Clinical interviews and observations are the primary tool for establishing a tic disorder diagnosis, as there is no specific medical test presently available for tics. Current DSM-IV-TR nosology includes four diagnostic categories across the tic disorder spectrum: Tourette’s disorder (DSM-IV-TR term for TS), chronic motor or vocal tic disorder, transient tic disorder, and tic disorder not otherwise specified (American Psychiatric Association, 2000). TS is generally considered to be the most severe diagnosis and is characterized by at least a 12-month history of frequent tics, including multiple motor tics and at least one vocal tic, although they need not occur simultaneously. The tics must not be attributable to other factors such as a stereotypical movement disorder, a general medical condition, a known central nervous system disease (e.g., Huntington’s chorea), or substance intoxication. Chronic motor or vocal tics involve at least 12 months of frequent motor or vocal tics, respectively. Transient tic disorder, considered less severe, is characterized by mild tics that are present for at least 4 weeks but less than 12 months. Tics must begin prior to age 18 in order to meet criteria for each of these diagnoses. Finally, tic disorder not otherwise specified captures other clinically significant tic symptoms that do not meet criteria for one of the aforementioned diagnoses (e.g., insufficient duration of symptoms).

Tics are defined as “sudden, rapid, recurrent, non-rhythmic, and stereotyped” motor movements or vocalizations (American Psychiatric Association, 2000, p. 108), which draw on one or more muscle groups, mimic the experience of normal behavior, and are experienced as outside volitional control (Leckman, King, & Cohen, 1999). Within this relatively broad definition, tics may be categorized along various dimensions including type (motor or vocal), complexity (number of muscle groups involved), and degree of interference in functioning (none to severe). For example, simple motor tics involve isolated muscle groups in single anatomical locations and manifest as quick and meaningless muscle movements, such as eye blinking, nose twitching, facial grimacing, head jerking, and shoulder shrugging. Complex motor tics involve multiple muscle groups and manifest as slower and more purposeful movements, such as hand gestures, touching objects, touching self, bending, jumping, leg kicking, and hopping. Simple vocal tics comprise relatively quick and inarticulate sounds such as sniffing, coughing, grunting, and throat clearing. Finally, complex vocal tics comprise more intelligible vocalizations such as syllables, words, phrases, animal sounds, repetitions of others’ or own words, and speech atypicalities (Piacentini, Pearlman, & Peris, 2007). There is great inter-individual variability in tic symptom topography, as well as the degree of interference or impairment in functioning caused by tics (Kircanski, Woods, Chang, Ricketts, & Piacentini, 2010). Within individuals, symptom fluctuation is also typical (Coffey, Biederman, Geller, et al., 2000), and symptom exacerbation is often observed in response to physiological stressors (e.g., illness) and psychosocial stressors (e.g., peer and family conflicts) (Piacentini et al., 2007).

Transient tics are common in very young children, affecting around 12–18% of 5–7-year olds, while the prevalence of TS in the community is estimated at 0.6%, and the prevalence of chronic tic disorder is approximately 1–2% (Scahill, Sukhodolsky, Williams, & Leckman, 2005). The gender distribution of TS follows a 3:1 male to female ratio (Singer, 1994; Zohar et al., 1999), and tics appear to be more common among European Americans than African Americans or Latinos (Freeman et al., 2000; Zohar et al., 1999). In addition to co-occurring most frequently with OCD, tic disorders are also often comorbid with non-OCD anxiety disorders (Coffey, Biederman, Smoller, et al., 2000) and attention-deficit/hyperactivity disorder (ADHD) (Zohar et al., 1999).

Tics typically emerge in early childhood, often beginning with simple movements of the head and face (Leckman, 2003; Leckman, Bloch, Scahill, & King, 2006). The average age of onset of tics (ages 5–7; Leckman, Bloch, King, & Scahill, 2006 precedes the typical age of onset of obsessive–compulsive symptoms (ages 8–11; Hanna, 1995; Piacentini, Bergman, Keller, & McCracken, 2003; Rapoport, Swedo, & Leonard, 1992) and the median age of onset of OCD (age 19; Kessler, Berglund, Demler, Jin, & Walters, 2005). The developmental course of tics may involve a rostral-to-caudal progression of increasingly complex motor tics (Leckman, Zhang, & Vitale, 1998). Tics typically peak in middle childhood and may markedly reduce or disappear in adulthood (Leckman, 2003; Leckman, Bloch, Scahill, et al., 2006 studies demonstrate that approximately 25% of children diagnosed with TS will experience moderate to severe tics into young adulthood (Leckman et al., 1998).

Many individuals describe an urge or sensation immediately before the occurrence of a tic, referred to in the literature as a premonitory urge (Banaschewski, Woerner, & Rothenberger, 2003; Leckman, Walker, & Cohen, 1993). Performance of a tic may serve to satiate or at least temporarily quiet this premonitory urge (Bliss, 1980; Himle, Woods, Conolea, Bauer, & Rice, 2007; Leckman et al.). Conversely, attempts to resist performance of a tic may intensify the premonitory urge. The relationship between premonitory urge and tic has been likened to that between obsessions and compulsions in OCD (e.g., Shapiro & Shapiro, 1992), and in some cases, differentiating a tic urge from an OCD-related obsession can be quite difficult. The presence of premonitory sensations distinguishes tic disorders from other movement disorders such as Parkinson’s disease, Huntington’s chorea, and hemiballismus (Scahill, Leckman, & Marek, 1995). Importantly, however, there are developmental differences in the ability to report on tic behavior, and younger children may be less able to perceive or describe sensory or volitional aspects of their tic experiences (Banaschewski et al.; Woods, Piacentini, Himle, & Chang, 2005).

In addition to establishing a diagnosis, a clinical interview with the patient and collaterals (e.g., spouse, parent, and teacher) is one of the most valuable strategies for assessing various features of tic disorders. A thorough clinical interview should begin with gathering of general information regarding age of onset, course of symptoms, and family history of tic disorders. Additionally, information regarding the topography, frequency, intensity, and stability of initial tics is useful.

Several available self-report inventories of tics are easy to administer and can provide useful snapshots of tic number and frequency. These measures are generally less informative with regard to tic duration and impairment and interference from tic symptoms.

It is often helpful to include a measure of tic symptoms that, unlike clinical interviews and self-report inventories, is not reliant upon patient report. Direct observation procedures allow the clinician to obtain a more objective measure of tic expression. Recent research has shown that brief (e.g., 5-min) clinic-based observations can be stable and as informative as home-based observations (Himle et al., 2006). However, as tics are believed to be temporarily suppressible, and the expression of tics in a laboratory or clinical setting may not fully capture patients’ tic experiences in daily life, observational procedures should be regarded as a supplement to rather than a replacement of more traditional assessment procedures.

OCD is characterized by obsessions and/or compulsions that are distressing, time consuming (take more than 1 h/day), or cause clinically significant impairment (American Psychiatric Association, 2000). Obsessions are recurrent, persistent, and distressing thoughts, images, or impulses. Compulsions are repetitive behaviors or mental acts performed in response to obsessions in order reduce distress or avoid perceived harm. The majority of adolescent and adult patients view their symptoms as excessive, although this insight may not be present in younger patients.

As with tics, the topography of OCD symptoms is quite diverse. Common obsessions involve excessive concern about germs, contamination, and illness (Moore et al., 2007), fears harm to self or others, preoccupations with symmetry, moral and religious obsessions, intrusive sexual thoughts, and superstitious obsessions (Geller et al., 2001; Swedo et al., 1989). Common compulsions involve excessive and/or ritualized washing, checking, counting, touching, ordering, arranging, confessing, seeking reassurance, and mental rituals such as praying (American Psychiatric Association, 2000; Piacentini & Langley, 2004). Compulsions may be performed to alleviate anxiety, discomfort, disgust, or the sense that something is not “just right” (Leckman, Walker, Goodman, Pauls, & Cohen, 1994). As noted later in this discussion, the internal, sensory quality of the “just right” triggers may appear similar in nature to the premonitory urge for tics, a feature that requires careful differential diagnosis.

Although typical age of onset of OCD is from 8 to 11 years (Hanna, 1995; Piacentini et al., 2003; Rapoport et al., 1992), onset can occur as young as 2–3 years (Garcia et al., 2009; Freeman et al., 2003; Freeman, Garcia, & Coyne, 2008). Gender distribution tends to follow a 3:2 male to female ratio until adolescence when the distribution levels out (Swedo et al., 1989). OCD tends to be chronic, with 40% of children and adolescents meeting diagnostic criteria up to 15 years after initial identification and 20% exhibiting subclinical symptoms (Leonard et al., 1993; Stewart et al., 2004).

Differential diagnosis between tic disorder and OCD should begin with assessment methods and measures, such as those described above, which are sufficient to detect the presence or absence of each condition. In addition to a comprehensive assessment, particular attention to aspects of symptom presentation can be useful in establishing the presence versus absence of each disorder. As noted above, complex and seemingly ritualistic tics typically emerge later in the course of tic disorders, following the onset of simple tics, and are rarely the only tics present for a given patient. If, following a comprehensive assessment, these types of behaviors appear to be the only discernible symptoms, the clinician may question the presence of a tic disorder and whether these behaviors are better conceptualized as compulsions (Woods et al., 2008). Likewise, subjective anxiety and threat-related cognitive content are likely to accompany at least some obsessive–compulsive symptoms. If a patient exhibits only brief and purposeless repetitive behaviors in the absence of any cognitive or affective precursors, the clinician may consider whether tic disorder may be a more appropriate diagnosis.