Obsessions are persistently recurring thoughts, impulses, or images that are experienced as intrusive, inappropriate, and distressing, and that are not simply excessive worries about realistic problems. Compulsions are repetitive behaviours or mental acts that a person feels driven to perform according to a rigidly applied rule, in order to reduce distress or to prevent some dreaded outcome. Obsessions and compulsions are egodystonic, i.e. there are considered by the subject himself as irrational or unrealistic, and are, at least partly, resisted. Children and adolescents with OCD may hide their symptoms, or will only allow them to appear at home, or in the presence of family members, suggesting partial voluntary control.

The clinical presentation of OCD during childhood and adolescence has been documented in various cultures, with clinical series
reported from the U.S., Japan, India, Israel, Denmark, and Spain. Typically, children and adolescents with OCD experience multiple obsessions and compulsions, whose content may change over time. The most frequent obsessions in young people include fear of dirt or germs, of danger to self or a loved one, symmetry or exactness, somatic, religious and sexual obsessions. The most common compulsions consist of washing rituals, repeating, checking, touching, counting, ordering, and hoarding. Generally, compulsions are carried out to dispel anxiety and/or in response to an obsession (e.g. to ward off fear of harm). However, some obsessions and rituals involve an internal sense that ‘it does not feel right’ until the thought or action is completed, and certain children with OCD may be unable to specify the dreaded event that the compulsive rituals are intended to prevent, beyond a vague premonition of something bad happening. Simple compulsions, such as repetitive touching or symmetrical ordering, may even lack any discernable ideational component, and may be phenomenologically indistinguishable from complex tics. Several symptom dimensions have been identified in OCD, which could suggest possible aetiologic heterogeneity. Based on the symptom categories of the Children’s Yale-Brown Obsessive-Compulsive Scale (CY-BOCS, the most widely used symptomatic measure in paediatric OCD research,⁽¹⁾) Stewart et al.⁽²⁾ identified four distinct factors, using principal components analysis: (1) symmetry/ordering/repeating/checking; (2) contamination/cleaning/aggressive/somatic; (3) hoarding; and (4) sexual/religious symptoms. These symptom dimensions are congruent with those described in similar studies of adults with OCD, suggesting fairly consistent covariation of OCD symptoms through the developmental course.

Tics are sudden, rapid, non-rhythmic, stereotyped, repetitive movements (motor tics) or sounds (vocal tics). They may mimic simple or more complicated fragments of normal motor or vocal behaviours, which are misplaced in context. Tics vary greatly in nature, location, number, intensity, forcefulness, and frequency.^{(4, 5)} Common simple motor tics are neck jerking, eye blinking, elevation of shoulders, mouth movements. Common simple vocal tics include throat clearing, sniffing, sucking air, grunting, snorting, humming, or barking. Complex motor tics may combine simple tics, and involve facial movements, jumping, gyrating, touching, kicking, grooming behaviours, or echokinesis (repeating someone else’s movement). They may appear to be purposive in character, as brushing hair back, or suddenly rotating on one foot to make a 360-degree turn. In a small fraction of cases, the complex motor tics are self-injuring behaviours, which may be potentially dangerous. Complex verbal tics include the repetition of what was just heard (echolalia) or said (palilalia), or socially inappropriate utterances (coprolalia), even disguised through sign language. The specific tic repertoire of an individual typically changes over time with no predictable course, but complex tics are rare in the absence of simple tics. Tics often occur in discrete unpredictable bouts over the course of a day, separated by tic-free intervals. The combination of bouts over different time scales explains why globally tics wax and wane over time.

Tics are suggestible, as indicated by their transient reappearance when they are recalled. They are also suppressible, as they can generally be willfully held back for brief periods of time. Tics are preceded by an inner tension, an urge to move or utter that may build-up during suppression. Suppressing tics requires mental effort and may accentuate inattention; conversely, attentional problems decrease the ability to suppress tics, and are associated with more severe tics. Various premonitory sensory urges have been reported to prompt the tics, together with feelings of inner conflicts over whether and when to yield to these urges. Sensory urges include focal tension, pressure, tickling, cold, warmth, paresthesias, and generalized inner tension or anxiety. They usually arise in the part of the body involved in the subsequent motor act, and completing the tic seems to yield a temporary relief of the urge. Also, various auditory and visual cues, highly selective for each individual, can elicit tics, and some patients are extremely sensitive to these external cues, as in echo phenomena. Excitement and fatigue typically worsen tics, which are often more frequent and forceful when the individual is alone. Activities requiring fine motor skills and attention improve tics. Although much diminished, tics can occur during sleep, unlike many other movement disorders.

Children and adolescents with tic disorders may present a broad array of associated behavioural difficulties, including OC symptoms, disinhibited speech or conduct, impulsivity, distractibility, and motor hyperactivity.⁽⁵⁾ The presence of motor and/or phonic tics can be associated with difficulties in self-esteem, self-definition, family life, peer acceptance or relationships, and school performance.

The age at onset of OCD appears bimodal.⁽⁶⁾ Prepubertal onset is associated with a male preponderance and an increased risk for tic disorders, including Tourette’s disorder. A second peak of onset occurs at or after puberty. Overall, the mean age at onset of OCD in children and adolescents have ranged from 9 years in referred subjects⁽⁷⁾ to 12.8 years in a community sample.⁽⁸⁾

The median onset age for simple motor tics is between 4 and 6 years.⁽⁹⁾ Phonic or vocal tics usually appear several years after the onset of motor tics, in most cases between 8 and 15 years. Many young children are completely oblivious of their tics, or experience them as wholly involuntary. Premonitory urges typically show up several years after the onset of the tics, on average around 10 years of age. Suppressibility of tics developmentally precedes awareness of premonitory urges, but may get easier as awareness increases.⁽¹⁰⁾

In community-based samples of adolescents with OCD, there are approximately equal numbers of males and females, while in most studies of referred children and youth with OCD, males outnumber females by 2:1 or 3:1.⁽¹¹⁾

Most studies show that the prevalence of tics is higher among boys than girls, with a ratio of 6-8:1 in clinic-based samples, and about 2:1 in community-based studies.⁽¹²⁾ The sex ratio generally increases with tic duration and severity. Thus, in one study, the ratio of boys to girls was 1.6:1 for motor tics present for 1-2 consecutive months, increasing to 7.5:1 when tics were present for 2 non consecutive months, or more than 3 months.⁽¹³⁾

In referred children and adolescents with OCD, the frequency of a diagnosis of any tic disorder ranges from 17 per cent to 40 per cent, and that of Tourette’s disorder from 11 per cent to 15 per cent.⁽¹⁴⁾
Conversely, one study found that 29 per cent of Tourette’s disorder patients displayed OC behaviours.⁽¹⁵⁾ In longitudinal studies, about 50 per cent of children and adolescents with Tourette’s disorder develop OC symptoms or OCD by adulthood,⁽¹⁶⁾ whereas, in a follow-up study of children and adolescents initially treated for OCD, nearly 60 per cent were found to have a lifetime history of tics that ranged from simple, mild, and transient tics to Tourette’s disorder, for which the rate was 11 per cent.⁽¹⁷⁾ On the basis of personal or family history of tics, a distinction has been proposed between ‘tic-related OCD’ and ‘non-tic-related OCD’, under the assumption that the two forms might differ in terms of clinical phenomenology, neurobiological concomitants, and responsiveness to pharmacological interventions.⁽¹⁸⁾ Tic-related OCD appears to have an earlier onset, and to occur more frequently in boys than in girls. The need to touch or rub, blinking and staring rituals, worries over symmetry and exactness, a sense of incompleteness, and intrusive aggressive thoughts and images, are significantly more common in tic-related OCD, whereas contamination worries and cleaning compulsions are more frequent in patients with non-tic-related OCD.

The overall lifetime psychiatric comorbidity in children and adolescents with OCD is about 75 per cent, both in referred and in community cases. The most common conditions comorbid with OCD are affective disorders, with prevalence ranging across studies from 8 per cent to 73 per cent for mood disorders, and from 13 per cent to 70 per cent for anxiety disorders.⁽¹⁹⁾ While occurring less frequently in non-referred subjects, a high rate of disruptive behaviour disorders—attention deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder—has been reported in subjects seen in paediatric OCD clinics. In girls, OCD can be comorbid to anorexia nervosa.

Less than 10 per cent of clinically referred children and adolescents with Tourette’s disorder do not have another morbid condition. About 55 per cent also have ADHD, and more than a third have anger control problems.⁽⁹⁾ Rage attacks in response to minimal provocation, lasting from a few minutes to an hour and usually followed by remorse, as well as an increased vulnerability for drug abuse, depression, and antisocial behaviour, are primarily observed when comorbid ADHD is present. Globally, comorbidity of Tourette’s disorder increases in adolescence, but more markedly for OCD and anxiety disorders in those without ADHD. Individuals with Tourette’s disorder have consistently shown difficulties with fine motor control and visual motor integration, as well as impairment in procedural or habit-based learning. Sleep is often disturbed, with increased short lasting motor activity, especially in non-REM sleep, compared to healthy controls.

Psychological theories of OCD have encompassed psychoanalytic as well as more general non-psychodynamic etiological approaches, focusing alternatively on volitional, intellectual, and/or emotional impairment. Freud’s famous patient, the Rat Man, has been seen as a paradigm of a psychologically determined illness, illustrating the central role of anal sadistic concerns with control, ambivalence, magical thinking, and the salience of defenses such as reaction formation, intellectualization, isolation, and undoing. Freud also provided fascinating speculations on the similarity between OC phenomena, children’s games, and religious rites. Later, Anna Freud stated that ‘obsessional outcomes are promoted by a constitutional increase in the intensity of the anal-sadistic tendencies probably as the result of inheritance combined with parental handling’. However, despite the beautifully described dynamics of obsessional symptoms, most illustrative of unconscious processes, the psychoanalysts have also pointed out the extreme difficulty in treating OCD with classical analytic treatment.

Even though psychological factors are insufficient to cause Tourette’s disorder, tic behaviours have long been identified as stress-sensitive, and temporally associated with important events in the lives of children. In a prospective study over 2 years, children and adolescents with Tourette’s disorder and/or OCD experienced significantly more psychosocial stressors than did healthy controls, and the level of psychosocial stress was a significant predictor of future tic and OC symptoms severity.⁽²⁹⁾

Although a variety of biological aetiologies have been proposed in OCD since the 19th century, modern neurobiological theories began with the clinical studies showing that clomipramine and other serotonin reuptake inhibitors (SRIs) had a unique efficacy in treating the disorder. This inspired a ‘serotoninergic hypothesis’ of OCD (see Chapter 4.8). In children, the involvement of the serotonin system in the pathophysiology of OCD is supported by one study in which improvement of OC symptoms during clomipramine treatment was closely correlated with pretreatment platelet serotonin concentration,⁽³⁰⁾ and reports of decreased density of the platelet serotonin transporter in children and adolescents with OCD but not in those with Tourette’s disorder.⁽³¹⁾ However, the
delayed and incomplete action of serotonergic drugs, suggesting multiple effects on other neurotransmitters as well, and numerous biochemical studies of OCD patients and controls have not yet indicated a single biochemical abnormality as a primary etiological mechanism in OCD.

In Tourette’s disorder, multiple neurochemical systems have been implicated by pharmacological and metabolic studies, but a primary disturbance in the dopaminergic system is supported by the tic suppressing effect of dopamine receptor antagonists (see below). Post-mortem studies have shown an increase in the number of presynaptic dopamine transporter sites in the striatum and the frontal cortex of individuals with Tourette’s disorder. PET/SPECT studies have demonstrated greater binding to dopamine transporter sites in both the caudate and putamen nuclei,⁽³²⁾ increased dopamine release by psychostimulants in the putamen,⁽³³⁾ and an association between density of dopamine receptors in the caudate and severity of tics.⁽³⁴⁾ The ‘tonic-phasic hypothesis’ proposes both a hyperresponsive spike-dependent (phasic) dopaminergic system (possibly related to an alteration in afferent cortical inputs), and a reduction in tonic dopamine levels (possibly secondary to an overactive dopamine transporter system), that would upregulate pre- and postsynaptic dopamine receptors and further increase the phasic-tonic unbalance. There is also some evidence for the role of serotonin in tic disorders, notably a study showing that reduced serotonin transporter binding correlated with vocal tics and OC symptoms.⁽³⁵⁾

In both OCD and Tourette’s disorder, twin and family studies provide strong evidence that genetic factors are involved in the vertical transmission of vulnerability within families. The average concordance rate in monozygotic twins is 65 per cent for OCD,⁽³⁶⁾ and 53 per cent for Tourette’s disorder.⁽³⁷⁾ Family studies have consistently found higher rates of OCD and tic disorders in probands with paediatric OCD, as well as higher rates of tic disorders and OCD in those with tic disorders. Thus, Lenane et al.⁽³⁸⁾ investigating 147 first-degree relatives of children and adolescents with OCD found that 44 per cent of the families had a positive history of tics in at least one first-, second-, or third-degree relative. Conversely, Pauls et al.⁽³⁹⁾ reported that the prevalence rates of OCD and tic disorders were significantly greater among the first-degree relatives of 100 probands with OCD (10.3 per cent and 4.6 per cent, respectively) than among relatives of psychiatrically unaffected subjects (1.9 per cent and 1.0 per cent). These findings suggested that Tourette’s disorder and some forms of OCD could be variant expressions of the same underlying genetic factors.

Results from two genome-wide scans have been reported,^{(40, 41)} with the strongest linkage peaks being on chromosome 2 for Tourette’s disorder (p=0.00004), and chromosome 3 for OCD (p=0.0002); there were also regions that showed moderate evidence for linkage to both disorders. In early-onset OCD, family-based evidence for association at several serotonin system genes (SCL6A4, HTR1B, HTR2A) and brain-derived neurotropic factor (BDNF) has been reported in some studies, and the association seemed stronger in subjects with tic disorders associated with OCD.⁽⁴²⁾ There is also preliminary evidence for an association between OCD and two glutamate genes, the glutamate transporter gene (SLC1A1), and a glutamate receptor gene (GRIN2B).⁽⁴³⁾ A complementary approach involving examining rare cases of cytogenetic abnormalities co-segregating with Tourette’s and related disorders has pointed to regions on chromosomes 3p, 7q, 8q, 9p, and 18q.⁽⁴⁴⁾

Thus, as suggested by earlier family studies, OCD and Tourette’s disorder might have both shared and distinct susceptibility genes involved in their etiology. It is likely that epigenetic and non genetic factors may also contribute to phenotypal heterogeneity. A range of prenatal and perinatal events have been suggested as risk factors for increased tic severity, including lower birth weight, in utero exposure to caffeine, alcohol or tobacco, and maternal stress.⁽⁴⁵⁾ As the basal ganglia are especially sensitive to hypoxia, it is possible that factors associated with transient hypoxia could increase the risk for Tourette’s disorder in those with a genetic vulnerability.

It has been known for a long time that OC symptoms could be associated with neurological disorders of motor control, including Tourette’s disorder, Huntington’s disease, Parkinson’s disease, as well as traumatic or infectious lesions of the basal ganglia.⁽⁴⁶⁾ Conversely, in both adults and children with typical OCD, an increased frequency of soft neurological signs has been reported.⁽⁴⁷⁾ Since the era of neuroimaging, numerous studies have consistently found that the ventral prefrontal cortical (VPFC) regions, such as orbital prefrontal cortex and anterior cingulate cortex, the striatum, the basal ganglia and the thalamus were basic brain structures involved in the pathophysiology of OCD. These studies have generally identified abnormally high metabolic activity and/or blood flow in the orbital cortex and the head of the striatal caudate nucleus in untreated OCD subjects at rest, compared to various control populations.^(48,49) Furthermore, the same two regions, as well as the thalamus to which each projects, have shown further increase in activity during OC symptom provocation. In several functional neuroimaging studies of patients with childhood onset OCD, measures of VPFC and striatal activity correlated positively with OCD symptom severity and treatment response.^(50,51) Some studies have also indicated that the anatomy of the caudate, putamen and globus pallidus could differ between paediatric OCD patients and controls,⁽⁵²⁾ especially in cases of paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS).⁽⁵³⁾ Although most studies have implicated the VPFC in the pathogenesis of OCD, recent investigation suggests a role for the dorsolateral prefrontal cortex (DLPFC) as well. Thus, one study found a significant increase in N-acetyl-aspartate (NAA), a neuronal marker of activity, in the left DLPFC of unmedicated paediatric OCD patients compared to controls.⁽⁵⁴⁾

Recent MRI studies found that the volume of the caudate nucleus is decreased in both children and adults with Tourette’s disorder, whereas the volume of putamen and globus pallidus nuclei are primarily reduced in adults with the disorder.⁽⁵⁵⁾ This is consistent with a study comparing monozygotic twins discordant for tic expression, in which caudate nuclei volumes were smaller in the more severely affected co-twin.⁽⁵⁶⁾ In addition, subjects with Tourette’s disorder were found to have larger volumes in dorsal prefrontal and parieto-occipital regions.⁽⁵⁷⁾ Although no association was found between tic severity and the volumes of the basal ganglia, ratings of worst-ever tic severity were associated with larger orbito-frontal and parieto-occipital regions. In one recent study, cortical and subcortical hyperintensities that are considered as a subclinical manifestation of small-vessel disease, were significantly more abundant in children and adolescents with Tourette’s
disorder, OCD or ADHD than in healthy controls.⁽⁵⁸⁾ These results support a primary disturbance of the cortico-striato-pallidalthalamo-cortical circuit, especially the projection into or out of the striatum. The small reduction of the caudate (about 5 per cent) may represent a marker for Tourette’s disorder, and larger prefrontal cortex would likely result from the ability to suppress tics. Although tics are highly heritable, non genetic factors appear to contribute to these brain differences.

For the last decade, clinical and research interest has grown in an autoimmune model of OCD and/or tic disorders, which could apply to a subgroup of subjects whose disorder begins abruptly during childhood. An association was first reported between acute onset OCD and Sydenham’s chorea, a childhood movement disorder associated with rheumatic fever, which is thought to result from an antineuronal antibody-mediated response to group A beta-haemolytic streptococcus (GABHS), directed at portions of the basal ganglia.⁽⁵⁹⁾ OCD, or some of its symptoms, have been reported in 70 per cent of Sydenham’s chorea cases.^{(60, 61)} Furthermore, in the absence of the neurological symptoms of Sydenham’s chorea, post-streptococcal cases of childhood-onset OCD, tics and/or other neuropsychiatric syndromes have been described under the acronym of paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). Swedo et al.⁽⁶⁾ defined this novel group of patients using five diagnostic criteria: presence of OCD and/or tic disorder, prepubertal onset, episodic course of symptom severity, abrupt onset or dramatic exacerbations of symptoms temporally associated with GABHS infections (as evidenced by positive throat culture and/or elevated anti-GABHS titers), and association with neurological abnormalities (motoric hyperactivity or adventitious movements, such as choreiform movements or tics). An antigen labelled D8/17, on the surface of peripheral blood mononuclear cells has been shown to be a marker for the genetic tendency to generate abnormal antibodies to GABHS. Two independent groups of researchers have found a greater expression of the D8/17 antigen in the B lymphocytes of patients with childhood-onset OCD or Tourette’s disorder compared with healthy controls, indicating that the presence of the D8/17 antigen may serve as a marker of susceptibility for OCD or tics.^{(62, 63)}