Tourette's syndrome: clinical and neurochemical correlates

The Pathophysiology of Tics; An Evolving Story

Background:

Tics, defined as quick, rapid, sudden, recurrent, non-rhythmic motor movements or vocalizations are required components of Tourette Syndrome (TS) - a complex disorder characterized by the presence of fluctuating, chronic motor and vocal tics, and the presence of co-existing neuropsychological problems. Despite many advances, the underlying pathophysiology of tics/TS remains unknown.

Objective:

To address a variety of controversies surrounding the pathophysiology of TS. More specifically: 1) the configuration of circuits likely involved; 2) the role of inhibitory influences on motor control; 3) the classification of tics as either goal-directed or habitual behaviors; 4) the potential anatomical site of origin, e.g. cortex, striatum, thalamus, cerebellum, or other(s); and 5) the role of specific neurotransmitters (dopamine, glutamate, GABA, and others) as possible mechanisms (Abstract figure).

Methods:

Existing evidence from current clinical, basic science, and animal model studies are reviewed to provide: 1) an expanded understanding of individual components and the complex integration of the Cortico-Basal Ganglia-Thalamo-Cortical (CBGTC) circuit - the pathway involved with motor control; and 2) scientific data directly addressing each of the aforementioned controversies regarding pathways, inhibition, classification, anatomy, and neurotransmitters.

Conclusion:

Until a definitive pathophysiological mechanism is identified, one functional approach is to consider that a disruption anywhere within CBGTC circuitry, or a brain region inputting to the motor circuit, can lead to an aberrant message arriving at the primary motor cortex and enabling a tic. Pharmacologic modulation may be therapeutically beneficial, even though it might not be directed toward the primary abnormality.

Merging the Pathophysiology and Pharmacotherapy of Tics

Background

Anatomically, cortical-basal ganglia-thalamo-cortical (CBGTC) circuits have an essential role in the expression of tics. At the biochemical level, the proper conveyance of messages through these circuits requires several functionally integrated neurotransmitter systems. In this manuscript, evidence supporting proposed pathophysiological abnormalities, both anatomical and chemical is reviewed. In addition, the results of standard and emerging tic-suppressing therapies affecting nine separate neurotransmitter systems are discussed. The goal of this review is to integrate our current understanding of the pathophysiology of Tourette syndrome (TS) with present and proposed pharmacotherapies for tic suppression.

Methods

For this manuscript, literature searches were conducted for both current basic science and clinical information in PubMed, Google-Scholar, and other scholarly journals to September 2018.

Results

The precise primary site of abnormality for tics remains undetermined. Although many pathophysiologic hypotheses favor a specific abnormality of the cortex, striatum, or globus pallidus, others recognize essential influences from regions such as the thalamus, cerebellum, brainstem, and ventral striatum. Some prefer an alteration within direct and indirect pathways, whereas others believe this fails to recognize the multiple interactions within and between CBGTC circuits. Although research and clinical evidence supports involvement of the dopaminergic system, additional data emphasizes the potential roles for several other neurotransmitter systems.

Discussion

A greater understanding of the primary neurochemical defect in TS would be extremely valuable for the development of new tic-suppressing therapies. Nevertheless, recognizing the varied and complex interactions that exist in a multi-neurotransmitter system, successful therapy may not require direct targeting of the primary abnormality.

Psychopathology in boys with Tourette syndrome: Effects of age on the relationship between psychological and physical symptoms

Tourette syndrome (TS), a neuropsychiatric disorder that presents in childhood and is characterized by recurrent tics, is often associated with a variety of psychological problems. Most studies of concomitant problems have focused on psychiatric comorbidity, with less attention paid to nonsyndrome-specific or subsyndromal emotional and behavioral difficulties. Moreover, little is known about the factors that influence the specificity or severity of psychological problems. We hypothesized that level and type of psychological problem would be influenced by both severity of illness and developmental period. Children with severe tics were predicted to show increased levels of externalizing (undercontrolled) behavior, whereas adolescents with severe tics were predicted to show increased levels of internalizing (overcontrolled) behavior. Forty-one boys with TS were rated by their parents for tic severity (simple and complex motor tics) and psychological symptoms (Connors Parent Symptom Questionnaire and the Child Behavior Checklist). Results partially confirmed the hypothesis, indicating that greater illness severity was associated with greater psychological disturbance, but only in the younger subjects. Among the adolescents, even those with mild tics demonstrated relatively high levels of psychological symptoms. However, there was no indication that developmental period was related to the specific type of problem manifested. Regardless of age, patients with severe tics domonstrated high levels of externalizing behavior, and relatively high levels of internalizing behavior were also seen. Results are discussed in terms of the developmental factors that might influence the relationship between psychological and physical symptoms in children with TS.

Obsessive-compulsive spectrum conditions in obsessive-compulsive disorder and other anxiety disorders

In light of current interest in an obsessive-compulsive spectrum of disorders, this study sought to determine whether comorbidity patterns support the unique relationship hypothesized between these conditions and obsessive-compulsive disorder (OCD). Comparisons were made of lifetime rates of several proposed spectrum conditions in individuals with one of three anxiety disorder principal diagnoses (OCD, social phobia, or panic disorder [PD], N=277). Spectrum conditions examined included tic-related disorders, trichotillomania, skin picking, and eating disorders, with analyses performed on rates both of clinical disorder alone, and clinical and subclinical manifestations jointly. The OCD group was found to differ from both other groups in showing 1) a greater proportion of individuals affected with any lifetime spectrum condition, 2) a greater number of lifetime spectrum conditions affecting each individual, and 3) a greater proportion of individuals having a lifetime history of multiple spectrum conditions. Analyses for specific spectrum conditions indicated differences among the anxiety disorder groups for all spectrum categories except eating disorders, though only in the case of tic-related conditions did OCD differ significantly from both comparison groups. For the other conditions, dissimilar patterns of differences were observed among the three groups, particularly when subclinical manifestations were included. These findings have conceptual and clinical implications, including 1) the salience of tic-related disorders in the OC spectrum, 2) the possibility that the relationship between spectrum conditions and anxiety disorders may take several different forms, and 3) the need for refinement of the hypothesized spectrum.

Informativeness of structured diagnostic interviews in the identification of Tourette's disorder in referred youth

Although specialized programs have greatly advanced the treatment of youth with Tourette's disorder (TD), not all children with TD reach such programs, raising questions as to whether TD is adequately identified outside specialized settings. There is thus a need for evidence that cases identified in the nonspecialty setting are "true cases." Because structured diagnostic interview methodology can reduce errors of omission, this approach can facilitate the identification of TD in referred youth outside specialized programs. Similarities between cases ascertained in specialty and nonspecialty settings would suggest that those identified in the nonspecialty setting were indeed "true cases." Comparisons were made between youth with TD ascertained through a specialized TD program who had both a structured diagnostic interview-derived diagnosis of TD plus an expert evaluation of TD (N = 103), with youth ascertained through a non-TD specialized pediatric psychopharmacology program who had a structured diagnostic interview-derived diagnosis of TD (N = 92). Irrespective of ascertainment source, children with structured interview-derived diagnosis of TD shared similar correlates in terms of tic severity, mean age of onset and duration of tics, as well as patterns of comorbidity well known to be associated with TD in clinical samples. Children meeting diagnostic criteria for TD on structured diagnostic interviews share similarities and patterns of clinical correlates, irrespective of ascertainment through a specialized TD or non-TD specialized clinic. These findings support the usefulness of structured diagnostic interview methodology as a diagnostic aid for the identification of TD in non-TD specialized settings and facilitate delineation of patterns of comorbidity.

Anxiety disorders and tic severity in juveniles with Tourette's disorder

OBJECTIVE

It was hypothesized that comorbidity with anxiety disorders would predict tic severity in youths with Tourette's disorder (TD).

METHOD

Subjects were 190 youths meeting DSM-III-R diagnostic criteria for TD who were consecutively referred to a pediatric psychopharmacology program between 1994 and 1997. Subjects were initially evaluated with a clinical interview and the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Epidemiologic version. Statistical analysis used t tests, chi 2 tests, and logistic regression analysis.

RESULTS

One hundred thirty-four subjects were classified as mild/moderate and 56 as severe TD cases. No meaningful differences were found in socioeconomic status, gender distribution, or age at onset of TD between the 2 groups. The 2 groups could not be differentiated by the presence of comorbid mood or disruptive behavior disorders including attention-deficit hyperactivity disorder. Although obsessive-compulsive disorder (OCD) was overrepresented among the severe TD cases, the difference failed to reach statistical significance. Excluding social and simple phobias, all other anxiety disorders were more clearly overrepresented among subjects with severe TD; separation anxiety disorder most robustly predicted tic severity, irrespective of the presence of OCD or other anxiety disorders.

CONCLUSION

Findings suggest that non-OCD anxiety disorders in general and separation anxiety disorder in particular may be significantly associated with tic severity in referred TD patients.

Anxiolytics, adrenergic agents, and naltrexone

OBJECTIVE

To review extant data on the efficacy and safety of anxiolytic medications (benzodiazepines, buspirone, and other serotonin 1A agonists), adrenergic agents (beta-blockers and alpha 2-adrenergic agonists clonidine and guanfacine), and the opiate antagonist naltrexone that have been used to treat various psychopathologies in children and adolescents. To identify critical gaps in our current knowledge about these agents and needs for further research.

METHOD

All available controlled trials of these medications in children and adolescents published in English through 1997 were reviewed. In addition, selected uncontrolled studies are included.

RESULTS

The major finding, that there are virtually no controlled data that support the efficacy of most of these drugs for the treatment of psychiatric disorders in children and adolescents, is both surprising and unfortunate. For some drugs, e.g., buspirone and guanfacine, this is because no controlled studies have been carried out in children and/or adolescents. For other drugs, e.g., clonidine and naltrexone, most of the placebo-controlled studies have failed to demonstrate efficacy.

CONCLUSIONS

The strongest recommendations for controlled studies of safety and efficacy in children and adolescents can be given for the following drugs: benzodiazepines for acute anxiety; buspirone (and newer serotonin 1A agonists as they become available) for anxiety and depression; beta-blockers for aggressive dyscontrol; guanfacine for attention-deficit/hyperactivity disorder; and naltrexone for hyperactivity, inattention, and aggression in autistic disorder.

Psychophysiological aspects of Tourette's syndrome

Tourette's syndrome (TS), once considered a rare disorder, has been investigated extensively in the last two decades. It is inherited, usually beginning in childhood, and waxes and wanes, usually decreasing in frequency and severity in adolescence and early adulthood. Pharmacotherapy is the usual treatment approach, reducing frequency and severity of symptoms, but it is not a cure and often has side effects. Psychological help for people with TS and their families may be needed for this complex disorder.

Neurobiology of Tourette syndrome

This article includes a discussion of approaches designed to determine neuroanatomic localization through the use of physical examination, electrophysiologic and neuroradiographic studies, and neuropathologic evaluations. The author reviews the anatomy, function, and biochemistry of frontal-subcortical circuits. Inferred and direct evidence that supports a disorder of frontal-subcortical circuits in Tourette syndrome is presented. Studies investigating specific neurotransmitters are reviewed.

The audiogenic startle reflex in Tourette's syndrome

The motor response pattern of the audiogenic startle reflex was studied in 15 Tourette's syndrome (TS) patients and 15 normal, age-matched control subjects, using auditory stimuli at 88 and 114 dB. The louder stimuli readily elicited responses in the orbicularis oculi (in all subjects), masseter, sternomastoid, trapezius, deltoid, and biceps (in most subjects) muscles, with a few subjects having responses in the forearm flexors and quadriceps. The TS subjects did not differ from controls in the onset latency, amplitude, and first peak latency of the reflex response in any of the muscles. Rates of habituation in the orbicularis oculi muscle were widely variable across the subjects, and the two groups did not differ overall in the habituation rates. Our study does not support the reports of an abnormal audiogenic startle reflex in TS.

Tics status

OBJECTIVES

To describe two patients with tics status, propose a definition of this syndrome and draw attention to its clinical significance.

METHOD

Two patients suffering from Tourette's Syndrome who had developed episodes of continual motor tics that lasted from minutes to hours, were non-suppressible and intruded into normal functioning, were treated with an increase in the dose of haloperidol, in one case with the addition of clonazepam.

RESULTS

The offset of the episodes was gradual and the tic disorder was worse after the episodes. One patient had further spontaneous episodes of tics status.

CONCLUSIONS

The recognition of tics status has implications for the management as well as our understanding of the pathobiology of tics and Tourette's Syndrome. The definition of tics status should be standardised.

Tourette syndrome: associated symptoms and most disabling features

Four hundred forty-six patients with Tourette Syndrome (TS) and/or their parents completed a 52-item self-report survey about vocal and motor tics, and the frequency of associated co-morbid conditions of aggression, obsessions and compulsions, attentional problems, sleep disturbance, mood disturbance, anxiety, and self-mutilative behaviours which have been frequently reported in the literature on TS. Respondents also responded to an open-ended question regarding the most disabling aspects of TS. Results were analyzed within two age groups; under 18 years of age (N = 245) and 18 years of age or older (N = 177). Tics and associated conditions were the most frequently reported disabling aspect by both age groups. Subjects under age 18, however, reported significantly more frequent problems with hyperactivity, temper control, aggressive behaviours and sleepwalking than adults with TS.

Obsessive-compulsive disorders in the pediatric dermatology practice

Childhood and adolescent obsessive-compulsive disorders are sometimes seen in dermatology practice. When present, OCD is most frequently manifested in younger patients as trichotillomania, onychotillomania, onychophagia, and acne excoriée. In addition to these disorders, obsessive hand washing, AIDS phobia, and other psychosomatic dermatoses characterized by obsessive-compulsive tendencies are seen in all age groups. It is important to define the nature of any underlying psychiatric disorder before beginning drug treatment of these patients. With the availability of new medications, most notably, clomipramine and fluoxetine, there is reason for optimism regarding the treatment of OCD. Whenever feasible, the dermatologist should not hesitate to involve a psychiatrist to help with diagnosis and treatment when the diagnosis of OCD is being considered.

Prolactin in childhood obsessive-compulsive disorder: clinical correlates and response to clomipramine

Basal prolactin concentrations were measured before treatment in 18 children and adolescents with obsessive-compulsive disorder as well as in 15 of these patients after 4 and 8 weeks of clomipramine treatment. Basal prolactin levels were influenced by a history of chronic tic disorder and by the duration and severity of obsessive-compulsive symptoms. Clomipramine administration significantly increased basal prolactin levels. A slight decline in prolactin levels during the last 4 weeks of clomipramine treatment was positively correlated with a favorable treatment response and negatively correlated with duration of illness. If the changes in prolactin levels observed during clomipramine treatment are due primarily to changes in serotonergic neurotransmission, these data suggest that clomipramine treatment of obsessive-compulsive disorder produces an adaptive decrease in the responsiveness of serotonergic receptors.

Tourette syndrome attributed to frontal lobe dysfunction: numerous etiologies involved

The etiology of Tourette Syndrome (TS) according to prevailing views is unknown; there is evidence for both familial and sporadic cases. The author theorizes that abnormal discharges in the frontal lobes comprise the "final common dysfunction" that results in numerous phenomena labelled Tourette syndrome. Facial, vocal, and other motor symptoms of TS are catalogued in parallel with facial, vocal, and body movements that occur during frontal lobe seizures. The variety of etiologies that cause frontal lobe seizures--when applied to TS--can account more readily for heterogeneity of clinical presentations, the numerous "dual diagnosis" cases, and differential response to medication than can a single-gene theory.