A clinical study of attention-deficit/hyperactivity disorder in preschool children—prevalence and differential diagnoses

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Brain & Development xxx (2013) xxx–xxx

Original article

A clinical study of attention-deficit/hyperactivity disorderin preschool children—prevalence and differential diagnoses

Kenji Nomura a,⇑, Kaori Okada a, Yoriko Noujima b, Satomi Kojima b, Yuko Mori a,Misuzu Amano a, Masayoshi Ogura c, Chie Hatagaki d, Yuki Shibata a, Rie Fukumoto a

a Center for Developmental Clinical Psychology and Psychiatry, Nagoya University, Nagoya, Japanb Kanie Health Center, Aichi, Japan

c Graduate School of Education, Naruto University of Education, Naruto, Japand Faculty of Humanities and Social Sciences, Shizuoka University, Shizuoka, Japan

Received 7 May 2013; received in revised form 12 November 2013; accepted 14 November 2013

Abstract

Objective: We aimed to examine (1) the prevalence and characteristics of ADHD in preschool children, and (2) differentialdiagnoses among children who display symptoms of inattention and hyperactivity–impulsivity in early childhood. Methods: Theparticipants were children living in Kanie-cho, in Japan’s Aichi Prefecture, who underwent their age 5 exams at the municipal healthcenter between April 2009 and March 2011. We first extracted children who were observed to be inattentive or hyperactive–impulsive during their age 5 exams and considered as possibly having ADHD. We conducted follow-ups with these children usingpost-examination consultations, visits to preschools, and group rehabilitation. The results of the age 5 exams were combined withbehavior observations and interview content obtained during subsequent follow-ups. A child psychiatrist and several clinical psy-chologists discussed these cases and made a diagnosis in accordance with the DSM-IV-TR. Results: 91 (15.6%) of the 583 childrenselected were considered as possibly having ADHD; we were able to conduct follow-ups with 83 of the 91 children. Follow-up resultsshowed that 34 children (5.8% of all participants) remained eligible for a diagnosis of ADHD. Diagnoses for the remaining childrenincluded: pervasive developmental disorders (six children, or 6.6% of suspected ADHD children), intellectual comprehension prob-lems (four children, or 4.4%), anxiety disorders (seven children, or 7.7%), problems related to abuse or neglect (four children, or4.4%), a suspended diagnosis for one child (1.1%), and unclear diagnoses for 29 children (31.9%). Conclusions: ADHD tendenciesin preschool children vary with changing situations and development, and the present study provides prevalence estimates thatshould prove useful in establishing a diagnostic baseline.� 2013 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.

Keywords: Attention-deficit/hyperactivity disorder (ADHD); Preschool children; Prevalence; Differential diagnoses

1. Introduction

Attention-deficit/hyperactivity disorder (ADHD) ischiefly characterized by attention deficits, hyperactivity,

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http://dx.doi.org/10.1016/j.braindev.2013.11.004

⇑ Corresponding author. Address: Center for DevelopmentalClinical Psychology and Psychiatry, Nagoya University, Furo-cho,Chikusa-ku, Nagoya City, Aichi 464-8601, Japan. Tel.: +81 52 7892611; fax: +81 52 747 6522.

E-mail address: [email protected] (K. Nomura).

Please cite this article in press as: Nomura K et al. A clinical study of attenand differential diagnoses. Brain Dev (2013), http://dx.doi.org/10.1016/j.b

and impulsivity. The condition causes behavior prob-lems and difficulties in relationships, and may lead topoor adaptation to group activities [1]. Moreover, dueto impulsivity and underdeveloped behavior control,ADHD complicates child-rearing; this results in highlevels of stress for guardians, and may significantly raisethe risk of maltreatment [2,3]. After entering elementaryschool, maladaptation is marked by difficulty in sittingstill, learning difficulties, and problems with group activ-ities; this is when those around the child begin to notice

logy. Published by Elsevier B.V. All rights reserved.

tion-deficit/hyperactivity disorder in preschool children—prevalenceraindev.2013.11.004


mailto:[email protected]



2 K. Nomura et al. / Brain & Development xxx (2013) xxx–xxx

problems. Continued maladaptation results in psycho-logical issues, which may make adaptation more difficultstill. Therefore, in addition to early detection, youngchildren with ADHD require understanding and sup-port from those around them.

In Japan, municipalities conduct health examinationsfor young children in order to detect developmental dis-orders at an early stage. These examinations, conductedat health centers all across Japan, are generally con-ducted at four months, 18 months, and three years.The objectives of these examinations are the detectionof, and support for, child developmental problems, aswell as child-rearing support for guardians of childrenwith such problems. More than 90% of children inJapan undergo these assessments, which play a largerole in the early detection of developmental disorders.In order to screen for developmental disorders, hyperac-tivity figures as a test item; however, hyperactivity–impulsivity and attention/concentration difficulties arenonspecific symptoms in developing preschool children.Therefore, in order to determine which children trulyrequire support, and to provide it in the appropriateway, we must elucidate the actual presentation ofADHD in preschool children.

Studies in other countries have estimated the preva-lence of ADHD in preschool children to be 1.9–5.7%,with no major difference in prevalence during elemen-tary school [4–9]; research also suggests that early child-hood symptoms remain after entering elementary school[10–12]. On the other hand, early childhood cases maypossess distinctive characteristics. For example, thereare several predominantly hyperactive–impulsive typecases, while there are few predominantly inattentive typecases [9]. However, there is a dearth of Japanese studieson early childhood ADHD; this is troublesome, becauseADHD prevalence may be affected by culture, resultingin differences among countries and regions [9,13,14].We, therefore, believe that understanding the currentstatus of ADHD in Japan is crucial.

Thus, using follow-ups from age 5 municipal healthexaminations, we examined (1) the prevalence and char-acteristics of ADHD in preschool children, as well as (2)differential diagnoses among children who display symp-toms of inattention and hyperactivity–impulsivity inearly childhood.

2. Participants and methods

2.1. Participants

Participants were children living in Kanie-cho, Japan’Aichi Prefecture, who had turned 5 years old and under-went their age 5 exams at the municipal health centerbetween April 2009 and March 2011. When notices weremailed regarding these exams, parents also received theenclosed written explanation of the study. This explana-


tion requested consent to use the results of the exam, aswell as those of the follow-up, for our research. All chil-dren for whom consent was obtained were used as sub-jects. This study was conducted with the approval of theNagoya University School of Medicine InstitutionalReview Board (consent #624).

2.2. Methods

First, we extracted children whom we observed to beinattentive or hyperactive–impulsive during their age 5exams, suggesting the possibility of ADHD. We thenconducted follow-ups with these children using post-examination consultations, visits to kindergartens andnursery schools (hereafter collectively referred to as“preschools”), and group rehabilitation sessions.

2.2.1. Assessments of age 5 exams

In order to find out the possibility of ADHD in theage 5 exams, the assessment was carried out with the fol-lowing information:

(a) The child’s guardian answered behavior-relatedquestions in an interview sheet (e.g., “The childis: restless, able to wait for a turn, able to acttogether when going outside or shopping, able tomove to next activity soon even when playtimeor television is interrupted,” etc.).

(b) The kindergarten teacher answered behavior-related questions in an interview sheet (e.g., “Thechild is able to listen while sitting down on a chair,able to concentrate and engage on a problem, ableto move to the next activity smoothly even whenplaying,” etc.).

(c) A physician or psychologist carried out behaviorobservations during a group activity that we setup for approximately 30 min (observation points:whether the child was able to hold his/her atten-tion, fell for stimuli, was able to listen while sitting,understood activity rules, etc.).

(d) A public health nurse interviewed the child’sguardian.

(e) Individually conducted developmental tests (testitems consisted of numerical concepts, understand-ing words and expressions, and drawing figures).

(f) Individually conducted motor examinations. (Theexamination evaluated upper and lower limbmotor functions; the items required children toboth stand and jump on one leg, and tap theirfingers.)

(g) A physician or psychologist carried out behaviorobservations during the developmental and motorexaminations (observation points: whether thechild was able to perform the task while stayingcalm, able to obey instruction, or able to keephis/her attention).



K. Nomura et al. / Brain & Development xxx (2013) xxx–xxx 3

Based on the above information, a child psychiatristconducted an examination of the child while the guard-ian was present; this examination was the final assess-ment of the age 5 exam. Guardians of children whomwe suspected of having ADHD received an explanationof the condition, as well as a recommendation for a fol-low-up.

This follow-up was conducted in the form of a post-examination consultation or a preschool visit. Duringthe follow-up, participation during group rehabilitationfor upper-year preschool children (5–6 years old) wasrecommended when necessary.

2.2.2. Follow-ups

2.2.2.1. Post-examination consultations. We conducteddevelopmental consultations at health centers approxi-mately once or twice per month. Following an interviewconducted by a public health nurse, a child psychiatristor clinical psychologist conducted a second interview.During these consultations, the child was also present.The child was interviewed, and his or her behaviorwas observed during free play. Records of the child’sinterview and behavioral observation were combinedwith the record of the guardian’s interview to assessthe child’s symptoms and developmental characteristics.This assessment was then used to provide advice andinstruction to the guardian.

2.2.2.2. Preschool visits. Between May and July, we vis-ited upper-year classes at all 10 Kanie-cho preschools.During these visits, a child psychiatrist, a clinical psy-chologist, and a public health nurse observed target chil-dren, and conducted oral interviews with their teachers.Target children were children whose guardians providedconsent for these visits during the age 5 exams. Weasked each child’s teacher to complete a form prior tothe visit that dealt with the child’s family, daily activi-ties, motor skills (gross motor skills and fine motorskills), language skills (comprehension and expression),relationships with others (teachers and children), playactivities, and problem behaviors. On the day of thevisit, our staff observed the child for 1–2 h in the morn-ing and assessed his/her adaptation to group activities.In the afternoon, we examined the target child’s casewith his/her teacher and relevant faculty members.During the case examination, we listened to the child’steacher’s assessment regarding the child’s behavior,activity status, and developmental characteristics, andprovided advice and instruction to the teacher.

2.2.2.3. Group rehabilitation. This refers to group reha-bilitation for upper-year preschool children. We con-ducted two courses of rehabilitation (May–August andSeptember–December), and held individual interviewswith guardians before and after the course. Each reha-


bilitation session lasted roughly one hour. These ses-sions consisted of social skills training for children,and group counseling for guardians. Our research groupwas in charge of rehabilitation, behavior observationduring rehabilitation, group counseling with guardians,and individual interviews with guardians.

2.2.3. Assessment of target children

We combined the results of the age 5 exam anddetails of the children’s psychiatric evaluations withthe behavior observations and interview contentobtained during subsequent follow-ups (post-examina-tion consultations, preschool visits, and group rehabili-tation). Using this information, an experienced childpsychiatrist and several clinical psychologists discussedcases and made a diagnosis based on the Diagnosticand Statistical Manual of Mental Disorders Fourth Edi-tion Text Revision (DSM-IV-TR) [1].

3. Results

In Kanie-cho, 585 5-year-olds received the examina-tion during this study period (visiting rate: 87.2%). Weobtained informed consent from 583 children (300 boys,283 girls), among whom we suspected 91 (15.6%) of hav-ing ADHD (hereafter referred to as ADHD suspectedchildren; 81 boys, 10 girls) based on our examination.

We conducted follow-ups with 83 of these 91 chil-dren. Follow-ups consisted of a post-examinationconsultation for one child, a preschool visit for 43 chil-dren, and both a post-examination consultation andeither a preschool visit or group rehabilitation for 39children. Of the eight children with whom we couldnot conduct follow-ups, four did not take part due toguardian reluctance, and four moved away.

Thirty-four children (5.8% of all subjects) were con-sidered to have ADHD (see Table 1). All 34 childrenwere male. According to the ADHD subtypes withinthe DSM-IV-TR, 11 children (1.9%) were predomi-nantly hyperactive–impulsive type, 19 (3.3%) were ofthe combined type, and four (0.7%) were classified aspredominantly inattentive type. We observed the follow-ing comorbidities: oppositional defiant disorder (ODD)among five children (14.7% of ADHD children), mentalretardation (MR) in one child (2.9%), dysarthria amongtwo children (5.9%), and separation anxiety disorder inone child (2.9%). Conduct disorder (CD) was notobserved.

Of the 91 suspected ADHD children, 34 (37.4% ofsuspected ADHD children) were ultimately received adiagnosis of ADHD. Diagnoses among other childrenincluded pervasive developmental disorders (PDD)among six children (6.6%), intellectual/comprehensionproblems (suspicion of MR or borderline impaired intel-ligence) among four children (4.4%), anxiety disordersamong seven children (7.7%; this includes one child



Table 2Cases that did not present with a clear diagnosis.

Totals Boys Girls

Mild ADHD tendencies not meet the criteria 11 9 2ADHD tendencies improved 3 3 0Severe anxiety or tension 4 3 1Restless with their families 3 3 0No problems 8 8 0Totals 29 26 3

Table 1The result of follow-ups with suspected ADHD children.

Totals Boys Girls

Maindiagnosis (%)

Comorbidity

ADHD 34 (37.4) 34 0PDD 6 (6.6) 5 1Intellectual/comprehensionproblems

4 (4.4) 1 2 2

Anxiety disorders 5 (5.5) 2 4 0Abuse or neglect 4 (4.4) 3 1Suspended diagnosis 1 (1.1) 0 1No clear diagnosis 29 (31.9) 27 3Could not conductfollow-ups

8 (8.8) 6 2

Totals 91 (100.0) 3 81 10

ADHD, attention-deficit/hyperactivity disorder; PDD, pervasivedevelopmental disorders.


who also had ADHD or PDD; generalized anxiety dis-order among four children, separation anxiety disorderin one child, and anxiety disorder not otherwise specifiedamong two children), problems related to abuse orneglect among four children (4.4%; psychological abuseamong three children, two of whom also displayed phys-ical abuse; neglect was observed in one child), a sus-pended diagnosis for one child (1.1%), and uncleardiagnoses for 29 children (31.9%).

Of the 29 children who did not present with a cleardiagnosis is as follows, eleven presented with mildhyperactivity or attention problems, which did not meetthe criteria for a diagnosis of a developmental disorder.Three children were observed to have ADHD tendenciesduring their age 5 exams, but these tendencies subse-quently improved. Four children presented with severeanxiety or tension. Three children were restless withtheir families, but showed no problems during normalschool activities. No problems were observed amongeight children (see Table 2).

4. Discussion

4.1. Prevalence of ADHD in preschool children

Japan has produced scant research on the prevalenceof ADHD in preschool children. Following up with 978


children after undergoing an 18-month health examina-tion, Yoshikawa [15] diagnosed 28 children of the sam-ple (2.9%) with ADHD from behavioral observationsconducted during the upper year of preschool. Soma[16] created a questionnaire based on the Diagnosticand Statistical Manual of Mental Disorders, Third Edi-tion, Revised (DSM-III-R) to survey 7566 guardians ofchildren aged 3–5 and 9956 preschool teachers; 31.1% ofguardians’ responses and 4.3% of teachers’ responsesmet criteria for ADHD. Finally, Koeda [17] found that60 of 1359 children (4.7%) were suspected to haveADHD based on age 5 exams, and Shimoizumi [18]found that 8 of 736 children (1.1%) were suspected tohave ADHD (also based on age 5 exams).

Reports outside of Japan have estimated the preva-lence of ADHD in preschool children to be 1.9–12.8%[4–9]. Using health examinations designed for 4-year-old children living in Trondheim, Norway, Wichstromand colleagues [9] administered a questionnaire measur-ing overall adaptation (Strengths and Difficulties Ques-tionnaire; SDQ) as well as a standardized structuredinterview (Preschool Age Psychiatric Assessment;PAPA) to 995 guardians of preschool children. Theprevalence of ADHD with maladaptation was 1.9%(hyperactive–impulsive type predominated with 1.6%,with combined type being 0.3%, and predominantlyinattentive type being 0.2%), while the prevalence ofADHD—regardless of adaptation—was 2.2%. ADHDwas present in 2.4% of boys and 1.5% of girls; thus,ADHD was 1.7 times more prevalent among boys.ODD was also present in 20.8% of the ADHD cases,while 14.4% of the ADHD cases also presented withCD. Lavigne and colleagues [8] administered a stan-dardized, structured interview (Diagnostic InterviewSchedule for Children-Parent Scale – Young Child Ver-sion; DISC-YC) to guardians of 796 4-year-old childrenrecruited individually at preschools and pediatric clinics.12.8% of children received a diagnosis of ADHD (6.9%hyperactive–impulsive type; 4.2% combined type; 1.8%inattentive type). The ratio of boys to girls with ADHDwas 1.6:1. Egger and colleagues [5] also conducted stan-dardized structured interviews (PAPA) with the guard-ians of 307 children aged 2–5 who attended a pediatricclinic; they reported an ADHD prevalence of 3.3%. Lav-igne and colleagues [7] conducted a study with 510 chil-dren aged 2–5 attending a clinic; the study employedoral surveys with standardized items, questionnaires,and analysis of videos wherein children played with theirparents. Two psychologists, who then made diagnoses,assessed these measures independently. The psycholo-gists determined ADHD in 2% of the children, with a1.9:1 ratio of boys to girls. Keenan and colleagues [6]conducted non-standardized structured interviews (K-SADS) with the guardians of 104 4-year-old children liv-ing in poverty; they reported that ADHD manifested in5.7% of the children. However, due to a social class bias




in the target group, whether or not these results apply totypical preschool children is uncertain [9]. Finally, Earlsand colleagues [4] conducted interviews with parents of100 3-year-old children living on an island and observedthe children at play for one hour; they reported ADHDin 2% of the sample.

The prevalence of ADHD in the present study was5.8%, which is not very different from previous studies.When classified into subtypes, the prevalence of thehyperactive–impulsive type was 1.9%, with combinedtype and inattentive types at 3.3% and 0.7%, respectively.Although there was a higher percentage of combinedtype cases than in previous studies, predominantlyinattentive type cases tended to be infrequentlyobserved—a common finding in previous studies.Regarding comorbid disorders, ODD was observed in14.7% of the ADHD cases, while CD was not observed.

The ratio of boys to girls with ADHD in previousstudies was 1.6–1.9:1—not markedly different from theratio among school-age children. However, while therewere 34 boys (11.3%) in the present study who were con-sidered to have ADHD, no girls received this diagnosis;it is unclear which particular factors are responsible forthis finding. We should note that the present studyplaced greater focus on group activities in preschoolthan previous research; therefore—because maladapta-tion to group activities and difficulties in relationshipsdo not manifest as clearly, or become as problematic,in girls as in boys—the girls’ symptoms may not havebeen evident. Although 10 girls were considered to haveADHD tendencies during their age 5 exams, two ofthem were considered to present with mild ADHDsymptoms that did not warrant an official ADHD diag-nosis. During group activities, mild symptoms are easierto see in boys than in girls; therefore, girls’ symptomsmay not have reached the diagnostic threshold. In thefuture, it may therefore be necessary to increase thenumber of children and conduct reexamination payingparticular attention to such diagnostic subtleties.

4.2. Differential diagnoses of ADHD in preschool children

4.2.1. PDD diagnosis

Of the 91 children whom we observed to exhibitADHD tendencies during their age 5 exams, we foundsix children (6.6%) to have PDD during follow-ups.

Differential diagnosis between ADHD and PDD isoften difficult. Various reports have stated that 38–68% of school-age high-functioning PDD patients fulfillthe DSM-IV-TR diagnostic criteria for ADHD [19–21].In order to differentiate between the two, it is necessaryto examine whether PDD symptoms are present. How-ever, in an examination of five cases whose diagnoseschanged from ADHD to PDD, Kinouchi [22] stated thatdifficulties in interpersonal relationships are morenoticeable through late school age; during this period,


hyperactivity is prominent and easily noticed, increasingthe probability of an ADHD diagnosis. Kawatani [23]compared 66 cases whose diagnoses were changed fromADHD to PDD, to 135 cases whose diagnoses were notchanged. The results indicated that PDD characteristicsbecame apparent as individuals aged; in some cases,however, researchers judged the children to have comor-bid PDD.

In the present study, some suspected ADHD caseswere diagnosed as PDD during follow-ups. In thesecases, easily noticed symptoms—such as hyperactivityand inattentiveness—were prominent during shorthealth examinations; impairments and particularities insocial relationships characteristic to PDD, meanwhile,were difficult to assess in a short period. Through fol-low-ups, children’s group activities and relationshipswere observed at preschool, and details regardingbehavior at preschool and at home were obtained.Doing so helped clarify PDD characteristics that chil-dren had previously possessed. It may also be possiblethat, as time progresses, PDD characteristics willbecome evident with successive follow-ups.

4.2.2. Intellectual/comprehension problems

We found intellectual/comprehension problemsamong four children (4.4%; one of whom also hadADHD) in the present study. Individual developmentaltests could not be conducted in some cases; in others, theprecise degree of intellectual impairment was difficult toascertain. However, diagnoses were made based on theresults of developmental tests during health examina-tions, as well as achievement level on tasks and compre-hension of directions in preschool.

Intellectual/comprehension problems are difficult todifferentiate from attention deficit in certain cases. Inthe ADHD entry from the DSM-IV-TR, mental retar-dation is given as a differential diagnosis: “In childrenwith mental retardation, an additional diagnosis ofADHD should be made only if the symptoms of inatten-tion or hyperactivity are excessive for the child’s mentalage,” and, “Symptoms of inattention are commonamong children with low IQ who are placed in academicsettings that are inappropriate to their intellectual abil-ity.” [1] In other words, it is necessary to consider bothof the following possibilities: underdeveloped behaviorcontrol due to mental retardation, itself presents withsymptoms of inattentiveness and hyperactivity. Addi-tionally, children with mental retardation present withsymptoms of inattentiveness as a manifestation of themaladaptation they experience due to their poorcomprehension.

In the present study, symptoms of inattentiveness andhyperactivity within group settings were evident duringhealth examinations; therefore, the possibility of ADHDwas considered. By assessing levels of achievement andobserving daily life tasks during subsequent follow-




ups, we were able to differentiate between ADHD andmental retardation.

4.2.3. Anxiety disorders

Anxiety disorders were observed among seven chil-dren (7.7%). Four children had generalized anxiety dis-order, one child had separation anxiety disorder, andtwo children had anxiety disorder not otherwisespecified.

In the diagnostic criteria for generalized anxiety dis-order, the DSM-IV-TR lists restlessness, difficulty con-centrating, and irritability as symptoms of anxiety andworry. These indications resemble inattentiveness andhyperactivity–impulsivity, which are the core symptomsof ADHD. The diagnostic criteria for ADHD in theDSM-IV-TR exclude anxiety disorders, which are alsoconsidered to be important as differential diagnoses inpreschool children.

4.2.4. Problems related to abuse and neglect

Problems related to abuse were observed among threechildren, while problems related to neglect wereobserved in one child. Mothers psychologically abusedall three children who presented with problems relatedto abuse; mothers, or a male living with them, physicallyabused two of these children. High degrees of impulsiv-ity were observed among all three children. In responseto trivial matters, all three children were observed to losetheir tempers, use abusive language, and act outviolently.

Several previous reports have stated that abused chil-dren often present with ADHD symptoms [24–27]. Thepossible causes are posttraumatic stress disorder (hereaf-ter referred to as “PTSD”) accompanied by increasedarousal and dissociation accompanied by altered con-sciousness. PTSD is frequently observed among abusedchildren; the DSM-IV-TR lists irritability, outbursts ofanger, and difficulty concentrating as increased arousalsymptoms. In an examination of abused children whounderwent treatment at a children’s hospital, Endoand colleagues [28] found that 67% of children fulfilledthe diagnostic criteria for ADHD; only 27% displayedADHD symptoms before abuse, while the remaining40% displayed symptoms after it. Moreover, the 40%of children with newly presented ADHD symptoms ful-filled the diagnostic criteria for dissociative disorder.These symptoms are frequently considered to resemblethe attention deficit and hyperactivity–impulsivityaspects of ADHD.

The mother of the neglected child was limited in hercapacity as a caretaker and was almost never urged tocare for her child. At preschool, the child was often ina daze and exhibited little reaction when called on byteachers or friends; these characteristics resemble thoseof attention deficit.


4.2.5. Cases that did not display clear diagnoses

In total, we found indications that 29 children(31.9%) may be eligible for an ADHD diagnosis andwere followed up, but ultimately did not display a clearpsychiatric diagnosis.

An examination of case details shows that, while weinitially observed ADHD symptoms in nearly half ofthese cases (14 children), these symptoms were mild ordid not fulfill diagnostic criteria. Among preschool chil-dren, mild difficulties with attentiveness and hyperactiv-ity–impulsivity are frequently observed in healthychildren as well, and are therefore nonspecific symp-toms. In fact, the DSM-IV-TR notes, “it is difficult toestablish this diagnosis in children younger than age 4or 5 years, because their characteristic behavior is muchmore variable than that of older children and mayinclude features that are similar to symptoms ofADHD” and, “Because many overactive toddlers willnot go onto develop ADHD, special attention shouldbe paid to differentiating normal overactivity from thehyperactivity characteristic of ADHD before makingthis diagnosis in early years.” [1]. Yoshikawa [15] statesthat children who were hyperactive at the outset of earlychildhood separated in early childhood’s latter half intotwo groups: the hyperactivity of children in the firstgroup improved; that of children in the second groupdid not, and they developed ADHD. Follow-up obser-vation was necessary for these children. In the presentstudy, some children who presented with ADHD symp-toms during the age 5 exams showed improvement inADHD symptoms at the time of follow-up, and we wereable to discern between these groups. Moreover, byassessing the severity of ADHD symptoms, we were ableto differentiate ADHD children from those whose symp-toms did not qualify as ADHD.

There were also some children who, although display-ing favorable adaptation in daily activities during fol-low-ups, displayed severe anxiety or tension, orbecame restless in front of their families; it is likely thatthese characteristics affected the children’s states on theday of the initial exam. Differentiation became possibleby conducting a second assessment at a different timeand place, and by obtaining information from an adultwho was familiar with the child in daily life.

4.2.6. Study issues and limitationsThe present study examined the prevalence and differ-

ential diagnoses of ADHD in preschool children by con-ducting follow-up examinations with 583 children whounderwent age 5 exams. There is a dearth of epidemio-logical studies concerned with early childhood ADHDin Japan. Moreover, research conducted in other coun-tries shows that there are few studies using communitysamples. The present study is, therefore, a useful addi-tion to the early childhood ADHD literature.




The largest limitation of the present study is thatdiagnostic interviews were not conducted with everychild’s guardians. However, during the age 5 exams,we directly observed all children during group activitiesand while performing individual tasks (developmentaland motor tests). We also obtained detailed informationthrough public health nurses’ oral interviews withguardians. Child psychiatrists then used this informa-tion to conduct interviews. In addition, in almost allcases, we conducted follow-ups that consisted of behav-ior observation within a preschool or group rehabilita-tion context, as well as detailed oral interviews withpreschool teachers.

The diagnostic criteria for ADHD in the DSM-IV-TRare as follows: (A) inattention or hyperactivity–impulsiv-ity persisting for at least six months; (B) symptoms werepresent before age 7 years; (C) the disorder is present intwo or more settings; (D) there are clear evidence ofclinically significant impairment; (E) there are no othermental disorders or mental illnesses responsible forADHD symptoms [1].

In previous studies, diagnostic assessments tended torely on one point in time or one scenario. Moreover,while some studies obtained written information fromteachers, interviews for obtaining detailed informationfor making a diagnosis were conducted solely withguardians. Therefore, the DSM-IV-TR diagnosticcriteria (A) and (C) were, often, technically unfulfilled.Furthermore, some research did not assess clinical disor-ders; these studies failed to meet diagnostic criterion(D).

With the exception of one child who, following a clin-ical interview, was cleared of mental problems, all casesin the present study underwent assessment at a mini-mum of two locations and points in time: during themunicipal age 5 exam (middle year of preschool; age4–5) and at the preschool follow-up (upper year of pre-school; age 5–6). Thus, the present study confirmed thecriteria: inattentiveness or hyperactivity–impulsivitycontinued for six months for (A); symptoms were pres-ent before age 7 for (B); and the disorder was presentin two or more situations for (C). Moreover, (D) and(E) were fulfilled by assessments performed duringdetailed oral interviews at the age 5 exams and duringfollow-ups.

Compared to previous research, the present studywas limited because structured interviews were not cen-tral to diagnosis. Despite the limitations, the relativestrengths—a detailed examination at the first screening(age 5 exam), and the assessment of children at twopoints in time, as well as two different contexts—lenda notable degree of legitimacy to our findings.

Another limitation of the present research was thatfollow-ups were limited to the period preceding elemen-tary school. ADHD tendencies in preschool childreneasily vary with changing situations and development,


complicating diagnosis. Moreover, maladaptation inADHD becomes prominent after entering elementaryschool. In particular, symptoms of inattention are scar-cely noticeable in preschool children but become prob-lematic during elementary school. Some reports haveshown that ADHD diagnoses made in preschool chil-dren subsequently stabilize. However, for the presentstudy, we would like to perform further follow-ups inthe future to clarify whether ADHD diagnoses havestabilized.

Future studies should examine details, such ascomorbid disorders, ADHD subtypes, gender ratios,and differential diagnoses, with a larger sample sizeand several follow-ups spread across time. Additionalresearch should also include structured interviews,which will be conducted with every child’s guardian.

Acknowledgments

The present study was conducted as a part of theTherapeutic Educational Support Project for Develop-mental Disorders, funded by a special education re-search grant from the Ministry of Education, Culture,Sports, Science and Technology.

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Documents

A clinical study of attention-deficit/hyperactivity disorder in preschool children—prevalence and differential diagnoses