Tourette’s and comorbid syndromes

Abstract

Tourette’s syndrome (TS), a neuropsychiatric movement disorder that manifests itself in childhood, is often associated with comorbid symptomatology, such as obsessions, compulsions, hyperactivity, distractibility, and impulsivity. Epidemiological studies suggest that a substantial number of TS patients develop clinical levels of obsessive-compulsive disorder (OCD) and/or attention deficit hyperactivity disorder (ADHD). This review aims to provide an integrated account of the three disorders in terms of their comorbidity. Neuroimaging studies suggest that all three disorders involve neuropathology of the basal-ganglia thalamocortical (BGTC) pathways: TS in the sensorimotor and limbic BGTC circuits; OCD in the prefrontal and limbic BGTC pathways; and ADHD in the sensorimotor, orbitofrontal, and limbic BGTC circuits. The pattern of comorbidity and other evidence indicates that the TS gene(s) may be responsible for a spectrum of disorders, including OCD and ADHD, but also that the disorders OCD and ADHD can exist in their own right with their own etiologies.

Introduction

TOURETTE’S SYNDROME (TS) is a disorder of childhood onset characterized by simple and/or complex motor and vocal tics. Tics are usually defined as repetitive, stereotyped movements or vocalizations that are “involuntary” (Singer & Walkup, 1991), although more recent clinical observation suggests that some of the repetitive behaviors in TS are voluntary in nature (Miguel et al., 1997). At onset, which is predominantly before 10 years of age, the TS patient typically exhibits one or two simple motor tics, such as eye blinking or neck movements. These symptoms progress over time and usually become more severe and complex (Bornstein, King, & Carroll, 1983). More complex tics include touching objects, squatting, twirling while walking, retracing steps, and hopping. Vocalizations include inarticulate sounds, such as barking, coughing, and grunting, as well as the more complex palilalia (repetition of one’s own words/phrases), echolalia (the repetition of another’s words or phrases), and coprolalia (uttering of obscenities).

A diagnosis of TS occurs in approximately 1 in 1,500 children (Cohen, Riddle, & Leckman, 1992). Familial studies suggest that TS is an autosomal dominant disorder with incomplete penetrance and variable expressivity affecting males 3 times more commonly than females. The latter are more likely to exhibit obsessive-compulsive (OC) behaviors, with or without tics (Eapen, Pauls, & Robertson, 1993). Behaviors such as hyperactivity, impulsivity, and distractibility are also commonly associated with TS (American Psychiatric Association, 1994), which has led to speculations regarding possible genetic links between TS and ADHD.

Obsessive-Compulsive Disorder (OCD) is characterized by the presence of obsessions and/or compulsions that the patient perceives to be excessive at some time during the disorder. Prevalence of OCD in the general population has been estimated at around 1 to 2%, according to epidemiological studies Rasmussen & Eisen 1994, Whitaker et al. 1990, and this may be an underestimation due to a general reluctance for patients to admit to obsessions and compulsions during general screening techniques (Rasmussen & Eisen, 1992). OCD may occur in childhood, however, it more commonly begins to manifest in late adolescence or early adulthood Angst 1994, Leonard et al. 1992.

Obsessions are defined as recurrent and persistent thoughts, impulses, or images that are perceived as intrusive and inappropriate, and that may cause anxiety (American Psychiatric Association, 1994). Common obsessive thoughts include fears of harm/injury to self or loved ones and fears of contamination by dirt or germs Leonard et al. 1992, Singer & Walkup 1991. Compulsions are repetitive and seemingly purposeful behaviors that are usually, but not always, performed in response to an obsession, in a stereotyped fashion or in accordance with certain rules Flament 1994, Rapoport et al. 1995. Typical compulsions include excessive cleaning (e.g., repeated handwashing, showering), checking rituals, reordering or arranging habits, repeating rituals, and counting Leonard et al. 1992, Singer & Walkup 1991. The OCD patient often feels driven to perform these behaviors to neutralize distress associated with the obsessions or prevent a certain stressful situation.

Attention deficit hyperactivity disorder (ADHD) is a complex syndrome whose etiology remains largely unknown. Its primary symptoms include impulsivity, distractibility, and hyperactivity, with additional symptoms including emotional lability and short attention span (Ratey, Middledorp-Crispijn, & Leveroni, 1995). Increasing evidence suggests that problems of failing to inhibit impulsive actions and difficulty in focusing and sustaining attention may be due to a disturbance in frontal lobe function Castellanos et al. 1996, Heilman et al. 1991, Lou et al. 1989, Zametkin et al. 1990, and the most recent theories of ADHD have been developed with this in mind (Barkley, 1997). Frontal lobe involvement is supported by clinical observations of executive-function deficits, such as increased spontaneity, the inability to operate in favor of a remote or abstract reward, a decreased capacity to self-monitor behavior, a decreased ability to respond to stimuli or follow commands, and difficulty maintaining sustained attention Gualtieri 1995, Ratey et al. 1995. For a diagnosis of ADHD, the onset of the disorder is usually before the age of 7 years, though between 30 and 60% of child ADHD sufferers continue to exhibit clinical symptoms in adulthood (Ratey et al., 1995).