Disentangling the Overlap between Tourette's Disorder and ADHD

J. Child Psychol. Psychiat. Vol. 39, No. 7, pp. 1037–1044, 1998

Cambridge University Press

' 1998 Association for Child Psychology and Psychiatry

Printed in Great Britain. All rights reserved

0021–9630}98 $15.00­0.00

Disentangling the Overlap between Tourette’s Disorder and ADHD

Thomas Spencer and Joseph Biederman

Massachusetts General Hospital and Harvard Medical School, Boston, U.S.A.

Margaret Harding and Deborah O’Donnell

Massachusetts General Hospital, Boston, U.S.A.

Timothy Wilens

Massachusetts General Hospital and Harvard Medical School, Boston, U.S.A.

Stephen Faraone

Massachusetts General Hospital, Boston, Harvard Medical School, Boston, and Harvard Institute of Psychiatry,Epidemiology and Genetics, Brockton-West Roxbury Veterans’ Affairs Medical Center, U.S.A.

Barbara Coffey and Daniel Geller

Massachusetts General Hospital, Boston, Harvard Medical School, Boston, and McLean Hospital, Belmont, U.S.A.

Objective : To identify similarities and differences in neuropsychiatric correlates in childrenwith Tourette’s syndrome (TS) and those with ADHD. Method : The sample consisted ofchildren with Tourette’s syndrome with ADHD (N¯ 79), children with Tourette’s syndromewithout ADHD (N¯ 18), children with ADHD (N¯ 563), psychiatrically referred children(N¯ 212), and healthy controls (N¯ 140). Results : Disorders specifically associated withTourette’s syndrome were obsessive compulsive disorder (OCD) and simple phobias. Ratesof other disorders, including other disruptive behavioral, mood, and anxiety disorders,neuropsychologic correlates, and social and school functioning were indistinguishable inchildren with Tourette’s and ADHD. However, children with Tourette’s syndrome plusADHD had more additional comorbid disorders overall and lower psychosocial functionthan children with ADHD. Conclusions : These findings confirm previously noted associ-ations between Tourette’s syndrome and OCD but suggest that disruptive behavioral, mood,and anxiety disorders as well as cognitive dysfunctions may be accounted for by comorbiditywith ADHD. However, Tourette’s syndrome plus ADHD appears to be a more severecondition than ADHD alone.

Keywords: Tourette’s syndrome, attention deficit disorder, adolescence, school children,comorbidity.

Abbreviations: GAF: Global Assessment of Functioning scale ; OCD: obsessive compul-sive disorder ; ODD: oppositional defiant disorder ; TS: Tourette’s syndrome; WRAT:Wide Range Achievement Test.

Introduction

Tourette’s syndrome is a chronic neuropsychiatric con-dition commonly associated with social, occupational,and academic dysfunction (Erenberg, Cruse, & Rothner,1986; Stokes, Bawden, Camfield, Backman, & Dooley,1991). Although its etiology remains unknown, genetic

Requests for reprints to: Dr Thomas Spencer, Pediatric Psy-chopharmacology Unit (ACC-725), Massachusetts GeneralHospital, Fruit Street, Boston, MA 02114, U.S.A.

and psychosocial factors have been implicated in itsdevelopment (Leckman & Peterson, 1993; Pauls, 1992b).

Children with Tourette’s syndrome have frequentlybeen found to have high levels of comorbidity withobsessive compulsive disorder (OCD) and attention-deficit}hyperactivity disorder (ADHD). The high levelsof comorbidity between Tourette’s syndrome and OCDare not surprising considering that they are thought torepresent variable expressivity of the same underlyingrisk factor, based on the work of Pauls et al. (Pauls,1992a). Although the reasons for the comorbidity withADHD are less clear, all studies of Tourette’s syndrome

1037

1038 T. SPENCER et al.

have reported very high rates of ADHD in patients withTourette’s (Bruun, 1984; Comings, 1995; Comings &Comings, 1985, 1987b, 1990; Erenberg & Rothner, 1978;Erenberg et al., 1986; Fernando, 1967; Jagger et al.,1982; Moldofsky, Tullis, & Lamon, 1974; Pauls, Leck-man, & Cohen, 1993; Pauls et al., 1986; Shapiro, Shapiro,Bruun, & Sweet, 1978; Shapiro, Shapiro, Young, &Feinberg, 1988; Singer & Rosenberg, 1988; Spenceret al., 1995; Stefl, 1984; Stokes, Bawden, Camfield,Camfield, & Salisbury, 1995; Sverd, Curley, Jandorf,& Volkersz, 1988; Wilson, Garron, Tanner, & Klawans,1982).

In recent years, data have emerged indicating an evenwider spectrum of psychiatric and cognitive correlates inpatients with Tourette’s syndrome, which include moodand anxiety disorders and neuropsychological deficits.For instance, several studies reported a high incidence ofdepression (Comings & Comings, 1987a; Pauls, Leck-man, & Cohen, 1994; Robertson, Trimble, & Lees, 1988)and mania (Comings & Comings, 1987a; Kerbeshian,Burd, & Klug, 1995), as well as prominent anxiety(Coffey, Frazier, & Chen, 1992; Comings & Comings,1987d; Erenberg, Cruse, & Rothner, 1987; Pauls et al.,1994) in patients with Tourette’s syndrome.

However, comorbidities with mood and with anxietydisorders, as well as with neuropsychological impair-ments have also been associated with ADHD (Bieder-man, Newcorn, & Sprich, 1991; Caron & Rutter, 1991;Faraone et al., 1993; Seidman et al., 1995). Thus,questions remain as to whether neuropsychiatric corre-lates associated with Tourette’s syndrome are due to thesyndrome itself or to the comorbidity with ADHD.

Disentangling the overlap between Tourette’s syn-drome and ADHD can have important clinical conse-quences. Although the mainstay of pharmacologicaltreatment of Tourette’s syndrome (antipsychotics) havebeen shown to have some efficacy for the behavioralsymptoms of ADHD, because of risks for tardivedyskinesia as well as a lack of cognitive enhancement theyare not the treatment of choice for ADHD (Gittelman-Klein, Klein, Katz, Saraf, & Pollack, 1976). Althoughrecent work by Gadow and colleagues (Gadow, Sverd,Sprafkin, Nolan, & Ezor, 1995; Sverd, Gadow, Nolan,Sprafkin, & Ezor, 1992; Sverd, Gadow, & Paolicelli,1989) provides some measure of reassurance aboutexacerbation of tics by stimulants, other studies havereported tics worsening in up to 30% of children withADHD who have comorbid tics (Caine, Ludlow,Polinksy, & Ebert, 1984; Comings & Comings, 1988;Denckla, Bemporad, & MacKay, 1976; Erenberg, 1982;Erenberg, Cruse, & Rothner, 1985; Golden, 1977, 1982;Konkol, Fischer, & Newby, 1990; Price, Leckman, Pauls,Cohen, & Kidd, 1986; Shapiro & Shapiro, 1981).Although no longer strictly contraindicated, until more isknown, experts continue to advise caution in the use ofstimulants in children with ADHD and tics (Castellanoset al., 1997). Thus, disentangling the overlap betweenADHD and Tourette’s syndrome may facilitate the riskbenefit analysis of appropriate interventions for ADHDin patients with Tourette’s syndrome. To this end, weevaluated the neuropsychiatric correlates of children withTourette’s syndrome and commonality with those ofADHD. Based on the available literature we hypothe-

sized that OCD and ADHD would be highly prevalent inpatients with Tourette’s syndrome and that comorbiditywith OCD will be specific to Tourette’s syndrome.

Methods

The sample consisted of children, aged 18 years or younger,with Tourette’s syndrome or with ADHD, referred to apediatric psychopharmacology clinic. Of these, 44% weretreatment naive. Additionally, we identified two comparisongroups: psychiatrically referred children without ADHD or ticsfrom the same clinic and healthy children without ADHDascertained from ongoing family genetic studies of boys andgirls with ADHD (Biederman et al., 1992, 1996). The insti-tutional review board approved the chart review of outpatientsin a pediatric psychopharmacology clinic and the use of datafrom healthy children enrolled in the family genetic studies. Forcomparison the psychiatrically referred group was matched tothe other psychopathologic groups for age, socioeconomicstatus, and gender. Although psychiatrically referred childrenwithout ADHD or tics were included for reference, the primarycomparisons were between the Tic and ADHD groups.

All subject were assessed with identical methodology(Biederman et al. 1992, 1996). Psychiatric assessments ofprobands relied on the Kiddie SADS-E (Epidemiologic Ver-sion) (Orvaschel & Puig-Antich, 1987). Diagnoses were basedon interviews with the mothers ; children were not directlyinterviewed. These semistructured diagnostic interviews wereadministered by trained raters. The interviewers had under-graduate degrees in psychology and were trained to high levelsof inter-rater reliability. Before working independently, inter-viewers observed interviews by experienced interviewers andclinicians. They subsequently conducted at least six practiceinterviews and at least two study interviews while beingobserved by senior interviewers.

We computed k coefficients of agreement by having threeexperienced, board-certified child and adult psychiatrists di-agnose subjects from audiotaped interviews made by theassessment staff. Based on 173 interviews, the median k was ±86.The ks were ±99 for ADHD and 1±0 for the diagnoses of tics andTourette’s syndrome. All diagnoses were reviewed by a di-agnostic sign-off committee of board-certified child and adultpsychiatrists. The committee reviewed the items endorsedduring the interview along with detailed notes taken by theinterviewer.

Raters were blind to the clinical diagnosis apart from theirknowledge that the child in the Clinic sample was seen forgeneral psychiatric evaluation. As in our previous work(Biederman et al., 1992), major depression was diagnosed onlywhen full criteria were associated with severe impairment. Also,we use two or more anxiety disorders to index the presence of aclinicallymeaningful anxiety syndrome (Biederman et al., 1990).Rates of disorders reported here are lifetime prevalences. Forevery disorder a rating of severity was assessed that ranged froma score of 1 (mild) to 3 (severe).

The following interview questions are used in the K-SADS toelicit responses for the tic module : (1) Did your child ever haveany frequent, jerky, repetitive motor movements such as lipsmacking or frequent eye blinking? Other repetitive movementsof the face or body (not rhythmic or fidgeting)? What abouttouching or squatting? (2) Did he ever have vocal tics (grunts oryelps), or uttering obscenities? (3) Do the tics (or grunts) occurmany times a day (usually in bouts), nearly every day orintermittently throughout a period of more than one year? (4)Does the severity and location of the tics change over time? (5)Was he}she ill at the time the tics occurred? and (6) Was he}sheabusing drugs or alcohol at the time the tics occurred?

To be given a diagnosis of Tourette’s syndrome the subjectmust have had both a vocal tic and multiple motor tics many

1039DISENTANGLING THE OVERLAP BETWEEN TOURETTE’S DISORDER AND ADHD

times a day, nearly every day or intermittently throughout aperiod of more than 1 year. Patients with chronic tic disorder(either motor or vocal tics but not both) or transient tics (lessthan 1 year duration) were excluded from analysis.

In addition to assessment of psychopathology, we obtainedinformation regarding neuropsychologic functioning. Aca-demic achievement was assessed with the Wide Range Achieve-ment Test (WRAT; reading and arithmetic ; Jastak & Jastak,1985). Cognitive functioning was assessed with the vocabulary,block design, arithmetic, digit span, and digit symbol subtests ofthe Wechsler Intelligence Scales-Revised (WISC-R). We esti-mated Full Scale IQ from the vocabulary and block designsubtests and computed the Freedom From Distractibility IQfrom the other subtests (Sattler, 1988).

We used the procedure recommended by Reynolds 1984) todefine learning disabilities (Faraone et al., 1993). To evaluateschool functioning, we assessed—based on parent reports—three straightforward indices of school failure : placement inspecial classes, in-school tutoring, and repeated grades. Psy-chosocial functioning was assessed with the Global Assessmentof Functioning (GAF) scale of the DSM-III-R (1¯worst, 90¯best) (Spitzer, Williams, Gibbon, & First, 1990). Socioeconomicstatus (SES) was measured using the four-factor Hollingsheadscale (1¯highest, 4¯ lowest) (Hollingshead, 1975).

Categorical data were analyzed by chi-square analysis,continuous data by analysis of variance or multinominal logisticregression, and ordinal data by ordinal logistic regression asindicated. Associations between continuous variables wereevaluated using Pearson correlations. Statistical significancewas defined at the 1% level, with trends reported at the 5% leveland all tests were two-tailed. Data are expressed as mean³SDunless otherwise stated.

Results

We identified 97 children with Tourette’s syndrome,(TS group), 563 children with ADHD (ADHD group),and 212 psychiatrically referred children. One hundredand forty healthy controls were included for contrast butnot for statistical analysis. As described above (Methods),the psychiatrically referred group was matched to theother psychopathologic groups on demographic vari-ables. There was a high rate of ADHD in the TS group(81%). In order to compare homogenous groups, weseparated the TS with ADHD from the TS withoutADHD subjects into separate groups. Since the TSwithout ADHD group was small with limited statisticalpower, we employed dual omnibus analyses of all vari-ables, comprised of all psychopathic groups with (df¯ 3)and without (df¯ 2) the TS minus ADHD group.

After splitting the TS group, the four psychopathologic

Table 1Demographics

TS minusADHD(N¯ 18)

TS plusADHD(N¯ 79)

ADHD(N¯ 563)

Psychiatriccontrols

(N¯ 212)

Normalcontrols

(N¯ 140)Significance

(p)

Mean SD Mean SD Mean SD Mean SD Mean SD 3df 2df

Age 11±9 2±8 10±7 3±2 10±4 3±7 11±1 3±1 11±7 3±6 n.s n.s.SES 2±2 0±9 2±1 1±1 1±9 1±1 1±9 1±0 1±6 0±8 n.s. n.s.Males : No. (%) 15 (83) 71 (90) 429 (76) 166 (78) 115 (82) n.s. n.s.

Overall analyses were done excluding the normal control group (df¯ 3) and excluding the normal control group and TS withoutADHD groups (df¯ 2) using ANOVA or chi-square analyses.

groups remained matched for age, SES, and gendercomposition. Of children with Tourette’s syndrome withor without ADHD (N¯ 97), 82% (N¯ 80}97) hadcurrent tic symptoms (in the last month) and 18% (N¯17}97) tic symptoms were lifetime only. The average ageof onset of tics was 6±1 years old, and the mean durationof TS was 4±3 years, representing an average of 39% ofthe child’s life. The mean associated tic severity was 1±8(mild¯ 1, severe¯ 3) in the mild to moderate range.

Comparing the TS with ADHD group (N¯ 79) to theADHD alone group (N¯ 563), there were no meaningfuldifferences in the average age of onset of ADHD (3±6, 3±2years), its average associated impairment (moderate}severe), or the average duration of ADHD (7±3, 7±1years), respectively.

Omnibus analyses of the psychopathologic groupsrevealed significant overall differences in rates of mood,disruptive, anxiety, elimination, and psychotic disorders(see Table 2). These were primarily accounted for byhigher rates in the TS plus ADHD group and the ADHDgroup as compared to psychiatrically referred children.With few exceptions the rates of mood, disruptive,psychotic, and most anxiety disorders were statisticallyindistinguishable between the TS plus ADHD group andthe ADHD group. The exceptions were that rates ofobsessive compulsive disorder (OCD) and simple phobiawere higher in the TS plus ADHD group than in theADHD group. In addition, the TS minus ADHD grouphad a higher rate of OCD than the ADHD group and alower rate of oppositional defiant disorder (ODD) thanthe TS plus ADHD group. There were no meaningfuldifferences between the TS group and the ADHD groupin the ages of onset of any comorbid psychiatric disorders.

In order to examine comorbid pathology further wecreated a new variable. For this variable we summed thenumber of comorbidities beyond Tourette’s syndromeand ADHD; including depression, bipolar, conductdisorder, oppositional defiant disorder, multiple anxietydisorders, obsessive compulsive disorder, any eliminationdisorder, any language disorder, and psychosis (0¯none, 9¯highest). Ordinal logistic regression analysesrevealed that the TS plus ADHD group had a higheraverage number of additional comorbid disorders(2±9³1±9) than both the ADHD group (2±2³1±7) and theTS minus ADHD group (1±6³1±5; ps!±01).

Since the lifetime rate of psychosis was relatively highin the children with Tourette’s syndrome with andwithout ADHD, clinical records were examined. Psy-chotic symptoms were independently recorded in the

1040 T. SPENCER et al.

Table 2Rates of Psychiatric Diagnoses

TS minusADHD

TS plusADHD ADHD

Psychiatriccontrols

Normalcontrols

Significance(p)

(N¯ 18) (N¯ 79) (N¯ 563) (N¯ 212) (N¯ 140)χ# χ#

Diagnosis N % N % N % N % N % 3df 2df

Mood disordersMajor depression (severe) 1 6 23 29 147 26 35 18 2 1 ±04 n.s.Bipolar 1 6 15 19c** 78 14c** 8 4 0 0 ±0001 ±0001Dysthymia 3 17 9 11 51 9 18 9 1 1 n.s. n.s.

Disruptive disordersConduct disorder 2 11 16 20c* 109 19c** 18 8 4 3 ±002 ±001ODD 7 39a* 56 71c** 324 58c** 51 24 14 10 ±0001 ±0001ADD 0 0 79 100 563 100 0 0 0 0 n.a. n.a.

Anxiety disordersMultiple anxiety 7 39 33 42c** 168 30 44 21 6 4 ±002 ±001Separation anxiety 5 28 20 25 133 24 36 17 6 4 n.s. n.s.Overanxious 5 28 27 34c* 160 28c* 38 18 8 6 ±01 ±003Social phobia 1 6 14 18 81 14 23 11 4 3 n.s. n.s.Simple phobia 4 22 26 33bc** 81 14 22 10 8 6 ±0001 ±0001Agoraphobia 6 33c* 17 22c* 87 15 21 10 3 2 ±008 ±03Panic disorder 3 18 7 9 21 4 10 5 0 0 ±02 n.s.

OCD 5 28b**c* 16 21bc** 32 6 14 7 3 2 ±0001 ±0001

Elimination disordersEnuresis 2 11 28 35c* 153 27c* 38 18 16 11 ±004 ±003Encopresis 1 6 14 18 53 9 14 7 3 2 ±03 ±02

Language disordersLanguage 1 6 16 20 136 24 32 15 12 9 ±02 ±02Stuttering 0 0 8 10 29 5 8 4 5 4 n.s. n.s.

Psychosis 3 17c** 10 13c** 32 6c* 2 1 1 1 ±0001 ±0001

a vs. TS plus ADHD; b vs. ADHD; c vs. psychiatric controls.* p!±01; ** p!±001.Overall analyses and pairwise analyses were done excluding the normal control group (df¯ 3) and excluding the normal control

group and TS minus ADHD groups (df¯ 2) using chi-square analyses.

clinical charts in all patients. Of the 13 children, psychosiswas felt to be secondary to mood disorders in 60%, OCDin 20%, a primary diagnosis in 10%, and unknown in10%. Fifty per cent required neuroleptics to treat thepsychotic symptoms and another 25% were treated withneuroleptics for severe tics. Fifty per cent of children withTourette’s syndrome with psychotic symptoms had beenhospitalized.

Omnibus analyses of the psychopathologic groupsrevealed significant overall differences in rates of schooldysfunction but not of cognitive variables (WISC-R andWRAT subscales, and estimated Full Scale IQ). Thedifferences in school dysfunction were accounted for byhigher rates in the TS plus ADHD group and the ADHDgroup as compared to psychiatrically referred children.However, the TS plus ADHD group and the ADHDgroup did not differ from each other on any measures ofschool dysfunction or cognitive impairment (see Table 3).In contrast, the TS minus ADHD group had lower ratesof placement in special classes than the TS plus ADHDgroup. Similarly, omnibus analysis revealed significantoverall differences in psychosocial impairment (GAFscale) that were accounted for by lower function in the TSplus ADHD and the ADHD groups as compared topsychiatrically referred children. In addition, children inthe TS plus ADHD group were found to be more

psychosocially impaired than children in the ADHDgroup.

Further analyses of children with Tourette’s syndromewith or without ADHD (N¯ 97) were performed inorder to evaluate whether a differential pattern ofcomorbid disorders in children with Tourette’s syndromewould be associated with tic or ADHD associatedseverity. This analysis showed that rates of comorbiditydid not differ when stratified by the severity of ticsymptoms (mild [N¯ 43] vs. moderate}severe [N¯ 54],but did differ when stratified by the severity of ADHDsymptoms (none}mild}moderate [N¯ 40] vs. severe[N¯ 53]). Rates of major depression, bipolar disorder,conduct disorder, social phobia, and psychosis weresignificantly higher in children in the TS plus ADHDgroup who had more severe ADHD symptoms.

A similar analysis of measures of school dysfunctionand cognitive function revealed that with one exception(rates of special classes), these measures were not worse inchildren with Tourette’s syndrome with more impairingtics or more severe ADHD. Forty-nine per cent ofchildren with Tourette’s syndrome and severe ADHDwere enrolled in special classes compared to only 18%of children with Tourette’s syndrome and none}mild}moderate ADHD (p!±005). In children with Tourette’ssyndrome, the average level of psychosocial function was

1041DISENTANGLING THE OVERLAP BETWEEN TOURETTE’S DISORDER AND ADHD

Table 3Functional Characteristics of Sample

TS minusADHD(N¯ 18)

TS plusADHD(N¯ 79)

ADHD(N¯ 563)

Psychiatriccontrols

(N¯ 212)

Normalcontrols

(N¯ 140)Significance

(p)

N % N % N % N % N % 3df 2df

Repeated grade 4 22 17 22 120 21 29 14 18 11 n.s. ±05Placement in special classes 1 6a* 32 41c** 170 30c** 24 11 2 1 ±0001 ±0001Tutoring 8 44 45 57c** 322 58c** 73 35 37 23 ±0001 ±0001

Cognitive test M SD M SD M SD M SD M SD

SubscalesVocabulary 10 3±4 10±9 3±8 10±8 3±7 11±0 3±1 13±0 2±7 n.s. n.s.Block Design 11 2±5 11±7 3±6 11±7 3±8 12±3 3±4 14±9 3±3 n.s. n.s.Digit Span 9±4 2±6 8±6 3±6 9±0 3±4 9±4 3±0 10±8 2±8 n.s. n.s.Arithmetic 9±3 2±7 9±6 4±0 10±1 3±5 11±0 2±9 12±6 2±8 n.s. n.s.Digit Symbol 9±7 3±5 7±9 3±8 9±5 3±6 9±7 3±2 11±8 2±7 n.s. ±03WRAT Reading 88±2 33±8 89±4 33±6 86±6 36±7 83±0 42±5 102±3 11±3 n.s. n.s.WRAT Arithmetic 81±4 34±5 82±6 31±7 82±9 35±0 78±8 41±0 111±1 16±0 n.s. n.s.Estimated Full Scale IQ 101±3 15±3 97±8 31±2 104±5 18±1 107±8 12±2 117±9 10±3 n.s. ±04

GAF 52±2 7±1 47±3 7±3b*c** 50±0 7±8c** 56±3 9±8 68±7 9±4 ±0001 ±0001

a vs. TS plus ADHD; b vs. ADHD; c vs. psychiatric controls.* p!±01; ** p!±001.Overall analyses and pairwise analyses were done excluding the normal control group (df¯ 3) and excluding the normal control

group and TS minus ADHD groups (df¯ 2) using ANOVA and chi-square analyses.

unaffected by tic severity (Global Activity Scale [GAS]¯48, 48). In contrast, the severity of ADHD symptoms wasassociated with a significantly lower GAS score inchildren with Tourette’s syndrome (46 vs. 50±3; F¯ 8±34,p¯±005).

Discussion

In a systematic evaluation of correlates of Tourette’ssyndrome we found high rates of ADHD and obsessivecompulsive disorder (OCD) in these patients. However,in contrast to the comorbidity with OCD, other comor-bidities with disruptive behavior, mood and anxietydisorders, and neuropsychological deficits were indis-tinguishable in comparison between children withTourette’s syndrome and ADHD and children withADHD alone. These results support the specificity of theassociation between Tourette’s syndrome and OCD butsuggests that many other psychiatric and cognitiveimpairments associated with this disorder could besecondary to the comorbidity with ADHD. However, ourfindings also show that childrenwithTourette’s syndromeplus ADHD have lower psychosocial function thanchildren with ADHD alone.

Our findings documenting high rates of comorbiditywith ADHD in patients with Tourette’s syndrome arealso highly consistent with an extensive Tourette’s syn-drome literature. The reported rate of comorbid ADHDin Tourette’s syndrome patients has ranged from 35 to90% in different studies (average 52%; N¯ 20 studies ;" 2000 subjects) (Bruun, 1984; Comings, 1995; Comings& Comings, 1985, 1987b, 1990; Erenberg et al., 1986;Erenberg & Rothner, 1978; Fernando, 1967; Jagger etal., 1982; Moldofsky et al., 1974; Pauls et al., 1993, 1996;Shapiro et al., 1978, 1988; Singer & Rosenberg, 1988;

Spencer et al., 1995; Stefl, 1984; Stokes et al., 1995; Sverdet al., 1988; Wilson et al., 1982). Comings and Comingssuggested that comorbid ADHD represents a geneticvariant of Tourette’s syndrome (Comings, 1995;Comings & Comings, 1990), whereas Pauls et al. (1993)proposed that Tourette’s syndrome and ADHD may beetiologically related in some individuals. Irrespective ofthe uncertain etiologic association between ADHD andTourette’s syndrome, little doubt remains that ADHD ishighly prevalent in patients with Tourette’s syndromeand often represents the main clinical concern and theprincipal source of dysfunction and disability.

Our findings documenting the specificity of the as-sociation between Tourette’s syndrome and OCD arealso highly consistent with the literature (Comings &Comings, 1987e; Pauls, 1992a; Pauls, Alsobrook, Good-man, Rasmussen, & Leckman, 1995). High levels ofcomorbidity between Tourette’s syndrome and OCDhave been reported both in studies of Tourette’s syn-drome and studies of OCD patients (Pauls, 1992b; Paulset al., 1995). These findings are consistent with evidencefrom family genetic studies, suggesting that OCD andTourette’s syndrome may represent variable expressionsof a common underlying risk factor (Pauls, 1992a; Paulset al., 1995).

However, in contrast to the specificity of the associ-ation between Tourette’s syndrome and OCD, othercomorbidities and neuropsychological deficits did notdiffer between Tourette’s syndrome and ADHDpatients. Although the literature on Tourette’s syndromehas consistently identified high levels of comorbidity withdisruptive, mood, and anxiety disorders in patients withTourette’s syndrome (Comings, 1995; Comings &Comings, 1987a, b, c, d, e, f ; Erenberg et al., 1987; Paulset al., 1993, 1994; Riddle, Hardin, Ort, Leckman, &

1042 T. SPENCER et al.

Cohen, 1988; Robertson et al., 1988; Stefl, 1984), theseresults suggest that these comorbidities and cognitivedeficits could be accounted for by the comorbidity withADHD and may not represent specific correlates of TS.

Supporting the notion that comorbiditywith disruptivemood and anxiety disorders as well as school andcognitive deficits in patients with Tourette’s syndromeare due to ADHD are results reported by Comings et al.in a series of studies comparing findings between indi-viduals with Tourette’s syndrome with and withoutADHD (Comings, 1995; Comings & Comings, 1987a, b,c, d, e). These investigators found that individuals withTourette’s syndrome and ADHD had higher rates ofcomorbid psychiatric and learning disorders as well ashigher rates of treatment and hospitalization than didindividuals with Tourette’s syndrome without ADHD.

Although the lifetime rate of psychosis was relativelyhigh in the children with Tourette’s syndrome, a furtherreview of clinical records corroborated the presence ofpsychotic symptoms. Rates of neuroleptic use and hos-pitalization provide further evidence of the severity ofthese complex cases. In addition, there were few controlchildren diagnosed with psychosis (1%). It is not sur-prising to see increased rates of psychosis in the presenceof mood disorders, especially childhood mania (Ker-beshian et al., 1995; Strober & Carlson, 1982; Wozniak etal., 1995). Others may not have found psychosis in thispopulation because neuroleptics used for tics may havemasked psychotic features. Although the literature issparse, there is a published report of a similar phenomena.Comings and Comings (1987e) reported similar rates ofpsychotic symptoms in patients with Tourette’s syndromeas well as low rates in both ADHD patients and controls.In their study, psychotic symptoms included auditoryhallucinations ‘‘voices were often blamed for telling themto do bad things and were frequently identified with thedevil ’’ (Tourette’s syndrome [15%] vs. ADHD [0%] vs.controls [2%]) as well as paranoid thoughts ‘‘someone isplotting against or trying to hurt or poison one’’(Tourette’s syndrome [11%] vs. ADHD [0%] vs. controls[0%]). Since this finding is relatively novel, replicationfrom additional investigators will be important to es-tablish the magnitude of this issue in Tourette’s syn-drome.

The findings presented in this report should beevaluated in light of their methodological limitations. Wehave already reported that Tourette’s syndrome andchronic tic disorders were part of the same disorder, withTourette’s syndrome being a more severe form of ticdisorder (Spencer, Biederman, Harding, Wilens, &Faraone, 1995). While we would expect similar findingsin this study, in this report we did not include chronic ticdisorders. The diagnosis of Tourette’s syndrome wasderived from semistructured diagnostic interviews withthe mothers and not by direct examinations of thechildren. Although this approach may have under-estimated the true rate of tics in our study sample, thiswould not change the results. Moreover, considering thewaxing and waning profile of Tourette’s syndrome andthe ability of individuals to inhibit tics, as well as thelimited ability of children to report precisely on theirprior history of tics, parental interviews may be quiteinformative in assessing tic disorders in children (Leck-

man, Walker, & Cohen, 1993; Schwab-Stone, Fallon,Briggs, & Crowther, 1994).

It is possible that the relatively limited set of questionsabout tics in this interview could have lead to under- orover-endorsing children’s symptoms. In this study, we didnot use detailed tic rating scales that assess individualqualities such as the number, frequency, intensity, andcomplexity of tics. The use of such scales would not havechanged our results on the overall effect of chronicTourette’s ; nevertheless, future studies may benefit fromdirect examination of the children and the use of moredetailed tic rating scales. Also, since our Tourette’ssyndrome sample was ascertained from a pediatricpsychopharmacology clinic, our results may not gene-ralize to community samples. Thus, more work is neededin further evaluation of these neuropsychiatric correlatesof children with Tourette’s syndrome in communitysamples.

It is possible that observed similarities between TS andADHD groups in our study may have been due toascertainment of the sample, since referral may have beenfor behavioral or psychiatric problems and not ticsymptoms per se. However, a recent study at our centerfound that ‘‘undeclared’’ Tourette’s patients referred tothe general pediatric psychopharmacology clinic shareessentially the same phenotypic, sociodemographic, andclinical correlates, including patterns of Axis I comor-bidity, as ‘‘declared’’ Tourette’s patients referred to thespecialized Tourette’s syndrome clinic. (Coffey et al.,1997).

A further limitation of this investigation is the smallsize of childrenwithTourette’s syndromewithout ADHD(N¯ 18). The smallness of this subgroup is a finding in itsown right ; few children with Tourette’s syndrome with-out ADHD were referred for psychiatric evaluation.Further, though children in this subgroup did not meetfull criteria for ADHD, most had some symptoms ofADHD. Thus low power and the presence of sub-threshold ADHD restricted our ability to make a fullcomparison to a TS without ADHD group. Nevertheless,children with Tourette’s syndrome without full ADHD inour sample displayed relatively high rates of OCD andselected anxiety disorders and lower rates (mostly trends)of mood, disruptive, elimination, and language disordersas well as less (mostly trends) school, cognitive, andpsychosocial dysfunction. Despite the low power andpresence of some ADHD in this group, these findings areof interest to generate hypotheses for future study.Although these findings are supportive of the currentstudy hypotheses, our conclusions do not rest on these 18subjects.

Despite these limitations, our findings from a largepopulation of referred youth indicate that comorbiditywith disruptive behavioral, mood, and anxiety disordersas well as cognitive dysfunction previously associatedwith Tourette’s syndrome may be secondary to thecomorbidity with ADHD. In contrast, association withobsessive compulsive disorder appears to be Tourette’ssyndrome specific.

Acknowledgements—Preparation of this article was sup-ported in part by a grant from the Tourette Society Associationand NIMH grant K20 MH01169-01 (Dr Spencer).

1043DISENTANGLING THE OVERLAP BETWEEN TOURETTE’S DISORDER AND ADHD

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Manuscript accepted 7 January 1998