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Aims: To clarify differences in objective activity levels between children with attention-deficit/hyperactivity disorder (ADHD) and those with pervasive developmental disorders (PDD) and hyperactivity.
Method: Eighteen boys with combined type ADHD, 10 boys with PDD with hyperactivity, and 18 control boys wore actigraphs for 1 week while attending elementary school. In addition to the average activity level, the standard deviation in the activity levels were compared for two continuous situations: (i) in-seat classes, in which the participants were expected to sit in their own seats and learn quietly; and (ii) free recess periods following the in-seat classes.
Results: All the groups were affected by the situational shift, the average activity level of each the groups was higher and the standard deviation was smaller than those during the in-seat classes. The boys with ADHD exhibited a still smaller standard deviation than the controls and the boys with PDD and hyperactivity during the free recess period; no difference between the controls and the boys with PDD was seen. The boys with PDD exhibited a significantly lower average activity level than the other groups. No differences among the groups in the average activity levels and standard deviation were seen during the in-seat classes.
Conclusions: The observed objective activity levels in each group reflect the degree to which the boys are able to tolerate changes in situations. Objective measurement of activity levels may be useful to differentiate hyperactivity in children with ADHD from that in children without ADHD.
ATTENTION-DEFICIT/HYPERACTIVITY DISORDER (ADHD) is characterized by developmentally inappropriate symptoms of inattention and/or hyperactivity/impulsivity.1 It is one of the most common childhood-onset psychiatric disorders, affecting 3–7% of children. The DSM-IV indicates that the symptoms of ADHD are affected by several situational factors, such as time of day, fatigue, repetition of instructions, supervision, and others.1,2
Previous studies have reported that the objective activity levels of children with ADHD were also affected by situational factors. An actigraph, which reflects changes in the frequency of body movements, is an acceleration-sensitive device with a solid-state memory system that records the number of movements performed by a child per unit of time. During structured situations such as reading and math classes, laboratory-based attention tasks, and structured afternoon sessions, children with ADHD were more active than children without ADHD.3–8 No differences in the groups were seen, however, during less structured situations. The differences in the objective activity levels between children with ADHD and without ADHD might be identified when several situational factors overlapped.8
Although the DSM-IV criteria for ADHD exclude comorbid diagnosis of pervasive developmental disorders (PDD), some clinicians have found that children with PDD often present with interfering hyperactivity, distractibility, and impulsiveness, and note that a comorbid diagnosis of ADHD in children with PDD is the implementation of effective treatment.9–12 Methylphenidate, however, is often efficacious in treating hyperactivity associated with PDD, but the magnitude of response is less than that seen in typically developing children with ADHD.13 PDD comprise a group of neuropsychiatric disorders characterized by specific delays and deviances in social, communicative, and cognitive development, with onset typically in the first years of life. Generally, children with PDD often have difficulty tolerating change and variations in their daily situations, and this characteristic is different from the situational variability in the symptoms of ADHD. It remains controversial whether hyperactivity in children with PDD arises from comorbid ADHD or is an intrinsic symptom of PDD.
Few studies, if any, have examined differences in objective activity levels between children with ADHD and those with PDD and hyperactivity and/or impulsiveness. The present study investigated differences in objective activity levels between boys with ADHD and boys with PDD and hyperactivity. In addition to calculating the average activity levels as a quantitative measure of movement, we calculated the standard deviation as a measure of the temporal variability in the activity level: in other words, the standard deviation represents a measure of the spread of the objective activity levels. We examined the following two continuous settings to clarify the differences in the activity levels between the groups: (i) in-seat classes, in which the participants were expected to sit in their own seats and learn quietly; and (ii) free recess periods following the in-seat classes.
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We recruited 18 boys (age range, 7–11 years) who met the DSM-IV criteria for ADHD combined type and who were being treated at Kinki University Hospital and Kakunishikawa Clinic. Ten other boys (range, 7–12 years) who met the DSM-IV criteria for Asperger disorder (n = 3) or unspecified PDD (n = 7) were also recruited. All the boys with PDD had interfering symptoms of hyperactivity and/or impulsiveness that had been present for at least 6 months that had begun prior to the age of 7 years. The severity of hyperactivity and/or impulsiveness was confirmed by a parent interview and on the Child Behavior Check List (CBCL) and the Teacher Report Form for the CBCL (TRF).14,15 The diagnoses were based on psychiatric interviews conducted by trained clinicians and were confirmed using a semi-structured parent interview form.16 The exclusion criteria were (i) full-scale IQ < 70, as assessed using the Wechsler Intelligence Scale for Children, third edition (WISC-III);17 (ii) serious medical condition or neurological illness; (iii) history of psychosis or bipolar disorder; and (iv) history of abuse.
Eighteen control boys (range, 7–12 years) were recruited from local elementary schools; none of the control subjects had ADHD, as determined by the responses obtained during a parent interview regarding the ADHD symptoms listed in the DSM-IV criteria. The exclusion criteria were (i) IQ < 85, as assessed using the Kohs Block Design Test;18 (ii) any psychiatric or neurological disorder; (iii) history of psychosis or bipolar disorder; and (iv) history of abuse.
Written informed consent was obtained from all the participants and their parents after the procedure had been explained to them in detail. Three boys with ADHD met the criteria for oppositional defiant disorder. Four boys with ADHD were receiving methylphenidate medication and were required to discontinue this treatment for at least 48 h before the start of actigraphic monitoring to ensure a complete washout of this agent.
No significant difference in age was observed among the three groups. No significant difference in full-scale IQ was observed between the boys with ADHD and the boys with PDD (Table 1), although no reference was available for the correlation between the WISC-III and the Kohs Block Design Test. The CBCL and the TRF T scores (total, externalizing problems, attention problems, delinquent problem, and aggressive problem) were similarly high for the ADHD and PDD groups. The CBCL attention problems scale have the highest discriminating power for ADHD.19 Further, the CBCL externalizing, delinquent, and aggressive problems scales and the TRF delinquent problem scale discriminate ADHD combined type and PDD with hyperactivity from PDD without hyperactivity; no significant differences between ADHD and PDD with hyperactivity were seen.20 In the present study the boys with PDD had clinical hyperactivity and/or impulsiveness similar to the boys with ADHD.
Table 1. Subject characteristics
| ||Boys with ADHD (n = 18)||Boys with PDD and hyperactivity (n = 10)||Control boys (n = 18)||Statistics|| P |
|Age (years)|| ||9.33 ± 1.41||9.2 ± 1.75||9.17 ± 1.2||H = 0.25||0.88|
|IQ|| ||93 ± 10.61†||99.4 ± 16.95†||>85‡|| t (d.f. = 26) = 1.23||0.23|
|CBCL||Total§||65.78 ± 6.81||69.4 ± 8.58||–|| t (d.f. = 26) = 1.32||0.2|
|Externalizing problem§||68.2 ± 10.5||68.1 ± 11.1|| || t (d.f. = 26) = 0.02||0.99|
|Attention problem§||67.39 ± 9.55||72.2 ± 8.6||–|| t (d.f. = 26) = 1.23||0.22|
|Delinquent problem§||62.8 ± 8.2||64.0 ± 7.6|| ||Z = –0.36||0.7|
|Aggressive problem§||68 ± 9.8||70.4 ± 12.6|| || t (d.f. = 26) = 0.46||0.65|
|TRF||Total§||68.17 ± 7.72||66.6 ± 5.93||–|| t (d.f. = 26) = 0.56||0.56|
|Externalizing problem§||70.0 ± 8.8||66.2 ± 9.3|| || t (d.f. = 26) = 1.07||0.29|
|Attention problem§||66.0 ± 8.1||66.6 ± 7.46||–|| t (d.f. = 26) = 0.19||0.85|
|Delinquent problem§||63.4 ± 7.5||64.2 ± 6.6|| || t (d.f. = 26) = 0.29||0.78|
|Aggressive problem§||69.9 ± 12.1||66.6 ± 10.8|| ||Z = 0.41||0.68|
The diagnoses of ADHD combined type and PDD were confirmed using a semi-structured parent interview form.16 This form was modified from a clinical interview form for parents that was initially developed by Barkley and Murphy;21 the modified form included some additional items. The parent interview form covered the child's developmental history and all the symptoms of ADHD, oppositional defiant disorder, conduct disorder, other axis I psychiatric disorders, and PDD, as outlined by the DSM-IV criteria. This parent interview form was confirmed to be reliable and valid for the diagnosis of these disorders.16
Child Behavior Check List and teacher report form
The CBCL and the TRF are the most commonly used clinical rating scales designed to determine a broad range of behavioral problems in young individuals. These 113-item questionnaires are completed by the child's parents or teachers and describe behavioral and emotional problems: withdrawal, somatic complaints, anxiousness/depression, social problems, cognitive problems, attention problems, delinquent behavior and aggressive behavior. The raw scores are converted into T-scores (mean, 50 ± 10), which are adjusted for age and sex.
Questionnaire for teachers
Each teacher in charge was requested to provide the following information: (i) class duration (beginning and end time of each class); (ii) class schedule; and (iii) classification of each class as either an ‘in-seat class’ or a ‘not-in-seat class’. During in-seat classes the participants were required to learn quietly while sitting in their own seats; they were expected to maintain their self-control during these classes. In other words, these classes were highly structured and involved reading, writing, mathematics, science, and social studies. Not-in-seat classes did not require the participants to remain seated and included lessons in art, laboratory science, physical education, and special courses.
The actigraphs used in this study were Mini-Motionloggers from Ambulatory Monitoring (Ardsley, NY, USA). The actigraph was a small wristwatch-like device that was worn continuously on the non-dominant wrist. The device utilizes a piezoelectric beam sensor with a fixed sensitivity of 2–3 Hz and is capable of detecting accelerations greater than 0.01 g (Earth's gravity). All data were collected in the zero-crossing mode, which measures the movement frequency by recording a count each time the filtered transducer signal crosses a defined threshold voltage, regardless of whether the voltage increases or decreases; the daytime activity counts were recorded for 1-min epochs. The threshold voltage was set at the default value (mode 18).
Elementary school in Japan
In Japan, elementary schools aim to provide children aged between 6 and 12 years with general compulsory education. Most elementary schools consider a class period to last 40–45 min and schedule a free recess period for 10–20 min following each class. The beginning and end of each class period is announced over a loudspeaker. The school facilities are built in accordance with certain nationwide standards, and desks or seats for the children are assigned according to unified specifications. Moreover, each child is assigned a specific desk and chair, and the children do not need to change classrooms for every class.22,23
Japanese elementary school classes are generally structured. During most classes, around 30–40 children are expected to use the same teaching materials while sitting quietly in their own seats. One teacher is responsible for teaching the children in each classroom. The children are expected to maintain their self-control during the classes. During the free recess period following each class, most children spend their free time in their classroom, with minimal teacher supervision. They are required, however, to stay in the classroom because they are expected to be there for their next class.
The IQs of all the participants were assessed within 6 months of the commencement of the actigraphic monitoring. Although the participants who had been treated with medication were required to stop taking their medication for at least 48 h before the start of actigraphic monitoring, no serious behavioral problems occurred during the study period. Each participant wore the actigraph for 1 week while attending elementary school. Several boys removed their actigraphs during physical education classes because of safety concerns. The teacher in charge later confirmed that the boys had replaced the actigraphs on their non-dominant wrist. The actigraphs were collected at the end of the study period.
The actigraphic data were extracted using operational software (ACT Millennium; Ambulatory Monitoring) and was converted to ASCII text files with one line per epoch (epoch-by-epoch files; these files can be imported into spreadsheets). The first three in-seat classes held in the morning and the free recess periods immediately following these classes were then selected to avoid interference from behavioral differences observed during the lunch/recess periods. Furthermore, for in-seat classes that lasted more than 40 min, we analyzed the 40 min before the beginning of the subsequent free recess period. For recess periods that lasted more than 10 min, only the first 10 min were analyzed.
Calculation of average activity level and standard deviation for two situations
We calculated the 1-min average activity level and the standard deviation in the activity levels for each participant in each of the in-seat classes and free recess periods selected during the investigated period. Next, we added the average and standard deviation for all the classes or the recess periods and calculated the average individual activity levels for each situation. The results were expressed as the average activity level or standard deviation per individual.
All activity data in each situation were compared in the following two ways: (i) actigraphic data for the in-seat classes and free recess periods were compared within groups using a paired t-test; and (ii) the data among groups were compared using a one-way analysis of variance (ANOVA). In addition, the SchefféF-test was used as a post-hoc test for significant ANOVA results. Group differences in age were compared using the Kruskal–Wallis test, and other demographic characteristics were compared using an unpaired t-test or Mann–Whitney U-test. Statistical analysis was performed using SPSS version 13.0, Japanese version (SPSS, Tokyo, Japan), with P < 0.05 considered statistically significant.
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The present study examined whether objective activity levels differed among boys with ADHD, boys with PDD and hyperactivity, and control boys. In addition to using the average activity level as a quantitative measure, the standard deviation in the activity levels was utilized as a measure of the temporal variability in the activity levels. We examined two continuous settings (in-seat classes and free recess periods) to clarify the differences in the activity levels among the groups. During the in-seat classes, the participants were expected to maintain their self-control. During the free recess periods following the in-seat classes they were allowed to do as they pleased, but they were required to stay in their classrooms because they were expected to be there for their next class.
During the free recess periods the average activity level of each group was higher and the standard deviation of each group was smaller than those during the in-seat classes. All groups were affected by the situational shift and changed their activity levels, but the standard deviation of the boys with ADHD was still smaller in the free recess period than that of the boys with PDD and hyperactivity as well as of the controls. Barkley et al. reported that the behavior of children with ADHD might be readily distinguishable from that of typical children if their need for self-control were shifted.24 In the present study the boys with ADHD reflected situational shift more strongly than the control boys and the boys with PDD and hyperactivity, and they had difficulty regulating their activity levels. The smaller variability in the activity levels of the boys with ADHD measured by the actigraph might represent their inhibitory deficits.25
The present results indicated that the average activity level of the boys with PDD and hyperactivity during the free recess periods was significantly lower than that of the boys with ADHD and of the controls. Generally, children with PDD often have difficulty tolerating change and variations in their situations, and this characteristic is different from the situational variability in the symptoms of ADHD. The fact that their average activity levels during the free recess period did not increase to levels similar to those of the boys with ADHD or controls, might reflect their difficulty in tolerating changes in situations.
During the in-seat classes, however, no group differences were seen in the average activity levels and standard deviations. These results suggest that both the boys with ADHD and the boys with PDD and hyperactivity were able to control their movements or behaviors to a level that was nearly the same as the controls during in-seat classes. These findings are consistent with previous results showing no differences in the quantitative activity levels of children with ADHD and normal controls in various settings.3–8 Another possibility is that more situational factors are needed for identifying the differences in the objective activity levels between children with ADHD and without ADHD.
The present findings should be viewed in light of some methodological limitations. The class schedules, class contents, and other factors relating to each participant could not be held constant for all the participants, because this study was performed in a naturalistic setting. One possible way to eliminate this limitation would be to conduct the study in different continuous settings, such as before and after the loosening of the need for self-control in a laboratory classroom.26 The present study indicated that the boys with ADHD exhibited less variability in their activity levels during the free recess periods. Moreover, this study had a small sample size and did not include other ADHD subtypes and PDD without hyperactivity. In order to address these issues, further research is required.
The present results indicate that the observed objective activity levels of the groups may reflect the degree to which the boys are able to tolerate changes in their situations. We conclude that objective activity level measurements may be useful to differentiate hyperactivity in boys with ADHD from hyperactivity in boys with PDD.