Non-invasive assessment of autonomic nervous function in Gilles de la Tourette syndrome

Psychosocial stress in children with Tourette syndrome and chronic tic disorder

BACKGROUND

This study aimed to understand the longitudinal relationship between psychosocial stress with tic exacerbation in children with Tourette syndrome (TS) and chronic tic disorder.

METHODS

Consecutive ratings of tic severity as well as child and parental reports of psychosocial stress were obtained for 373 children (296 males, 77 females; mean age 9y 5mo; SD 3y 3mo) with TS and chronic tic disorder between January 2018 and December 2020. The Yale Global Tic Severity Scale (YGTSS) global severity score, total tic score, and impairment rating were calculated. The stressful events and YGTSS measurements were used and treated as time-varying variables in the analyses. Models that controlled for non-independence among the repeated observations using a random intercept and random slope model were employed. Each participant was treated as a random factor in the modelling.

RESULTS

Family-related stress, personal relationship stress and school-related stress were independently associated with increasing YGTSS global severity, total tic score, and impairment rating over time. An increased number of stressful events were associated with increased severity of tics.

CONCLUSION

Family, personal relationships, and school-related stress were consistently associated with the exacerbation of tics. Managing these stressful events is important in the treatment of TS and chronic tic disorder.

Tics and Emotions

Tics can be associated with neurological disorders and are thought to be the result of dysfunctional basal ganglia pathways. In Tourette Syndrome (TS), excess dopamine in the striatum is thought to excite the thalamo-cortical circuits, producing tics. When external stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, more dopamine is produced, furthering the excitation of tic-producing pathways. Emotional processing structures in the limbic are also activated during tics, providing further evidence of a possible emotional component in motor ticking behaviors. The purpose of this review is to better understand the relationship between emotional states and ticking behavior. We found support for the notion that premonitory sensory phenomena (PSP), sensory stimulation, and other environmental stressors that impact the HPA axis can influence tics through dopaminergic neurotransmission. Dopamine plays a vital role in cognition and motor control and is an important neurotransmitter in the pathophysiology of other disorders such as obsessive–compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD), which tend to be comorbid with ticking disorders and are thought to use similar pathways. It is concluded that there is an emotional component to ticking behaviors. Emotions primarily involving anxiety, tension, stress, and frustration have been associated with exacerbated tics, with PSP contributing to these feelings.

Modulation of autonomic activity in neurological conditions: Epilepsy and Tourette Syndrome

This manuscript considers the central but neglected role of the autonomic nervous system in the expression and control of seizures in epilepsy (small) and tics in Tourette Syndrome (TS). In epilepsy, consideration of autonomic involvement is typically confined to differential diagnoses (e.g., syncope), or in relation to Sudden Unexpected Death in Epilepsy (SUDEP). Investigation is more limited in Tourette Syndrome. The role of the autonomic nervous system in the generation and prevention of epileptic seizures is largely overlooked. Emotional stimuli such as anxiety and stress are potent causes of seizures and tic activity in epilepsy and TS, respectively. This manuscript will describe a possible neural mechanism by which afferent autonomic projections linked to cognition and behavior influence central thalamo-cortical regulation, which appears to be an important means for controlling both seizure and tic activity. It also summarizes the link between the integrity of the default mode network and autonomic regulation in patients with epilepsy as well as the link between impaired motor control and autonomic regulation in patients with TS. Two neurological conditions; epilepsy and TS were chosen, as seizures and tics represent parameters that can be easily measured to investigate influences of autonomic functions. The EDA biofeedback approach is anticipated to gain a strong position within the next generation of treatment for epilepsy, as a non-invasive technique with minimal side effects. This approach also takes advantage of the current practical opportunity to utilize growing digital health technology.

The role of the autonomic nervous system in Tourette Syndrome

Tourette Syndrome (TS) is a neurodevelopmental disorder, consisting of multiple involuntary movements (motor tics) and one or more vocal (phonic) tics. It affects up to one percent of children worldwide, of whom about one third continue to experience symptoms into adulthood. The central neural mechanisms of tic generation are not clearly understood, however recent neuroimaging investigations suggest impaired cortico-striato-thalamo-cortical activity during motor control. In the current manuscript, we will tackle the relatively under-investigated role of the peripheral autonomic nervous system, and its central influences, on tic activity. There is emerging evidence that both sympathetic and parasympathetic nervous activity influences tic expression. Pharmacological treatments which act on sympathetic tone are often helpful: for example, Clonidine (an alpha-2 adrenoreceptor agonist) is often used as first choice medication for treating TS in children due to its good tolerability profile and potential usefulness for co-morbid attention-deficit and hyperactivity disorder. Clonidine suppresses sympathetic activity, reducing the triggering of motor tics. A general elevation of sympathetic tone is reported in patients with TS compared to healthy people, however this observation may reflect transient responses coupled to tic activity. Thus, the presence of autonomic impairments in patients with TS remains unclear. Effect of autonomic afferent input to cortico-striato-thalamo-cortical circuit will be discussed schematically. We additionally review how TS is affected by modulation of central autonomic control through biofeedback and Vagus Nerve Stimulation (VNS). Biofeedback training can enable a patient to gain voluntary control over covert physiological responses by making these responses explicit. Electrodermal biofeedback training to elicit a reduction in sympathetic tone has a demonstrated association with reduced tic frequency. VNS, achieved through an implanted device that gives pulsatile electrical stimulation to the vagus nerve, directly modulates afferent interoceptive signals. The potential efficacy of biofeedback/VNS in TS and the implications for understanding the underlying neural mechanisms of tics will be discussed.

Autonomic regulation during rest and mental load in Gilles de la Tourette syndrome

Cardiovascular and catecholaminergic activity during mental load were studied in patients with Tourette syndrome. Patients and controls performed the Color Word Test, preceded by a baseline period, with continuous measurements of heart rate and blood pressure. Blood samples for assay of plasma catecholamine concentrations were obtained before and during the test. The patients showed higher heart rate and blood pressure during baseline than controls, but no differences regarding plasma catecholamines. The tics corresponded with transient increases in heart rate and blood pressure. Spectral analysis of cardiovascular variability during mental load gave only limited evidence of increased sympathetic activity and no alterations in parasympathetic activity in the patients. Therefore, our findings indicate enhanced cardiovascular activity in the patients but not during mental load. The effects of tics on the cardiovascular parameters illustrate the functional complexity of the autonomic nervous system in Tourette syndrome.