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ADHD symptom presentation and trajectory in adultswith borderline and mild intellectual disabilityjir_1270 668..677

K. Xenitidis,1 E. Paliokosta,2 E. Rose,3 S. Maltezos1 & J. Bramham4

1 South London and The Department of Maudsley Foundation Trust, Adult ADHD Service, London, UK2 Institute of Psychiatry, Child and Adolescent Psychiatry, London, UK3 University of Hertfordshire, Hatfield, UK4 University College Dublin, UCD School of Psychology, Dublin, Ireland

Abstract

Background This study examined symptoms andlifetime course of Attention Deficit HyperactivityDisorder (ADHD) in adults with borderline andmild Intellectual Disability (ID).Method A total of 48 adults with ID and ADHDwere compared with 221 adults with ADHDwithout ID using the informant Barkley scale forchildhood and adulthood symptoms.Results The ADHD/ID group presented withgreater severity of (adult and childhood) symptomscompared with the non-ID group. For the ADHD/non-ID group, most symptoms improved signifi-cantly from childhood to adulthood, whereas onlytwo symptoms changed significantly for the IDgroup. Principal component analysis revealed scat-tered loading of different items into five compo-nents for the ADHD/ID group that were notconsistent with the classic clusters of inattentive,hyperactive and impulsive symptoms. A negativecorrelation was found between severity of symptomsand IQ.

Conclusions ADHD in adults with ID may have amore severe presentation and an uneven and lessfavourable pattern of improvement across thelifespan in comparison with adults without ID.

Keywords adults, Attention Deficit HyperactivityDisorder, ID, symptoms profile

Introduction

Attention Deficit Hyperactivity Disorder (ADHD)is a common neurodevelopmental disorder causingsignificant distress and impairment. (Faraone et al.2000) DSM-IV diagnostic criteria require at leastsix symptoms in each domain of inattention andhyperactivity/impulsivity for the combined type tobe diagnosed or symptoms in one domain for theinattentive or hyperactive type, respectively. ICD-10

classification of hyperkinetic disorder correspondsto the DSM-IV criteria of the combined type.ADHD diagnostic validity for adults has been onlyrecently established. (Toone 2004; Zwi & York2004) Comorbidity is the norm rather than theexception (Kutcher et al. 2004), and this often com-plicates the diagnostic process and affects treat-ment. More specifically, the coexistence of

Correspondence: Dr Elena Paliokosta, Institute of Psychiatry,Department of Child and Adolescent Psychiatry, London, UK(e-mail: [email protected]).

Journal of Intellectual Disability Research doi: 10.1111/j.1365-2788.2010.01270.x

volume 54 part 7 pp 668–677 july 2010668

© 2010 The Authors. Journal Compilation © 2010 Blackwell Publishing Ltd

hyperactivity and ID has long been noted but thevalidity of the diagnosis of ADHD in people withID has recently attracted attention (Antshel et al.2006). However, studies have shown a higherprevalence (Dekker & Koot 2003) and a worseprospective outcome of ADHD in children andadults with ID (Lambert et al. 1987; Peterson et al.2001).

‘Diagnostic overshadowing’ may lead to the attri-bution of hyperactive, impulsive and inattentivesymptoms to the ID itself and thus obscure theidentification of ADHD in this population (Reiss &Szyszko 1983) as clinical presentation of ADHD inthis group is not well established. (Sevin et al. 2003)Additionally, clinicians feel more confident aboutmaking a diagnosis of ADHD in patients withoutID (Jopp & Keys 2001; Gillberg et al. 2004) ratherthan in those with ID. This could be also due to adifficulty in establishing whether activity and atten-tion levels are consistent or not with the develop-mental stage of the individual with ID as DSM-IVcriteria indicate.

The phenomenology of ADHD and ID has beenstudied much more in children and adolescents.Although the presentation of mental disorders inpeople with ID is often atypical, there is evidencethat children with ID and ADHD exhibit classicalsymptoms of ADHD such as poor selective atten-tion (Pearson et al. 1996), off-task behaviour andfidgeting compared with their ID peers who don’tpresent with ADHD symptoms. (Handen et al.1998) Ishii et al. (Ishii et al. 2003) found no statisti-cally significant difference in the presentation ofDSM-IV symptoms of ADHD in children with IDcompared with children of normal intelligence.Using observational measures, Fee et al. (Fee et al.1994) also concluded that children with ID andADHD show a pattern of ADHD symptoms similarto that of normal intelligence children diagnosedwith ADHD. Simonoff et al. (Simonoff et al. 2007)found a negative linear relationship between ADHDsymptoms and IQ (beta = -0.087, P < 0.001) inadolescents with mild ID. Neither the profiles ofADHD symptoms nor the comorbidity withemotional/behavioural problems differed accordingto the presence of ID. These findings suggest thatthe clinical presentation of ADHD is similar acrossindividuals with different intellectual levels inchildhood.

However, it is not clear whether these observa-tions also apply to adults with ADHD and ID andwhether the symptoms improve from childhood toadulthood as it is the case for non-ID individualswith ADHD. Adults with ADHD and mild or bor-derline ID assessed by our team at the AdultADHD Service at the Maudsley Hospital werefound to be significantly more impaired in terms ofselective attention and response inhibition com-pared with adults with ADHD and normal cogni-tive function during neuropsychological assessment(Rose et al. 2009). The present study aims todescribe the clinical presentation and course ofADHD in adults with ID and compare ADHDsymptomatology in adults with and without ID. Thefollowing research questions were addressed:1 What is the ADHD presentation of adults withID? Based on the neuropsychological findings men-tioned above we hypothesised that adults with IDwould present with increased severity of their symp-toms compared with non-ID adults.2 Is the symptom trajectory from childhood intoadulthood different for the two groups?3 Do the symptoms in the ID group co-occur inthe same pattern as in the non-ID group?4 Finally, how do symptoms correlate to IQ?

Method

Design

This study was a retrospective study based on thecopies of Barkley Scales (informant version)(Conners & Barkley 1985) for adulthood and child-hood symptoms found within the medical caserecords of adults who received clinical assessmentsfor ADHD in a specialist outpatient clinic.

Setting

The study was conducted at the Adult ADHDService at the Maudsley Hospital, London. This is aSpecialist Service established in 1994 providingdiagnostic assessments and treatment for adultswith ADHD from throughout the UK.

Sample

The sampling frame of the present study consistedof all adults who attended the clinic between 2001

669Journal of Intellectual Disability Research volume 54 part 7 july 2010

K. Xenitidis et al. • ADHD in adults with intellectual disability


and 2006. All patients diagnosed with ADHD(n = 269) who had completed neuropsychologicalassessment and provided informant rating scaleswere included in the sample. Of those, 48 patientswere found to have IQ equal to or below 80

and were defined as the ‘ADHD/ID’ group, while221 patients with IQ above 80 were the ‘ADHD/non-ID’ group. We decided to include people in the‘borderline’ (IQ between 70 and 80) range of intel-lectual functioning in the ‘ADHD/ID groupbecause of the similarities in the relevant manage-ment issues. Additionally, because the number ofthe patients in the ID group was relatively small itwas not possible to conduct separate analysis forthe borderline intelligence group. All patients wereattending the clinic for assessment of their currentADHD symptoms. 52% of the ID group and 42%of the non-ID group had a previous diagnosis andhad received some treatment in the past for the dis-order; however, the exact treatment regimens foreach patient were not available.

Measures of ADHD symptoms

Given that ADHD is a neurodevelopmental disor-der, it is necessary to establish that symptoms werepresent in childhood. Pre-assessment questionnaireswere posted to each patient referred, in order toobtain preliminary data about ADHD symptoms inchildhood and adulthood. These include theBarkley Scales (patient and informant version)(Barkley & Murphy 1998; Conners & Barkley 1985)for adulthood and childhood symptoms. This scalecontains the 18-symptom items for ADHD fromDSM-IV-TR that are scored from 0 (never orrarely) to 3 (very often) and a total score derivedfrom adding symptom scores. All data analyses wereconducted based on informant-rating scales. Thereason for choosing informant vs. self-report scaleswas the fact that the latter were missing or incom-plete in a significant proportion of patients with IDbut also because diagnosis during childhood isbased traditionally on parents/informant reportsabout hyperactivity.

A comprehensive neuropsychological evaluationwas conducted at the time of assessment includingthe Wechsler Adult Intelligence Scale-III (Wechsler1997) or the Wechsler Abbreviated Intelligence

Scale. (Wechsler 1999) A DSM-IV diagnosis ofADHD was assigned by experienced clinicians.

Statistical analysis

We conducted Kolmogorov–Smirnov test to checkour measures regarding normal distribution. Asresults were consistent with non-normal distributionfor item scores although distribution was normal fortotal scores, non-parametric tests, Mann–Whitney,were conducted to compare total Barkley score aswell as each item score for the ID and non-IDgroup. Subsequently, we conducted Wilconxonsigned ranks test, a non-parametric test, withingroups to compare adulthood vs. childhood symp-toms scores in order to examine different course inthe symptomatology between the ID and the non-IDgroup.We further conducted a principal componentanalysis of Barkley scale to investigate different pat-terns of loading of items. A rotated componentmatrix was produced using Varimax method withKaiser Normalization. Finally, we correlated itemsscores with IQ score. Significance level for all testswas set at P < 0.05. All analyses were conductedusing spss statistical package. (Field 2005)

Results

The ADHD/ID group consisted of 34 men and 14

women, while the ADHD/non-ID group of 140

men and 81 women. The ADHD/ID group (n = 48)had a mean age of 24.63 years (range 16–43,SD = 7.394) and mean IQ of 70.27 (range 52–80,SD = 8.115). The ADHD/non-ID group (n = 221)had a mean age of 29.31 years (range 17–57,SD = 8.908) and mean IQ 106.27 (range 81–145,SD = 14.295). There was no significant differencefor age and sex distribution between the twogroups. Cronbach’s alpha for our data is 0.878,which shows high internal reliability. Kolmogorov–Smirnov z-test was significant for all symptomsitems except the Current Barkley total score sonon-parametric tests were conducted.

Symptom severity: comparison of ADHD/ID groupwith ADHD/non-ID group

Adulthood symptoms

Total Barkley score in adulthood was used as anindicator of symptom severity for ADHD/ID group




compared with ADHD/non-ID group. There was astatistically significant difference with ADHD/IDgroup scoring higher compared with ADHD/non-ID group. Results are presented in Table 1.ADHD/ID group had also higher scores in allBarkley items. In five out of nine inattentive itemsand in four out of nine hyperactivity/impulsivityitems these differences were statistically significant.

Childhood symptoms

Similarly, ADHD/ID group presented a statisticallysignificant higher total Barkley score in childhood.As indicated in Table 1, this group differed signifi-cantly from the non-ID group in eight out of nineinattentive and six out of nine hyperactivity/impulsivity symptoms.

Symptoms within trajectory: group comparisonbetween childhood and adulthood scores

Within each group, paired samples statistics wereconducted for each item comparing childhood andadulthood scores in order to assess the lifetimecourse of the disorder. For the ADHD/non-IDgroup there was significant decrease in ratingsindicative of improvement over time. This was thecase for the total score of Barkley scale as well asfor almost all symptom items in both domains ofinattention and hyperactivity/impulsivity (Table 1).This is a biopsychological pattern consistent withthe general notion that ADHD symptoms tend toimprove with (brain and psychosocial) maturation.For the ADHD/ID group, although there was anoverall decrease in scores, there were significant dif-ferences only for two inattentive and two hyperac-tive items and the total score.

Symptoms pattern: clustering of symptoms in theADHD/ID and the ADHD/non-ID group

Symptoms principal component analysis for adult-hood symptoms revealed that three components forthe ADHD/non-ID group accounted for 64.26% ofthe variance for ratings. All the inattentive symp-toms loaded for the first component and all threeimpulsivity items (blurting out answers, difficultywaiting turn and interrupting) and one hyperactivity

item (talking excessively) loaded for the secondcomponent. Hyperactivity symptoms loaded for thethird component.

For the ADHD/ID group, five components wereidentified with scattered loading of different itemsto account for 73.98% of the variance for ratings.The first component included the three impulsivitysymptoms (blurting out answers, difficulty waitingturn and interrupting) and one hyperactivity item(talking excessively) suggesting that these symptomscould represent a discrete cluster of difficulties forthe adult ADHD/ID patients. However, the othercomponents did not follow any particular patternwith only four inattentive symptoms (organisationproblems, avoiding mental effort, losing things andforgetting) loading with one hyperactive symptomin component 2.

Correlation of symptoms withintellectual functioning

Pearson’s product moment correlations between IQand Barkley’s total score in adulthood were con-ducted and showed a negative correlation betweenscores and IQ (-4.15, P < 0.001). A negative corre-lation was also found for each Barkley’s item sepa-rately. This means that the lower the IQ the higherthe Barkley scores and this was the case when eachgroup was analysed separately and when the wholesample was analysed altogether.

Discussion

Our results indicate that the clinical presentation ofADHD in adults with ID has certain differenceswhen compared with non-ID adults with ADHD.Mean total score on Barkley scale was significantlyhigher in adulthood for the ADHD/ID group indi-cating greater severity. This difference was evenmore pronounced for childhood total score. Addi-tionally, both inattentive and hyperactivity/impulsiveitems on Barkley scale were higher rated for theADHD/ID group.

It could be argued that higher scores for ADHDsymptoms in children and adults with ADHD/IDoccurred simply as a by-product of ID. However,there is evidence from literature that deficits exhib-ited by children with ADHD/ID are different from




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those of children with ID without ADHD. (Handenet al. 1998; Pearson et al. 2000) Data from ourservice, analysing neuropsychological findings inADHD/ID patients compared with ADHD/non-IDshowed greater deficits in attentional and responseinhibition functioning, observe that remained sig-nificant when the analysis specifically controlled forthe contribution of intelligence. (Rose et al. 2009)These studies and present results support thenotion that individuals with ADHD and ID face a‘double vulnerability’ in terms of attention andbehaviour inhibition, because they experience boththe deficits imposed by ADHD and those associatedwith ID.

This finding could carry some interesting clinicalimplications. Not only ADHD is underdiagnosed inchildren and adults with ID as discussed in theintroduction, but also it is related with moreimpairment. Taken into account that they representa vulnerable group with increased needs for clinicaland living support, identification of the ADHDcontribution to the overall impairment could beimportant as ADHD symptoms can be managedboth with pharmacological and non-pharmacological treatments, leading to everyday lifeimprovement.

With regards to change of symptoms over time,the ADHD/ID group did not achieve significantimprovement in most of their symptoms from child-hood to adulthood while the ADHD/non-IDgroup’s scores decreased significantly for the major-ity of items including the total score. This couldmean that not only do people with ID have moresevere symptoms but also these symptoms show alower tendency to improve over time compared withnon-ID peers. It should be noted that only oneitem, ‘restlessness’, was shown to deteriorate fromchildhood to adulthood for both the ID and thenon-ID group. This item can be interpreted asmotor overactivity but also as anxiety, and thereforeit could reflect secondary anxiety that is moreintense during adulthood as a result of heightenedsymptoms’ awareness and increased life demands.

The finding that people with ID have as a groupa poorer prognosis of the ADHD can be explainedin different ways. They are reported to have apoorer prognosis when they present with mentalhealth problems in general. (Tonge & Einfeld 2000)In the case of ADHD, people with ID may present

decreased ability to develop copying strategiesbecause of their cognitive deficits so ADHD symp-toms may manifest more severely and persistlonger. This is consistent with follow-up medicationstudies that concluded that ADHD persistence intoadulthood is related with IQ in people with ID.(Lambert et al. 1987; Peterson et al. 2001). Otherstudies regarding medication treatment of ADHD,demonstrated that children with ADHD and IDhave similar, if not increased, risk for persistence ofADHD from childhood into adolescence (Amanet al. 1993) while they were more likely to demon-strate significant behavioural difficulties in adoles-cence (Aman et al. 1996). On the other hand little isknown about the response of people with ID toADHD pharmacotherapy as randomised controlledtrials are sparse in this population. However, thisstudy was not designed to assess the effect of treat-ment. Therefore, we cannot conclude to what extentthe poor outcome in the ADHD/ID group wasrelated to poor treatment response (including phar-macological and psychological) or whether itreflects an underlying maturational delay. Prospec-tive studies investigating the long-term course andimpact of ADHD in children with ID along withresponse to interventions will possible replicate andprovide further information about this finding.

The principal component analysis showed thatsymptoms clustered differently for the ADHD/IDgroup in comparison to the ADHD/non-ID. Thisfinding suggests that ADHD profile in ID people isnot similar with the general population profile,indicative of atypical presentation. Impulsive symp-toms represented a clear component for the IDgroup and four inattentive symptoms loaded tocomponent 2 but the other symptoms loaded in ascattered way to the other three components(Table 2). In contrast, the component analysis forthe ADHD/non-ID group, revealed loading ofsymptoms to three factors representing the threecore dimensions of the clinical presentation: inatten-tion, hyperactivity and impulsivity with item ‘talkingexcessively’ loading on impulsivity rather thanhyperactivity component. There is a generallyaccepted view that mental health disorders mayhave an atypical clinical presentation in ID patients.A recent British study indicated that prevalence, sexdistribution and presentation of comorbid psychiat-ric disorders may differ in patients with ID from




those of the general population. (Bhaumik et al.2008) However, in that study, ADHD diagnosis wasnot considered for any patient although a significantproportion of patients did present with behaviouralproblems. ADHD presentation in adults with IDremains thus an area with little empirical data avail-able. Our results should be considered preliminaryparticularly because our sample was overrepre-sented by mild and borderline ID patients.

The finding of a negative correlation of IQ withBarkley’s scores along the intellectual ability rangeindicates that the negative correlation of ADHDsymptoms with IQ identified for children (Simonoffet al. 2007) is the case for adults as well. Such afinding indicates that ADHD should be morecommon in people with lower IQ. Adults with mod-erate and severe ID would thus be benefited froman assessment for ADHD when they present withsymptoms along the lines of inattention and behav-ioural inhibition. This is particularly importanttaking into account the lack of confidence of clini-cians making an ADHD diagnosis in the ID popu-lation. Because clinicians have identified theirdifficulty to interpret meaningfully DSM-IV state-

ment that ADHD symptoms should be develop-mentally inappropriate in ID patient, if ADHD ismore common in the ID population further trainingin the area and assessments conducted in special-ised settings is probably required for the efficientmanagement of this population. This would be alsoconsistent with NICE guidelines that recommendthat assessment of ADHD is conducted by special-ised services irrespective of possible comorbidity.

Although it is unlikely that the debate about thevalidity of ADHD diagnosis in adults and particu-larly those with ID will be resolved in the nearfuture, it is important to emphasise the fact that theseverity of symptoms may have important clinicalimplications for response to treatment and outcomein terms of functioning. From a clinical perspective,early and accurate differential diagnosis and inter-vention may have a profound impact on the level ofimpairment. In order to make a careful diagnosis ofADHD it is necessary that scores on standardisedmeasures, informant-rating scales, clinical impres-sions and psychological testing are obtained. Ourstudy provides preliminary data about the presenta-tion and the course of ADHD in this group of

Table 2 Factor pattern for principal component analysis for the ADHD/ID group

ADHD/non-ID group ADHD/ID group

F1 F2 F3 F1 F2 F3 F4 F5

Making careless mistakes 0.736 0.843Short attention span 0.687 0.446 0.733Doesn’t listen when spoken directly 0.572 0.442 0.481 0.522Difficulty with following instructions and completing tasks 0.808 0.814Organisation difficulties 0.743 0.787Avoiding mental effort 0.716 0.461 0.531Losing things 0.786 0.760Distractibility 0.717 0.816Forgetting 0.757 0.910Fidgeting 0.738 0.742Leaving seat 0.698 0.734Restlessness 0.705 0.884Being loud 0.458 0.431 0.448Being always on the go 0.674 0.401 0.421Talking excessively 0.711 0.889Blurting out answers 0.819 0.744Difficulty waiting turn 0.740 0.744Interrupting 0.808 0.858

ADHD, Attention Deficit Hyperactivity Disorder.




patients, using instruments based on DSM-IVdiagnosis.

Our study has some limitations that should betaken into consideration before generalising theresults. The first issue relates to the validity of thedefinition of ID used. Participants with ADHDwere assigned to the non-ID and ID group basedon their scores obtained from tests of overall intel-lectual functioning using a short form of the Wech-sler Adult Intelligence Scale-III or the WechslerAbbreviated Intelligence Scale. However, we did nothave information about everyday functioning that isrequired in order to assign formally the diagnosis ofID. Moreover, the commonly accepted IQ cut-off of70 was expanded to 80 as this ‘borderline intelli-gence’ subgroup often presents with similar educa-tional, social and occupational mild impairment(and thus management issues) as the ID group.

The second limitation concerns the validity of theBarkley Scale for assessing ADHD symptoms. Alldata analysed were collected in the context of anoutpatient service. We chose to include only infor-mant data as ID patients’ rating scales were missingor inadequately completed in a substantial propor-tion of the cases. Parent reports and scores are acommon strategy to collect information aboutbehavioural disorders in children that is consideredreliable. (Faraone et al. 1995) However, recall biascould represent a problem for our study as it is awell-known research limitation in this type ofstudies. Because the concept of ADHD in adult-hood has only recently been established, cross-sectional studies collecting retrospectively childhooddata is a useful way to provide some preliminaryresults that will direct future research strategies forprospective research. Manuzza et al. (Mannuzzaet al. 2002) reported a satisfactory correlation ofretrospective symptoms’ recall of adults diagnosedwith ADHD as children with the symptomsrecorded in past clinical notes. Another study(Kooij et al. 2008) compared different measures andconcluded that adults were the best informant fortheir own symptoms, underestimated though sever-ity. Other studies have challenged though the speci-ficity of retrospective self-reports of childhoodADHD symptoms (Loney et al. 2007; Suhr et al.2009). Use of both self-reports and parental reportsto assess past ADHD symptoms is a practice usedand their agreement has been estimated as moder-

ate. (Dias et al. 2008) However, the few existingstudies about validity of retrospective symptoms’accounts have not included ID patients.

Another limitation of the study is that onlypatients diagnosed with ADHD were included, asthere were too few ID patients not diagnosed withADHD to be included for comparison. Some ofthese patients have been diagnosed in childhoodwith ADHD but not for all of them informationregarding assessment and treatment was available.Furthermore, ID patients referred and includedwere in the range of borderline to moderate IDrange. This probably reflects the long-standingbelief of clinicians that ADHD symptoms representinnate difficulties for ID patients, especially in themore severe range and does not warrant a comorbiddiagnosis of ADHD, particularly in the context of areferral to a National Service.

Conclusions

Accurate empirically based description of ADHDsymptoms in the adult ID population is importantfor improved recognition and appropriate treatmentof the condition. Our findings indicate that ADHDin adults with ID may have a more severe andatypical presentation and an uneven and lessfavourable pattern of improvement across thelifespan in comparison with adults without ID. Cli-nicians should include investigation of ADHD-related symptoms in their routine assessment of IDpatients, particularly because ADHD is a treatablecondition, which otherwise can impair further theireveryday life functioning both in terms of academicand occupational functioning and affect their abilityfor independent living in the community.

Declarations of interest

None of the authors has any interest to declare.

References

Aman M. G., Kern R. A., McGhee D. E. & Arnold L. E.(1993) Fenfluramine and methylphenidate in childrenwith mental retardation and attention deficit hyperactiv-ity disorder: laboratory effects. Journal of Autism andDevelopmental Disorders 23, 491–506.




Aman M. G., Pejeau C., Osborne P., Rojahn J. & HandenB. (1996) Four-year follow-up of children with lowintelligence and ADHD. Research in Developmental Dis-abilities 17, 417–32.

Antshel K. M., Phillips M. H., Gordon M., Barkley R. &Faraone S. V. (2006) Is ADHD a valid disorder in chil-dren with intellectual delays? Clinical Psychology Review26, 555–72.

Barkley R. A. & Murphy K. R. (1998) Attention-DeficitHyperactivity Disorder: A ClinicalWorkbook. The GuilfordPress, New York.

Bhaumik S., Tyrer F. C., McGrother C. & GanghadaranS. K. (2008) Psychiatric service use and psychiatric dis-orders in adults with intellectual disability. Journal ofIntellectual Disability Research 52, 986–95.

Conners C. K. & Barkley R. A. (1985) Rating scales andchecklists for child psychopharmacology. Psychopharma-cology Bulletin 21, 809–43.

Dekker M. C. & Koot H. M. (2003) DSM-IV disorders inchildren with borderline to moderate intellectual disabil-ity. I: prevalence and impact. Journal of the AmericanAcademy of Child and Adolescent Psychiatry 42, 916–22.

Dias G., Mattos P., Coutinho G., Segenreich D., SaboyaE. & Ayrao V. (2008) Agreement rates between parentand self-report on past ADHD symptoms in an adultclinical sample. Journal of Attention Disorders 12, 70–5.

Faraone S. V., Biederman J. & Milberger S. (1995) Howreliable are maternal reports of their children’s psycho-pathology? One-year recall of psychiatric diagnoses ofADHD children. Journal of the American Academy ofChild and Adolescent Psychiatry 34, 1001–8.

Faraone S. V., Biederman J., Spencer T., Wilens T.,Seidman L. J., Mick E. et al. (2000) Attention-deficit/hyperactivity disorder in adults: an overview. BiologicalPsychiatry 48, 9–20.

Fee V. E., Matson J. L. & Benavidez D. A. (1994) Atten-tion deficit-hyperactivity disorder among mentallyretarded children. Research in Developmental Disabilities15, 67–79.

Field A. (2005) Discovering Statistics Using SPSS, (Trans).SAGE publications Ltd, London.

Gillberg C., Gilberg I. C., Rasmussen P., Kadesjiö B.,Söderström H., Råstam M. et al. (2004) Co-existingdisorders in ADHD – implications for diagnosis andintervention. European Child & Adolescent Psychiatry 13,180–92.

Handen B., McAuliffe S., Janosky J., Feldman H. &Breaux A. M. (1998) A playroom observation procedureto assess children with mental retardation and ADHD.Journal of Abnormal Child Psychology 26, 269–77.

Ishii T., Takahashi O., Kawamura Y. & Ohta T. (2003)Comorbidity in attention deficit–hyperactivity disorder.Psychiatry and Clinical Neurosciences 57, 457–63.

Jopp D. A. & Keys C. B. (2001) Diagnostic overshadowingreviewed and reconsidered. American Journal of MentalRetardation 106, 416–33.

Kooij S. J., Boonstra M. A., Swinkels S. H. N., BekkerE. M., de Noord I. & Buitelaar J. K. (2008) Reliability,validity, and utility of instruments for self-report andinformant report concerning symptoms of ADHD inadult patients. Journal of Attention Disorders 11, 445–58.

Kutcher S., Aman M., Brooks S., Buitelaar J., van DaalenE., Fegert J. et al. (2004) International Consensus state-ment on attention-deficit/hyperactivity disorder(ADHD) and disruptive behaviour disorders (DBDs):clinical implications and treatment practice suggestions.European Neuropsychopharmacology 14, 11–28.

Lambert N. M., Hartsough C. S., Sassone D. & SandovalJ. (1987) Persistence of hyperactivity symptoms fromchildhood to adolescence and associated outcomes. TheAmerican Journal of Orthopsychiatry 57, 22–32.

Loney J., Ledolter J., Kramer J. R. & Volpe R. J. (2007)Retrospective ratings of ADHD symptoms made atyoung adulthood by clinic-referred boys with ADHD-related problems, their brothers without ADHD, andcontrol participants. Psychological Assessment 19, 269–80.

Mannuzza S., Klein R. G., Klein D. F., Bessler A. &Shrout P. (2002) Accuracy of adult recall of childhoodattention deficit hyperactivity disorder. The AmericanJournal of Psychiatry 159, 1882–8.

Pearson D. A., Yaffee L. S., Loveland K. A. & Lewis K. R.(1996) Sustained and selective attention in children withmental retardation: a comparison of children with andwithout ADHD. American Journal on Mental Retardation100, 592–607.

Pearson D. A., Lahar D., Loveland K. A., Santos C. W.,Faria L. P., Azzam P. N. et al. (2000) Patterns of behav-ioral adjustment and maladjustment in mental retarda-tion: comparison of children with and withput ADHD.American Journal of Mental Retardation 105, 236–51.

Peterson B. S., Pine D. S., Cohen P. & Brook J. S. (2001)Prospective, longitudinal study of tic, obsessive-compulsive, and attention-deficit/hyperactivity disordersin an epidemiological sample. Journal of the AmericanAcademy of Child and Adolescent Psychiatry 40, 685–95.

Reiss S. & Szyszko J. (1983) Diagnostic overshadowingand professional experience with mentally retardedpersons. American Journal of Mental Deficiency 87, 396–402.

Rose E., Bramham J., Young S., Paliokostas E. & XenitidisK. (2009) Neuropsychological characteristics of adultswith comorbid ADHD and borderline/mild intellectualdisability. Research in Developments Disabilities 30, 496–502.

Sevin J. A., Bowers-Stephens C. & Crafton C. G. (2003)Psychiatric disorders in adolescents with developmental




disabilities: longitudinal data on diagnostic disagreementin 150 clients. Child Psychiatry and Human Development34, 147–63.

Simonoff E., Pickles A., Wood N., Gringras P. & Chad-wick O. (2007) ADHD symptoms in children with mildintellectual disability. Journal of the American Academy ofChild and Adolescent Psychiatry 46, 591–600.

Suhr J., Zimak E., Buelow M. & Fox L. (2009) Self-reported childhood attention-deficit/hyperactivity disor-der symptoms are not specific to the disorder.Comprehensive Psychiatry 50, 269–75.

Tonge B. & Einfeld S. (2000) The trajectory of psychiatricdisorders in young people with intellectual disabilities.Australian and New Zealand Journal of Psychiatry 34,80–4.

Toone B. (2004) Attention deficit hyperactivity disorder inadulthood. Journal of Neurology, Neurosurgery, and Psy-chiatry 75, 523–5.

Wechsler D. (1997) Wechsler Adult Intelligence Scale (WAIS-III). Pearson Education Ltd, Oxford.

Wechsler D. (1999) Wechsler Abbreviated Scale of Intelligence(WASI). Pearson Education Ltd, Oxford.

Zwi M. & York A. (2004) Attention-deficit hyperactivitydisorder in adults: validity unknown. Advances in Psychi-atric Treatment 10, 248–59.

Accepted 24 February 2010


