTS and prospective clinical application of acquired data. In opposition to OCD, CTs do not require treatment as are perceived by patients as neutral and egosyntonic. It also seems important to pay attention to the presence of mental phenomena resembling tics which do not fulfill current diagnostic criteria of this hyperkinetic movements and, although unobservable, may belong to the spectrum of tic phenomenology. Our results suggest that GTS-affected patients who also have CTs at the time of examination should be carefully evaluated for the existing anxiety disorders and more severe tics. This could certainly influence the choice of appropriate treatment.
There are several limitations to our study which include: lack of control group; lack of any validated instrument in CTs’ assessment; the established CT definition limited to tic phenomenology with exclusion of overlapping, long-lasting mental phenomena from OCD spectrum; recall bias that could potentially influence the reported prevalence rate and age at onset of CTs; the one-time registration study design that could influence the rate of CTs and psychiatric comorbidities; referral bias as the patients were evaluated by neurologist and the cases with more severe psychopathology were referred to psychiatric clinics, which explains low numbers of OCD and depression in children group, as well ASD in all GTS group.