Repetitive behaviors are the hallmark of many neuropsychiatric disorders, including Tourette syndrome (TS), obsessive-compulsive disorder (OCD), and autism spectrum disorder (ASD). Tics, compulsions, and stereotypies may appear similar and can be difficult to disentangle. This review addresses similarities and differences between these behaviors including clinical presentations, neuroimaging, genetics, and treatment paradigms in order to clarify the relationship between these disorders. The extensive genetic and neurocircuitry-based similarities raise the possibility that in some cases TS and OCD may represent a single neuropsychiatric entity, such as Tourettic OCD, that lies along the impulsive-compulsive spectrum.
Key points
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Many neuropsychiatric disorders can present with repetitive behaviors that may appear similar, or occur concurrently, and can be difficult to disentangle. Classic examples include complex tics of Tourette syndrome (TS), compulsions of obsessive-compulsive disorder (OCD), and repetitive behaviors of autism spectrum disorder (ASD).
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A distinguishing feature of each disorder is that tics are driven by internal physical urges (premonitory urges), compulsions are driven by internal anxious distress (obsessions), and stereotypies are driven by sensory hyper-arousal or hypo-arousal and a desire to self soothe.
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The genetics of TS, OCD, and ASD may overlap though TS and OCD are more closely genetically related than either is to ASD.
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TS and OCD arise primarily from functional aberrations in the neurocircuitry of the cortico-striato-thalamo-cortical loop during childhood, while ASD presents with a variety of changes including morphometric anatomic changes detectable in the brain as early as infancy.
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The extensive similarity between TS, OCD, and Tourettic OCD may represent an overlapping neuropsychiatric entity that lies along the compulsive-impulsive spectrum.
Introduction
Repetitive behaviors are a hallmark of several neuropsychiatric disorders, most notably Tourette syndrome (TS) and persistent tic disorders, obsessive-compulsive disorder (OCD), and autism spectrum disorder (ASD). These behaviors take different but reminiscent forms: tics in TS, compulsions in OCD, and certain types of restricted and repetitive behaviors (RRBs), such as stereotypies that are one of the hallmarks of ASD. Similarities between compulsions, complex tics, and RRBs can pose a challenge to diagnosis and treatment. The purpose of this review is to evaluate the nature of these repetitive behaviors including their precipitating factors, underlying genetics, neuroimaging, and treatments. Understanding the ways in which these behaviors are alike or differ sheds light on our understanding of shared neuropsychiatric pathophysiology.
Subtypes of repetitive behaviors
Complex Tics
Tics are recurrent, nonrhythmic movements or vocalizations that are driven by a feeling of mounting inner tension or discomfort known as a “premonitory urge.” Tics are categorized as either motor (eye blinking, grimacing, etc.) or vocal (sniffling, throat clearing, etc.). Tics are further subcategorized as either simple or complex. Simple motor tics are involuntary, sudden, meaningless movements such as eye blinking, squinting, or shoulder shrugs. Complex motor tics typically are slower, longer, and may manifest as several behaviors in a row that appear purpose driven and intentional. These include more than one body area and can be combined with a vocalization. Examples of simple vocal or phonic tics are throat clearing, sniffing, grunting, and complex vocalizations include saying specific words, syllables, echolalia, palilalia, or coprolalia. Patients with TS experience motor and vocal tics for at least 12 months with the onset occurring prior to age 18. They typically develop in children ages 6 to 9 years, tend to be most intense between ages 10 to 12, and in 50% to 60% of cases subside in the adolescent years.
Compulsions Versus Complex Tics
OCD is characterized by the presence of obsessions, which are recurrent, intrusive thoughts, images or impulses that evoke fear or anxiety, and lead patients to engage in compulsions: repetitive behaviors performed voluntarily to alleviate the distress elicited by obsessions. Classic examples include obsessive fears of germs that lead to compulsive washing behaviors or obsessive fears of danger that lead to compulsive checking. The typical age of onset is in the prepubertal years and early adolescence.
Compulsions are rarely confused with simple tics which are involuntary. More commonly, compulsions are confused with complex tics, as the sequence of behaviors may appear similar and both serve to alleviate a preceding discomfort. The key distinction is in the nature of this preceding discomfort—compulsions are preceded by anxious thoughts which constitute emotional discomfort, while tics are preceded by a premonitory urge which is most commonly a form of physical discomfort. Premonitory urges are anatomically localized to the region associated with the tic and precede the tics by a few seconds. These behaviors are further distinguished by their terminal goals; compulsions abate when anxiety is alleviated, while complex tics abate when the premonitory urge is quenched. Individuals with compulsions typically are more aware of their actions than those with tics, or patients with ASD who have motor stereotypies.
Tourettic obsessive-compulsive disorder: compulsive complex tics?
The term Tourettic OCD (TOCD) describes patients who present with both tics and compulsions that are closely intertwined. These patients’ movements initiate as involuntary tics driven by a premonitory urge, though a patient will continue to engage in the tic volitionally and compulsively until the tic has been performed “just right.” The “just so” phenomenon combines features of a premonitory urge and anxiety that the tic must be performed in a precise way. The distinction between TOCD and OCD lies in the nature of the anxiety: for TOCD, the anxiety is secondary to the premonitory urge and the need to alleviate physical discomfort and does not arise from intrusive emotional fears such as related to germs or danger. Thus, TOCD behaviors lie at the interface of tics and compulsions and have been described as “compulsions without obsessions” or “cognitive tics.”
TOCD is seen typically in patients ages 7 to 13. Patients with TOCD have a tendency toward behaviors such as tapping, rubbing a specific way, or vocal tics, any of which may be more complex and specific than tics seen in TS. The actions tend to involve multiple body parts or multistep progression of movements. Vocalizations tend to be longer and more complex.
Compulsions and Complex Tics Versus Restricted and Repetitive Behaviors of Autism Spectrum Disorder
ASD is a neurodevelopmental disorder present (or at least potentiated) from birth. To meet the Diagnostic and Statistical Manual of Mental disorders, 5th edition (DSM-5) diagnostic criteria for ASD, an individual must present with deficits in 3 areas of verbal and nonverbal social interaction and at least 2 out of 4 types of RRBs. The 4 subtypes can be grouped into 2 distinct categories.
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Repetitive sensorimotor behaviors that include:
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Stereotyped motor movements such as hand flapping, rocking, self-injury such as skin picking, or repetitive manipulation of objects.
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Hyper-reactivity or hypo-reactivity to sensory input such as pain/temperature/sounds/textures, or visual fascination with object, such as lights or spinning fans or discs.
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Insistence on sameness behaviors that include:
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Inflexibility around well-established routines, such as difficulty with transitions, or strict adherence to sleep/food/clothing preferences.
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Highly restricted fixated interests that are abnormal in intensity or focus.
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The average age of diagnosis is around age 2 to 4 years unlike OCD, TS, and TOCD which typically arise during latency and early adolescence. In further contrast, the stereotypies of ASD are associated with sensory under-arousal or over-arousal. Patients are often overstimulated by social stimuli, such as noises, crowds, lights, or strong emotions including anger, joy, excitement, and in contrast are understimulated by nonsocial stimuli including periods of solitude or boredom. In both hyperaroused and hypoaroused states, RRBs, known as “stimming” behaviors, provide sensory feedback that is believed to be self-soothing. In contrast to OCD and TS which are preceded by internal discomfort, RRBs can be precipitated by external sensory input that is either overstimulating or understimulating. Furthermore, these behaviors differ in their terminal goals: ASD behaviors such as rocking, hand wringing, spinning, repeating scripted words, or noises tend to be continuous and nongoal directed, whereas the compulsions of OCD are goal oriented toward alleviating a specific intrusive thought: for example, repeated washing or cleaning to alleviate fears of contamination, and complex tics may vary to alleviate a particular premonitory urge within a specific body region. Patients with OCD, TS, and TOCD feel compelled to perform behaviors due to anxiety or distress, whereas patients with ASD typically find these behaviors calming ( Table 1 ).
| Patient | Clinical Presentation | Diagnoses | Treatment |
|---|---|---|---|
| J.B. 15-year-old male | J.B. was diagnosed with TS at age 9. His tics over the years included eye blinking, facial movements, grunting noises, and vocalizations. They can be suppressed in certain situations and are worse at home. At age 13, he developed germophobia and handwashing compulsions as well as needing to use separate utensils for different foods. In addition, he cannot touch door knobs or handles and struggles to get into a car without touching the door handle. He is highly anxious about “contamination” to the point of difficulty bathing or toileting himself due to fear of contamination. | OCD (germophobia) comorbid with: TS Generalized anxiety disorder ADHD Specific learning disability | Multiple past selective serotonin reuptake inhibitor trials. Currently doing well on fluvoxamine, guanfacine, and exposure and response prevention therapy |
| R.S. 13-year-old male | R.S. developed tics at age 7 which have escalated to include facial grimaces, complex sequences of head movement followed by arm flailing, throat clearing and vocalizations, and echolalia. Obsessive-compulsive tendencies started around age 10 and included a strong urge to perform things symmetrically. He also has intrusive thoughts about doing his tics in sequences of nine. His tics are preceded by a premonitory urge, but he may need to repeat a tic an extra number of times to get to a multiple of 9 or to perform it “Just right.” | TS (initially), Tourettic OCD (later) comorbid with: Oppositional-defiant syndrome Sensory processing disorder ADHD Generalized anxiety disorder | Tics continue to be problematic but overall have improved on a combination of aripiprazole and sertraline. He has tried comprehensive behavioral intervention for tics and cognitive behavioral therapy. |
| B.D. 18-year-old male | B.D. has a long-standing diagnosis of autism spectrum disorder and moderate intellectual disability in the context of a partial duplication of chromosome 7P. Since age 18 mo he has had repetitive hand flapping and full body rocking. For years B.D. has been skin picking to the point that he has had scabs from bleeding. During puberty he developed eye blinking which has resolved, but continues to have hand flapping with one or two arms when overwhelmed or excited. He also struggles to make and maintain friendships and parents report that interactions feel rote and transactional. | ASD comorbid with: Intellectual disability Anxiety, unspecified Body-focused repetitive disorder OCD TS | Doing really well on fluoxetine, applied behavioral analysis therapy, very structured school and home supports with consistent routines, visual aids, and social skills training |
The RRBs of ASD include restricted interests and insistence on sameness that are distinct from the repetitive motor behaviors. Restricted interests present as perseverance on topics such as numbers, facts, trains, planes, maps, or weather patterns and are distinguished by intensity beyond that of neurotypical peers. Restricted interests are sparked by interest in the topic, in contrast to OCD obsessions or Tourettic premonitory urges which are distressing if not satisfied. Additionally, fixated interests of patients with ASD are independent of their repetitive motor behaviors, whereas the obsessions and premonitory urges of OCD, TS, and TOCD drive the compulsive or tic behaviors.
Neuropsychological testing further highlights distinctions between restricted interests and intrusive thoughts. Patients with ASD demonstrate higher deficits on tasks of cognitive flexibility and set shifting, while patients with OCD demonstrate higher deficits in domains of inhibition and impulse control. Language and cognitive impairments are common in ASD though not typically seen in OCD, TS, or TOCD. Lower nonverbal intelligence quotient (IQ) correlates with higher frequency of repetitive sensory motor RRBs, while higher nonverbal IQ correlates with an increase in restricted interests and insistence on sameness. In contrast, the types of compulsions and complex tics do not correlate with variation in IQ.
Generally, RRBs, compulsions, and complex tics lessen with age. Sixty to eighty percent of patients outgrow TS by adulthood. Intrusive thoughts of OCD and fixated interests of ASD often continue into adulthood though individuals with OCD develop increased insight and may hide their compulsions out of social discomfort. , While patients with ASD may continue to lack social awareness and engage in RRBs openly even as adults, depending on the severity of ASD and response to applied behavioral analysis therapy.
Neuroimaging of Tourette syndrome, obsessive-compulsive disorder, and autism spectrum disorder
The overlapping neurocircuitry of TS and OCD is best characterized within neuropsychiatric disorders and, as we, the authors, have previously discussed a possible neurocircuitry for TOCD. Briefly, TS and OCD symptoms are primarily rooted in an imbalance of excitatory and inhibitory signaling in the cortico-striato-thalamo-cortical (CSTC) circuits. The CSTC can be broken down into 3 subnetworks: a motor circuit involved in habit formation and top-down motor control, an associative circuit involved in controlling goal-directed behaviors, and a limbic circuit involved in motivation and reward. Varying levels of imbalance in these 3 circuits are believed to drive the distinctions between TS, OCD, and TOCD behaviors.
Functional magnetic resonance imaging (FMRI) imaging of both OCD and TS supports the notion that both arise from the dysfunction of overlapping brain regions including the sensorimotor cortex and basal ganglia. Transcranial magnetic stimulation shows increased sensorimotor activity and decreased baseline inhibition in the premotor and supplemental motor cortices in both complex tic disorders and OCD. Patients with both complex tics and OCD (consistent with TOCD) show even greater area of involvement of the prefrontal, caudate, and limbic networks, with less reciprocal inhibition than is seen in the presence of only complex tics or OCD alone.
In contrast, while the neuroimaging of ASD shares some similarities with OCD and TS such as abnormalities in the CSTC, there are also several key distinctions, which have been studied by direct large-scale comparison. , In contrast to TS and OCD which arise primarily from a functional imbalance in signaling during childhood, ASD is marked by changes in brain volume and patterning in infancy. Infants at high risk for ASD demonstrate changes in cortical volume within the first year of life. Changes in cerebellar and subcortical volumes have also been shown by age 4 to 6 months, and this has been linked to repetitive behaviors by age 3. Tics have been associated with cerebellar volume changes though this is less prevalent than in ASD. Areas of the limbic system, including the amygdala, were reported to be significantly larger in children aged 2 to 5 with ASD. These changes in brain volume are associated with the severity of social deficits. Over the lifespan, small but significant reductions have been shown in subcortical volumes of key structures which have not been demonstrated in patients with OCD or TS. Diffusor tension imaging (DTI) imaging shows abnormal fractional anisotropy in 12 of 15 white matter tracts in infants who developed ASD as compared with typically developing infants. Many of the white fiber tracts are those implicated in repetitive behaviors, social communication, (such as joint attention), language acquisition, and cognitive rigidity. This is in contrast to OCD, TS, and TOCD in which functional upregulation or downregulation of circuits in the CSTC is more heavily implicated than morphometric changes.
An additional important finding is that children at risk for ASD demonstrate deficits in left-hemispheric response to speech and abnormal right-lateralized temporal cortex response to language. Failure to develop language comprehension is considered one of the earliest warning signs for ASD and is not present in OCD, TS, or TOCD.
Genetics
Tic disorders, OCD, and ASD do not follow simple Mendelian inheritance and much remains unknown. TS and OCD are among the most heritable childhood-onset neuropsychiatric disorders with familial inheritance as high as 50% to 80%, with cross diagnostic heritability and up to 60% comorbidity by some estimates. Comorbidity of ASD with OCD ranges from 25% to 37%. While there is overlap between all 3 disorders, there is consistently closer genetic association between TS and OCD than either shares with ASD. While similar loci may be implicated in all 3, the genetic architecture may overlap more highly between TS and OCD. For example, OCD and TS are associated typically with duplications at the 16p11.2 locus, while ASD can arise from both duplications and deletions of 16p11.2. , In TS and OCD, most genetic mutations encode proteins in the dopaminergic, serotonergic, and glutamatergic pathways within the shared CSTC neurocircuitry. What distinguishes ASD from TS and OCD in terms of the genetic architecture of autism is that in addition to rare variants found in at least 800 genes, there are many genetic syndromes that have been associated with the symptoms of autism. A large subset of patients with ASD is found to have chromosome deletions or duplications (eg, 15q11.2, BP1-BP2, 16p11.2, and 15q13.3) and specific syndromes such as Down (trisomy 21), Williams (chromosome 7q11.2 deletion), Turner (45,X), Phelan-McDermid (22q13 deletion), Smith-Magenis (17p11.2 deletion), Shprintzen/velocardiofacial (22q11 deletion), or single-gene disorders (eg, tuberous sclerosis [TSC1 and TSC2 genes], neurofibromatosis [NF1 and NF2 genes], X-linked Rett [MECP2 gene], and fragile X [FMR1 gene] syndromes). This is distinct from TS and OCD which are clearly polygenic, and only rare cases can be explained by specific variants in these genes. In fact, though many genes have been implicated in large population genome-wide association studies of TS and OCD, they account for less than 2% of affected individuals. Taken together, genetic data for TS, OCD, TOCD, and 50% of cases of ASD support a role for multiple common variants of small effect size that are thought to be distributed widely across the genome.
OCD and TS have the highest genetic correlation in pairwise testing as well as high heritability when compared with other neuropsychiatric disorders including ASD and attention-deficit/hyperactivity disorder (ADHD). TS shares genetic similarity to both ASD and OCD though is more closely correlated with OCD, while OCD and ASD show less homogeneity. Environmental and epigenetic factors, including in utero exposures are believed to play an important role in heterogeneity of clinical presentation. ,
Treatment
Treatment interventions applied to TS, OCD, TOCD, and RRBs of ASD all involve psychoeducation of the families, behavioral therapy, and sometimes pharmacotherapy. A subset of patients present with more than one psychopathology.
First line treatments for TS and OCD include Comprehensive Behavioral Intervention for Tics (CBIT), Cognitive Behavioral Therapy (CBT), and Exposure Response Prevention Therapy (ERPT) for OCD. When medications are needed, there is some overlap in management of TS and OCD though the order of use varies: selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SSNRIs) are first line for OCD while alpha-adrenergic agonists are first line for tics, with each class being second line for the alternative disorder. Tricyclic antidepressants are equally effective but have a higher side effect profile compared with SSRIs. In both TS and OCD, second-generation antipsychotics, especially aripiprazole and risperidone, may be added for augmentation of refractory cases or for patients who cannot tolerate first line agents. First-generation antipsychotics are less favored due to metabolic and extra-pyramidal side effects.
Patients with TOCD often require combined treatments. No TOCD-specific behavioral therapies have been created through a combination of CBIT, CBT, and ERPT that are often utilized to help patients identify the premonitory urge, redirect the tics into a competing behavior, and tolerate the distress of not being able to complete the tic “just right.” Unfortunately, scarcity of therapists trained in both ERPT and CBIT and the variability in provider quality remain a barrier to access. Medication management is nearly always needed and includes polypharmacy of an SSRI and an alpha-agonist to address both anxious distress and tics. In many cases, antipsychotics are needed for additional augmentation.
The underlying neurobiology of ASD involves structural changes within the central nervous system that are difficult to modulate pharmacologically. First line treatments include behavioral therapy primarily based on applied behavioral analysis and social skills training. Therapy for RRBs is targeted primarily at behaviors that lead to self-injury or are problematic. Treatment of stereotypies and self-injurious behaviors includes response interruption and redirection (interruption of the self-injurious behaviors), response cost procedures (removal of a positive consequence when the problematic behavior occurs), and functional communication training (teaching the individual an appropriate communication response that can be used to obtain the same reinforcer as the problematic behavior). For higher order repetitive behaviors of ASD that include obsessive-compulsive behaviors, ERPT and CBT are employed similarly to the treatment of OCD or TOCD. The therapeutic options for routines and insistence on sameness behaviors may involve differential reinforcement of variability that uses positive reinforcement to model the behaviors. These interventions reduce repetitive behaviors in autism and can decrease aggression.
However, for general stereotypies, or “stimming” behaviors, there has been a shift away from interventions that target their removal as these behaviors are now seen as calming and beneficial to the child. ASD-specific therapies have shifted to focus on positive social-emotional cognition and skills rather than exclusively decreasing stereotypies. This is in sharp contrast to TS, OCD, and TOCD in which reducing the behavior is an essential part of treatment.
When medication is indicated for ASD, second-generation antipsychotics risperidone and aripiprazole are FDA approved for aggression and irritability in ASD. For general stereotypies, SSRIs have been shown to be more effective than antipsychotics and help more with motor stereotypies than vocal ones. However, generally the medications effective for tics are not as effective with stereotypies. Studies have also been limited by the side effect profiles of the medications.
Discussion
Over the past decade improved diagnostic, genetic, and imaging tools have enhanced our understanding of the repetitive behaviors that are a hallmark of TS, OCD, and ASD. However, while TS, OCD, and ASD all share some commonalities, the particular similarity between TS and OCD becomes highlighted when evaluated against other disorders with stereotyped behaviors, such as ASD ( Table 2 ).
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