|By Neal R. Swerdlow, MD, PhD, Sam Zinner, MD, Robert H. Farber, PhD, Cassie Seacrist, and Heidi Hartston|
There is clear overlap in the clinical symptoms of obsessive-compulsive disorder (OCD) and Tourette syndrome (TS). As a result, OCD (with or without tics) and TS (with or without obsessive-compulsive symptoms [OCS]) have been conceptualized to form a disorder spectruman overlapping set of phenotypes reflecting presumed commonality at the level of the underlying genetics and neuropathology. We identified the characteristics of a research sample of patients with OCD or TS, based on information obtained in semistructured clinical interviews, to examine the similarities and differences in the clinical symptoms across this spectrum. This sample conformed to known age-of-onset and sex distribution patterns for OCD and TS. Previously reported patterns of predominant aggressive and sexual obsessions and touching compulsions were observed in subjects with tic-related OCD, compared with non-tic-related OCD (ie, OCD alone). The majority of patients with tic-related OCD experienced horrifically violent obsessions that were less common in OCD alone and much less common in TS. Nonetheless, symptomatic and functional impairment in TS subjects was clearly related to the intensity of their OCS. The specific obsessions and compulsions associated with clinical impairment in TS differed from those associated with impairment in OCD. These results suggest that, despite the many overlapping dimensions of these disorders, the symptoms and associated impairment in "pure" OCD, tic-related OCD, and TS do not form a simple continuous spectrum.
Studies of the neurobiology of obsessive-compulsive disorder (OCD) and Tourette syndrome (TS) have been catalysts for hypotheses about brain circuitry, the genetics of mental illness, neuroimmune processes, and mind-brain interactions. While the conceptual linkage of OCD and TS has clearly stimulated models for understanding the brain, the specific relationship between these disorders at the clinical, neurobiological, and genetic levels remains somewhat elusive. Family studies have provided the greatest support for the notion that OCD and TS are fundamentally linked, perhaps even different phenotypic expressions of the same genetic diathesis.1,2 These studies have shown increased rates of TS among OCD probands and family members, and vice versa. In fact, if we believe that the prevalence of OCD is 2%3 and the prevalence of comorbid TS among these individuals is approximately 7%,4 then we are faced with the complex notion that the number of individuals with comorbid TS and OCD exceeds the total number of individuals with TS of any form, which is estimated to be approximately 1 in 1,000.5,6
Intuitive evidence for an OCD-TS linkage comes from the perceived interchangeability of sensory, cognitive, and motor elements of these disorders.7 Indeed, this clinical impression of phenomenologic fluidity has driven many of our models for an OCD-TS spectrum.8 Within these models, tic-related OCD (ie, OCD accompanied at some point by tics) has received attention as a potential intermediate phenotype between OCD and TS.9,10 This possible hybrid form of OCD shares some features of TS (ie, tics); may respond optimally to regimens that include medications that are effective for TS, but not OCD (eg, dopamine antagonists)11; and may have epidemiologic features (eg, age of onset, sex distribution) that are midway between OCD and TS.12 Other observations suggest that tic-related OCD is symptomatically distinct from "pure" OCD. Individuals with tic-related OCD are reported to be more likely to experience aggressive, religious, and sexual obsessions, as well as checking, counting, hoarding, and touching compulsions, compared with people with pure OCD.13-16
If there is a continuous OCD-TS phenotypic spectrum, there are obvious implications for genetic models and for the logistics of selection criteria for genetic and other studies of these disorders. Furthermore, continuity at a clinical and genetic level might be accompanied by important similarities at the level of the neurobiology of these disorders. In this case, the observed neurobiologic differences between OCD and TS might reflect artifacts of their phenotypes (ie, neurochemical consequences of anxiety secondary to obsessions, or of movements involved in rituals versus tics), while common features in their neurobiology may be more associated with a primary common basis for this spectrum.
We compared clinical profiles among patients with OCD (pure and tic-related) or TS (with and without comorbid OCD) who participated in ongoing studies in our facility. This review yielded support for findings from previous studies regarding specific symptoms associated with pure vs tic-related OCD. Overall, there was substantial evidence for discontinuities, in addition to continuities, among the clinical profiles of patients with OCD or TS. While these findings underscore areas of clinical overlap between these disorders, they do not support the model of a simple clinical spectrum relationship between OCD and TS.
Study Participants and Interviews
Subjects with OCD (n=103) or TS (n=61) were recruited from local advertisements to participate in research studies at the University of California, San Diego, Medical Center. Adult (>18 years of age) OCD subjects (n=103) were administered subsections of the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Third Edition-Revised,17 by two trained interviewers (N.S., H.H.) to assess the presence of psychotic disorders and to confirm a diagnosis of OCD. OCD subjects were also administered the Yale-Brown Obsessive Compulsive Scale (YBOCS)18 to determine the type and severity of obsessions and compulsions. For all YBOCS interviews, instructions were reviewed with the subject, the subject completed the YBOCS checklist, each checklist item was then reviewed with the subject by the interviewer, and when appropriate, the content of the symptom was documented on the checklist via the use of direct quotes from the subject. Adult TS subjects (n=50) were administered the YBOCS and Yale Global Tic Severity Scale (YGTSS)19 by trained interviewers (N.S., S.Z., R.F.) to characterize the type and severity of their tic symptoms, as well as their global impairment level. Clinical information from TS children (n=11) was obtained via the age-appropriate versions of the Children's YBOCS (C-YBOCS) and the Children's YGTSS (C-YGTSS). Diagnostic assessment in children was also aided by the use of the Diagnostic Interview Schedule for Children-Revised (DISC-R, version 2.3, modules A-E).20
Subjects were excluded from participation at the point of initial communication (screening phone interview) or upon questioning on the day of interview for a history of substance abuse or dependence, recreational drug use within 1 month prior to testing, schizophrenia in the subject or in a first-degree relative, head injury with loss of consciousness, severe medical illness, electroconvulsive therapy (ECT), or pregnancy. Most (84%) OCD and TS subjects underwent urine toxicology screening on the day of the interview, and results verified no recreational drug use. (In the remaining 16% of subjects, urine testing was not completed, often due to contamination obsessions; their results were examined separately and found to be representative of the urine-tested subjects.) Upon completion of the above clinical assessments, subjects participated in one of several psychophysiologic studies. Data from these measures have been reported elsewhere,21-25 but no report of the detailed clinical assessments of these participants has been published.
Using information obtained from the YBOCS interview, subjects were categorized based on the lifetime presence or absence of symptoms in any one of the major YBOCS subgroups of obsessions (aggressive, contamination, sexual, hoarding, religious, symmetry, and miscellaneous) or compulsions (cleaning/washing, checking, repeating, counting, ordering, hoarding, and miscellaneous). Based on published reports of the clinical importance of specific symptoms,13-16 subgroups were analyzed in greater detail by categorizing obsessions or compulsions based on the presence or absence of specific content (eg, aggressive symptoms with specific violent content, aggressive images, nonviolent intrusive images, touch/tap/rub compulsions, etc). In a small number of cases, clear categorization of symptom content could not be made (ie, type of violent act was not clearly identified); therefore, data were omitted from subsequent analyses (ie, not recorded as either present or absent). Subjects were also categorized on the basis of specific clinical variables, such as self-reported age at the time of first obsessive-compulsive symptoms (OCS) or TS symptoms, and a positive or negative history of tics among OCD subjects.
Among the 103 subjects with OCD, 18 were identified as having a clear history of tics (chronic motor tics, chronic vocal tics, or both), but did not meet diagnostic criteria for TS (first tics after age 21 years, or only one type of tic [motor or vocal]), and were categorized as "OCD + tic." In 39 subjects, a tic history was categorized as "equivocal" (subject unable to recall, or description of symptoms uncharacteristic of tics), and these subjects were categorized as "OCD ? tic." The remaining 46 OCD subjects stated unequivocally that they had never experienced tics, and were categorized as "OCD alone." Two methods were used to categorize TS patients. Subjects with a diagnosis of OCD (obsessions and/or compulsions, and scores >1 on YBOCS items 1, 2, 3, 6, 7, or 8) were categorized as "TS + OCD" (n=29). Those with significant OCS (C-YBOCST or YBOCST>=15) were categorized as "TS + OCS" (n=13), vs those without significant OCS (C-YBOCST or YBOCST<15), who were categorized as "TS - OCS" (n=19). Based on this information and the semistructured interview, subject subgroups included tic-related OCD (OCD + tic; n=18), non-tic-related OCD (OCD alone; n=46), OCD without certain tic history (OCD ? tic; n=39), TS + OCD (n=29), and TS alone (n=32).
|TABLE 1. DEMOGRAPHIC CHARACTERISTICS OF STUDY SAMPLE|
|OCD Alone||OCD ? Tic||OCD + Tic||TS + OCD||TS Alone|
|Mean age in years (SD)||35.04 (11.08)||34.82 (10.48)||32.22 (9.93)|
|28.74 (16.27)||29.85 (17.77)|
|Mean age at first symptoms, in years||13.02 (8.02)||13.28 (7.16)||9.39 (6.48)|
|7.88 (2.53)||7.31 (3.94)|
|Handedness (% right-handed)||82.2||87.2||94.4||85.2||93.9|
|Employment status (employed:unemployed)||1.46:1||1.07:1||1.8:1||4.3:1 11.0:1|
|*OCD overall--Male:Female=1.07:1; TS overall--Male:Female=3.07:1.||For subjects >18 years of age, excluding self-identified students, homemakers, and retirees.||OCD=obsessive-compulsive disorder; TS=Tourette syndrome; SD=standard deviation.|
|TABLE 2. CLINICAL RATING SCORES (MEAN)|
|OCD Alone||OCD ? Tic||OCD + Tic||TS + OCD||TS Alone|
|*P<0.10 P<0.0005 P<0.001|
|OCD=obsessive-compulsive disorder; TS=Tourette syndrome; O=obsession subscale; C=compulsion subscale; T=total score; M=motor subscale; P=phonic subscale; I=impairment subscale.|
Comparisons were designed to assess the relationship between OCD symptoms, their intensity, functional impact, and content across the specific clinical subgroups. The hypothesis was that a continuous disorder spectrum would be reflected by continuities (ie, conserved patterns) in the clinical features of OCD across these subgroups. The frequency of specific OCD symptom categories and symptom content were compared across the four diagnostic subgroups using chi-squared tests. Continuous variables, including YBOCS and YGTSS scores and subscores and age at symptom onset, were compared across the diagnostic subgroups and across groups characterized by the presence or absence of specific OCD symptoms using an analysis of variance. Simple regression analyses were used for correlations among continuous variables. The a level was 0.05; thus, P<=0.05 was considered significant.
|TABLE 3. CORRELATION MATRIX (R): YBOCS AND YGTSS|
|IN TS SUBJECTS|
|*P<0.10 P<0.0005 P<0.001|
|YBOCS=Yale-Brown Obsessive-Compulsive scale; YGTSS=Yale Global Tic Severity scale; O=obsession subscale; C=compulsion subscale; T=total score; M=motor subscale;|
|P=phonic subscale; I=impairment subscale.|
|FIGURE 1. Yale-Brown Obsessive Compulsive scale (YBOCS) scores (mean ± standared error of the mean [SEM]) in obsessive-compulsive disorder (OCD) subgroups (OCD alone, OCD ? tic, and OCD + tic) and Yale Global Tic Severity scale (YGTSS) scores (mean ± SEM) in Tourette syndrome (TS) specific obsessions and compulsions. Statistical differences are indicated at right, based on one-factor analysis of variance.|
Age, sex, age at first symptoms, handedness, and employment status are shown in Table 1. Among OCD subjects overall, the equal representation of males and females is consistent with previous reports.26 TS subjects overall were predominantly male; the ratio of 3.07 males to 1 female with TS (M:F overall TS group=46:15) is also comparable with that reported elsewhere.27-30 Age at symptom onset in both OCD and TS groups was also consistent with our understanding of these disorders.29,30 Both the sex ratio (M:F=2.6:1) and the mean age at first OCD symptoms (9.39 years) for the OCD + tic group were intermediate values between those determined for OCD alone and TS groups. Interestingly, the latter comparison primarily reflected the early age of first symptoms in females among the OCD + tic group (6.40 ± 1.95 mean ± standard deviation [SD]). Neither sex ratios nor age at first symptoms distinguished TS subjects with OCD (or OCS) from those without OCD (or OCS). Unemployment tended to be greater in OCD groups vs TS groups; among TS subjects, unemployment was more than 2.5 times higher among subjects with comorbid OCD compared with those without OCD.
Clinical Ratings and Impairment
Clinical rating-scale scores are seen in Table 2. Because both YBOCS and YGTSS ratings are disorder-specific by design, YBOCS data for participants with TS alone are reported only as a point of reference. Among OCD subjects, no significant differences in YBOCS total or subscale scores were observed between the OCD alone vs the OCD + tic groups. TS + OCD subjects had lower YBOCS scores compared with all other OCD groups. Compared with TS alone subjects, TS + OCD subjects scored significantly higher on the YGTSS total scale (F=12.74; df 1,56; P<0.001), accounted for largely by greater YGTSS impairment scores in these subjects (F=14.39; df 1,56; P<0.0005), with only trends toward greater scores in motor (F=2.87; df 1,56; P<0.10) and phonic (F=3.50; df 1,56; P<0.07) subscales. Similar patterns were evident when TS subjects were categorized on the basis of YBOCS >=15. A 3 x 4 regression matrix yielded significant correlations between YGTSS total score and YGTSS impairment score with YBOCS total score, obsession subscale score, and compulsion subscale score among individuals with TS (Table 3). Interestingly, the relationship between YGTSS impairment scores and these measures of OCS severity was generally as robust as the relationship between YGTSS impairment and YGTSS motor (R=0.46), phonic (R=0.36), or total tic (R=0.50) scores. Thus, while the presence of tics was not associated with a more "malignant" form of OCD, based either on symptom ratings (YBOCS) or one functional measure (employment), the presence of obsessions or compulsions in TS was associated with a more severe condition with clear impairment in both symptom and functional domains.
Additional evidence for a relationship between YBOCS elevation and functional impairment in TS subjects is the comparison of YBOCS scores among TS adults who were employed vs unemployed (mean [standard error of the mean (SEM)] YBOCST employed vs unemployed=9.15 [1.45] vs 18.75 [5.30]; F=5.79; df 1,23; P<0.025). Elevations in both obsession and compulsion YBOCS subscales were associated with unemployment in TS subjects, but interestingly, neither motor, phonic, nor total tic subscores of the YGTSS differed significantly between employed vs unemployed TS subjects (F=1.83, 2.05, and 2.38, respectively; P=not significant). In other words, as measured by the YGTSS impairment subscale and by a critical functional measure (employment), impairment in TS subjects was closely linked with the intensity of OCS. This relationship was at least as strong, and perhaps stronger, than the link between functional impairment and tics in these subjects.
|Table 4. Percent of Subjects Endorsing Lifetime History of Specific Obsessions and Compulsions|
|OCD Alone||OCD + Tic||TS + OCD||TS Alone|
other than blurt/embarrass
|SROC: 0.63* 0.35 0.63*
OCD=obsessive-compulsive disorder; TS=Tourette syndrome; SROC=Spearman Rank Order Correlation.
Symptom Features Across Subgroups
The percentage of subjects from each major diagnostic subgroup who endorsed the lifetime presence of specific obsessions and compulsions is described in Table 4. Compared with OCD alone subjects, more OCD + tic subjects endorsed sexual obsessions ([chi]2=5.07; P<0.025) and touch/tap/rub compulsions ([chi]2=15.13; P<0.0001). The prevalence of aggressive obsessions overall did not differ statistically among the OCD alone (86%) and OCD + tic groups (100%) ([chi]2=2.80; P<0.10). This likely reflected a "ceiling effect," as analysis of the relatively more severe aggressive obsessions revealed these to be much more common in OCD + tic subjects.
To increase the sensitivity of this comparison, aggressive obsessions were categorized according to their specific content in a manner that formed an intensity gradient with the following obsessions: (1) any aggressive obsession; (2) aggressive obsession other than embarrassment/blurting concerns; (3) a specific violent act; and (4) "worst-case scenario" (eg, stabbing, maiming, or killing, etc). Intrusive violent images were also categorized separately, but their content severity ranged from mild (eg, image of hitting mother) to severe (eg, mutilation scene). When assessed along this intensity gradient, OCD + tic subjects were significantly more likely to have experienced aggressive obsessions other than embarrassment/blurting concerns ([chi]2=6.24; P<0.015) and aggressive obsessions in which a violent act was involved ([chi]2=7.70; P<0.006), particularly when it included the worst-case scenario ([chi]2=12.42; P<0.0005). OCD + tic subjects were also marginally more likely than OCD alone subjects to report intrusive violent images ([chi]2=4.95; P<0.03), and trends were observed for OCD + tic subjects to report more nonaggressive images, as well as blink/stare compulsions, consistent with previous reports.13,14 OCD alone and OCD + tic groups did not differ significantly in the likelihood of experiencing any other obsessions or compulsions (see Table 4).
To examine the other side of the OCD-TS spectrum, obsessions and compulsions were compared among the OCD + tic group and the TS + OCD and TS + OCS groups (see Table 4). Compared with TS + OCD subjects, OCD + tic subjects were more likely to have experienced any aggressive symptom ([chi]2=7.55; P<0.01), at any level of severity: aggressive other than embarrassment/blurting ([chi]2=13.53; P<0.0005), aggressive + violent act ([chi]2=11.85; P<0.001), and aggressive + stab/maim/kill ([chi]2=13.46; P<0.0005). These groups did not differ in the prevalence of intrusive violent images ([chi]2<1). Similar patterns were evident in the comparison between OCD + tic and TS + OCS groups (not shown). Examples of aggressive obsessions in OCD + tic and TS + OCD subjects are seen in Table 5. Compared with TS + OCD subjects, OCD + tic subjects were also more likely to have endorsed religious obsessions ([chi]2=4.04; P<0.05), cleaning/washing compulsions ([chi]2=6.53; P<0.02), counting compulsions ([chi]2=6.52; P<0.02), intrusive nonviolent sounds or images ([chi]2=5.54; P<0.02), and touch/tap/rub compulsions ([chi]2=3.82; P=0.05).
To examine the possibility that some of the differences in obsessive-compulsive (OC) symptoms between OCD + tic and TS + OCD subjects simply reflected the greater severity of OCD (as measured by higher YBOCS scores) in OCD + tic subjects, subgroups of 10 OCD + tic and 10 TS + OCD subjects were matched for YBOCST scores (mean [SEM] YBOCS: OCD + tic=20.3 [1.13]; TS + OCD=19.4 [1.41]) and the prevalence of obsessions and compulsions were compared between these subgroups. Despite the reduced sample sizes in this subgroup comparison, significant group differences persisted among the aggressive obsessions, which remained more common among OCD + tic subjects: aggressive other than embarrassment/blurting ([chi]2=4.92; P<0.03), aggressive + violent act ([chi]2=7.29; P<0.007), and aggressive + stab/maim/kill ([chi]2=8.56; P<0.005). All other symptom differences noted in the unmatched group comparisons either disappeared or were reduced to "trend" levels among these matched groups. Thus, while some differences in OCD symptoms between OCD + tic and TS + OCD groups may reflect the greater severity of OCD in OCD + tic subjects, the distinct profile of aggressive symptoms appears to reflect a categorical difference between these two types of illnesses.
The lifetime prevalence of specific obsessions and compulsions was compared in TS + OCD vs TS alone groups (see Table 4). Because these groups were distinguished by the presence of an OCD diagnosis, it was anticipated that most obsessions and compulsions would be relatively more common in the TS + OCD group. Surprisingly, only four OCD symptoms were significantly more common in the TS + OCD group: sexual obsessions ([chi]2=17.27; P<0.0001), checking compulsions ([chi]2=8.79; P<0.005), repeating compulsions ([chi]2=5.46; P<0.02), and touch/tap/rub compulsions ([chi]2=4.95; P<0.03). Similar patterns were evident when TS subjects were categorized on the basis of YBOCS >=15.
A rank order of most to least common obsessions and compulsions among the major diagnostic subgroups was tabulated. While aggressive obsessions of all severities were among the most common symptoms in OCD + tic subjects, the most common symptoms in TS + OCD subjects were checking, touch/tap/rub compulsions, and repeating compulsions, with the most extreme violent obsessions being the least common symptom in this group. Spearman Rank Order Correlation of symptoms revealed significant correlations in comparisons of OCD alone vs OCD + tic groups (R=0.63, P<0.01), and of TS + OCD vs TS alone groups (R=0.63, P<0.01), but not of OCD + tic vs TS + OCD (R=0.35, P=NS) (see Table 4).
Obsessions and compulsions associated with relatively more severe symptom rating scores among the major diagnostic subgroups are seen in Figure 1. Among OCD subjects as a whole, elevated YBOCS scores were seen in subjects endorsing the lifetime presence of symmetry obsessions, washing/cleaning compulsions, or repeating compulsions. Interestingly, aggressive obsessions of any severity were not associated with elevated YBOCS scores in OCD subjects. In sharp contrast, among TS subjects, elevated YGTSS scores were seen in subjects endorsing a lifetime presence of aggressive obsessions of any kind; YGTSS scores increased in proportion to the degree of aggressive content (see Figure 1). Elevated YGTSS scores in TS subjects were also associated with a history of sexual obsessions or repeating or counting compulsions. Intuitively, one might predict that increased YGTSS scores associated with violent or sexual obsessions might primarily reflect elevations on the impairment subscale, while YGTSS elevations associated with counting and repeating obsessions might reflect elevated scores on the phonic and motor subscales, respectively (ie, because of the phonic component of counting, and the motor component of repetitive movements). However, this was not the case. A history of aggressive or sexual obsessions in TS subjects was associated with elevated scores on all YGTSS subscales, including motor and phonic subscales (aggressive obsessions: motorF=11.68; df 1,53; P<0.002, phonicF=5.30; df 1,53; P<0.03; sexual obsessions: motorF=5.77; df 1,56; P<0.02, phonicF=4.23; df 1,56; P<0.05). A history of repeating compulsions was associated with elevated scores on YGTSS phonic (F=5.02; df 1,56; P<0.03) and impairment subscales (F=5.49, df 1,56; P<0.025), but not on the motor subscale, while a history of counting compulsions was associated only with elevations on the impairment subscale (F=6.74; df 1,56; P<0.015). Thus, there is little overlap between the types of obsessions and compulsions associated with the more clinically malignant forms of OCD and TS.
|Table 5. Sample of Content of Aggressive Obsessions in Individuals With OCD + Tics (n=11) vs TS + OCD (n=7)|
|Diagnosis||Content of Aggressive Obsession|
|OCD, CMT||Images: hitting head on sharp corner causing skull to open and brain to fall out; murdering babies, sister with ax; stepping off curb, being run over, causing evisceration|
|OCD, CMT||Images: extends neck until "throat bursts through skin"; daughter's fingers cut off, cat with leg cut off|
|OCD, CMT||Images: mother crashing car and burning to death|
|OCD, CMT||Images: putting gun in mouth; fear of house burning down with people inside|
|OCD, CMT||Fear of stabbing, lacerating people with knives; fear of running people over with car|
|OCD, CMT||Images: killing parents; hanging self; jumping from building|
|OCD, CMT||Fear of stabbing someone with knife in kitchen|
|OCD, CVT||Image: hugs mother, mother's head falls off, decapitated head and trunk|
|OCD, CVT||Images: runs razor blade down arm, slicing it open; runs over woman with baby in crosswalk|
|OCD, TD NOS*||Images: being cut up by chain saw; piercing hand with knife or stick; child being run over|
|OCD, CVT||Images: cracking father's head with hammer; fears of strangling child; stabbing someone|
|TS, OCD||Fear of saying swear word or something embarrassing|
|TS, OCD||Fear of falling in front of friends and becoming embarrassed; fear of hitting mother|
|TS, OCD||Excessive worries about health of others; fear of stealing something
Image: "gruesome pictures" of friends, relatives
|TS, OCD||Fear daughter will throw up at school or become ill|
|TS, OCD||Consumed by thoughts of animals being neglected or abused; thinks about people dying|
|TS, OCD||Fear of introducing someone by the wrong name|
|TS, OCD||Image: hitting or stabbing someone unfamiliar|
|<||*Tic disorder, not otherwise specified; continuous motor and vocal tics starting at age 41 years.|
|OCD=obsessive-compulsive disorder; TS=Tourette syndrome; CMT=chronic motor tic; CVT=chronic vocal tic.|
There are arguably more differences than similarities between TS and OCD. OCD is 40 times more common than TS.5,6 TS is three to four times more common in males than in females, whereas in pure OCD, sex patterns are balanced.26,30 TS typically is diagnosed at about age 7 years, compared with age 20 years for OCD.29,30 While these ages represent group means, and there are overlapping subpopulations (eg, see age of first symptoms of OCD + tic group, present study), on average, the state of the nervous system at the most common times of presentation of these disorders is quite different.31 Recent data suggest that tic symptoms may decline in severity substantially by the early 20s in a large proportion of TS patients,32 but no obvious parallel course is known in OCD. There is no overlap in the primary medications used to manage these disorders.26,30 Neuroimaging studies, though not unanimous in their conclusions, suggest opposite patterns of brain metabolism within cortico-striato-pallido-thalamic (CSPT) circuitry in OCD vs TS (ie, cortico-striatal hypermetabolism and hyperperfusion in OCD33,34 vs CSPT hypometabolism and hypoperfusion in TS35-41).
Substantial literature exists describing in great detail and via creative analytical approaches the clinical boundaries of OCD and TS. Many of the present findings are simply confirmatory of these previous reports, related to demographics and specific symptoms associated with OCD alone, OCD + tic, TS + OCD, and TS alone populations. However, several new findings emerged from the present data that may add to our understanding of the relationship between OCD and TS. One parsimonious interpretation of these data (albeit an extreme one) is that within this sample, OCD alone, OCD + tics, and OCD + TS represent at least two, and perhaps three, different types of OCD. The differences among these OCD types were both quantitative and qualitative.
Quantitative differences were found in the intensity of OCD symptoms, per se; substantially higher YBOCS scores were associated with OCD alone or OCD + tic subgroups compared with the TS + OCD subgroup. A simple interpretation of this finding is that time, energy, distress, and other functional costs of OCD symptoms, as assessed by the YBOCS, are more prominent in non-TS forms of OCD. A sharp counterpoint to this finding is the fact that for TS subjects, the presence of even this milder form of OCD was associated with clear functional impairment. OCD symptoms may even have been more disabling in these TS patients than were the symptoms of TS. YGTSS impairment scores were substantially higher in TS + OCD vs TS alone subjects, and correlated significantly with YBOCS total and subscale scores. Unemployment rates for TS + OCD subjects were 2.5 times higher than unemployment rates in TS alone subjects, and unemployed TS + OCD subjects were characterized by higher YBOCS scores, but not higher YGTSS scores compared with TS alone subjects.
Qualitative differences in OCD were also observed among the different clinical subgroups. Most obvious were the differences in the content of aggressive obsessions. OCD + tic subjects were quite distinct among these subgroups in almost uniformly endorsing the lifetime presence of aggressive obsessions with severe violent content. By comparison, such symptoms were much less common in OCD alone and TS + OCD, and almost nonexistent in TS alone (only 4% endorsed the most severe violent obsessions). This unique feature of OCD + tic subjects was not simply a reflection of worse OCD; subgroup differences persisted even among samples matched for YBOCS scores. Likewise, the presence of violent obsessions was not a simple correlate of tics; these obsessions were quite rare in TS of any form, with or without OCD. Rather, these particularly violent obsessions appeared as a discontinuity in the OCD-TS spectruma signal expression, perhaps reflecting something different about the neurobiology of the OCD + tic subgroup.
Viewed from the perspective of relative prevalencehow common specific symptoms were within individual subgroupsOCD + tic subjects and OCD alone subjects reported similar "ranks" or symptoms, as did TS + OCD and TS alone subgroups. In contrast, the rank lists of the middle portions of the spectrumthe OCD + tic and TS + OCD groupswere not significantly correlated. However, this profile of symptom ranks does not provide a full image of the impact of specific obsessions and compulsions among the different clinical subgroups. Surprisingly, the more common violent, mutilating obsessions were not accompanied by elevated symptom scores in OCD + tic subjects compared with OCD alone subjects. Even among all OCD subjects (with or without tics), violent obsessions were not associated with higher YBOCS scores. In contrast, while they were less common among TS subjects, violent obsessions were clearly associated with elevated YGTSS scores, in all subscales, with the relative degree of violent content associated directly with the degree of YGTSS elevation. Aggressive and sexual obsessions were not associated with elevated YBOCS scores in OCD subjects, but were associated with more overall life impairment in TS subjects, as well as higher scores for motor and phonic tics. There was little overlap between the OCD symptoms associated with elevated YBOCS scores in OCD subjects, and those associated with elevated YGTSS scores in TS subjects: Only one symptomrepeating compulsionswas associated with higher overall symptom ratings in both OCD and TS subjects.
Overall, the current data may present a challenge to the notion of a continuous spectrum connecting OCD and TS. Added to the list of distinguishing characteristics between these disorders, there appear to be substantial qualitative and quantitative differences in the types of obsessions and compulsions, and the functional impact of these symptoms, between OCD and TS subjects. Presumably, these clinical differences reflect differences in the neurobiology of these disorders, in either the location or nature of regional brain disturbances causing obsessions and compulsions in OCD, and those causing obsessions and compulsions in TS. While the origin of these symptoms in both disorders may lie within CSPT circuitry, something distinguishes the specific content and associated impairment of these symptoms in OCD and TS. However subtle such a difference might be at the level of brain circuitry, the present data suggest that there are substantive differences experienced at the level of quality of life.
The present data must be viewed critically. This clinical sample was obtained as part of a research study, and recruitment bias may favor very impaired subjects, whose symptoms may not be representative of the general clinical population. Both YBOCS and YGTSS scores in this sample were within the range of scores reported in other research samples,33,42 and sex, age of onset, and employment characteristics for the present subjects were also similar to those reported in previous studies. Although the level of unemployment among nonstudent/homemaker/retiree OCD subjects in this sample was quite high (46.4%), this figure was consistent with previous reports in a primary-care population.43,44 Finally, many of the specific findings related to symptom prevalence among the present sample subgroups were consistent with previous reports. Still, it is clearly possible that idiosyncratic sample characteristics of subjects presenting for research in a tertiary-care setting may limit the generalized relevance of these findings.
Sampling issues aside, the design of the present study (essentially a chart review) precludes firm conclusions regarding the causal relationship between several of the reported associations, and more importantly, regarding the treatment implications of these findings. For example, it is not clear whether obsessions and compulsions worsen TS, or whether the more malignant forms of TS (those associated with greater impairment and unemployment) carry with them neuropathologic consequences responsible for the generation of obsessions and compulsions. Even this simple causal link (which cannot be demonstrated by these data) would have obvious and important treatment implications: If obsessions and compulsions worsen TScausing more tics, as well as life impairmentthis might provide a rationale to treat TS with primary anti-OCD medications (with or without primary antitic medications), even if the degree of OC symptomatology does not meet diagnostic criteria for OCD. Of course, such a strategy assumes that the obsessions and compulsions of TS would respond clinically to the same medications that effectively treat obsessions and compulsions in OCD, and the present data cannot address this assumption.
More generally, the present data may provide some impetus to rethink the notion of the OCD spectrum. If there are discontinuities in important clinical features of the two most biologically linked members of the OCD spectrumOCD and TSwhat can be said about the clinical continuum linking compulsive gambling, bodybuilding, shopping, shoplifting, sexual behavior, autism, "schizo-OCD," eating disorders, and many other present members of, and future applicants to, the OCD spectrum? Perhaps the most conservative assessment is that the human cognitive and behavioral repertoire can be categorized along many dimensions (eg, repetitive, ego-dystonic, impulsive, etc), and that when problems arise in the brain, changes occur across these dimensions. When any one of several different types of problems arise within a similar brain circuit (eg, CSPT circuitry), then some similarities are bound to emerge among the cognitive and behavioral dimensions controlled by that brain circuit. When these problems reflect insults within a fairly narrow developmental period (eg, the first 2 decades of life), then these clinical similarities may appear more pronounced; they may even respond, more or less, to the same classes of medications, or become material for similar developmental or dynamic interpretations. Does this make a spectrum or a collection? The use of dimensional similarities to unite collections of neuropsychiatric disorders may offer advantages for describing clinical phenomena by analogy, but it also risks diluting power in genetic, neuropathological, and pharmacotherapeutic studies of these disorders. The present data may not significantly shift this cost:benefit ratio for the OCD spectrum, but perhaps, these data support the need to consider it carefully.
Acknowledgments: Studies were supported by National Institute of Mental Health grants MH 01436, MH 54621, MH 42228, and an Independent Investigator Award to N.R.S. from the National Alliance for Research on Schizophrenia and Depression. The authors are very grateful to Drs. James Leckman and John Walkup for their insightful comments, and to Ms. Pamela Auerbach and Ms. Alyson Hansen for their assistance in manuscript preparation. A discussion of some of these data was described in modified form in a published interview with the first author.45
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