Differences between Objective and Subjective Sleep Measures in Children with Attention Deficit Hyperactivity Disorder

Abstract

Study Objectives:

To assess sleep characteristics in children with ADHD through polysomnographic recordings and parental reports of sleep problems.

Methods:

Standard overnight polysomnography evaluation was performed to record sleep in 27 children with ADHD and 26 healthy controls, aged 7 to 12 years. The diagnosis of ADHD was determined by the Korean version of the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version (K-SADS-PL-K). Children taking any medications or in poor health were excluded. All the subjects were assessed with the Children's Sleep Habits Questionnaire which was completed by parents. Overall neurobehavioral functioning was examined using various questionnaires, including the Child Behavioral Checklist (CBCL).

Results:

Based on the findings from the questionnaire, the ADHD group had significantly higher scores on the sleep onset delay (p = 0.027), sleep duration (p = 0.032), night waking (p = 0.006), parasomnias (p = 0.016), daytime sleepiness (p = 0.007), and total sleep disturbance factors (p < 0.001) than children in the control group. However, there were no differences between ADHD and healthy groups on any polysomnographic variables, including sleep structure, arousals, and respiratory disturbances. Reported sleep problems were significantly associated with almost all subscales of CBCL as well as CBCL total score.

Conclusions:

The majority of sleep problems reported by the parents of ADHD children were not verified through the use of polysomnography. These findings raise the possibility that some of the reported sleep problems in ADHD may be related to disturbing behaviors which often characterize children with ADHD.

Citation:

Choi J; Yoon IY; Kim HW; Chung S; Yoo HJ. Differences between objective and subjective sleep measures in children with attention deficit hyperactivity disorder. J Clin Sleep Med 2010;6(6):589-595.

Attention deficit hyperactivity disorder (ADHD) is characterized by symptoms of inattention, overactivity, and impulsivity. It is the most frequently encountered childhood-onset neurodevelopmental disorder in primary care setting and the prevalence rate of the disorder generally ranges from 4% to 12% in community samples of school-aged children.¹ ADHD usually begins before 7 years and leads to problems of behavior and school performance in school-aged children. Symptoms frequently co-occur with other emotional, behavioral, and learning problems including oppositional defiant disorder, conduct disorder, depression, anxiety, and learning disabilities. It is now recognized that ADHD is a chronic condition that will persist over the lifespan.² It is estimated that 40% to 60% of children with ADHD have persistent behavioral problems. Although many of them are no longer diagnosed as ADHD, the prevalence rate of ADHD in adults is reported to be still between 1% and 7.3%.³

The presence of sleep problems in children with ADHD has been the study of considerable research. Sleep problems have been clinically reported in an estimated 25% to 50% of children and adolescents with ADHD.⁴ Previous reports indicate a 2- to 3-fold higher prevalence of sleep problems in children with ADHD compared to controls,⁵ which include difficulty falling asleep, frequent night awakening, increased tiredness upon waking,⁶ and longer sleep latency after waking.⁷ Also, ADHD children were reported to show more sleep related breathing disorder, enuresis, sleep talking, bruxism,⁸ and parasomnias such as night terrors and sleepwalking compared to normal controls.⁹ Parents of children with ADHD have reported that their children have more sleep problems.^7,10,11 However, studies using objective measures such as polysomnography and actigraphy have not shown consistent evidence of differences in sleep between ADHD and normal samples. Some polysomnographic studies have found that there were no differences in total sleep time, percentages of REM sleep, and REM latency between the ADHD and the control group.^12–14 Other studies have yielded varied and often contradictory findings, such as significant short sleep duration, significant decrease in REM sleep, or significant decrease in REM latency in ADHD children versus controls.^9,15,16 In addition, although the presence of comorbid psychiatric problems might mediate the observed associations between sleep characteristics and ADHD,^17,18 previous studies have failed to control these problems.

BRIEF SUMMARY

Current Knowledge/Study Rationale: In investigation of sleep problems in children with ADHD, studies using objective sleep measures have shown inconsistent findings compared to researches with subjective reports. In addition, psychiatric comorbidities frequently observed in children with ADHD, were not well controlled in previous studies on sleep problems in ADHD children.

Study Impact: The presence of sleep problems in children with ADHD could be explained in relation with psychopathology instead of primary sleep disorders. Future studies on sleep problems of ADHD children should comprise subjective sleep reports and ADHD symptomatology as well as objective sleep measures.

The purpose of the current study was to examine objective sleep characteristics and reported sleep problems in children with ADHD and normal controls without ADHD, excluding roles of psychiatric comorbidities. Also, we intended to find factors explaining discrepancies between objective and subjective sleep measures in patients with ADHD.

METHODS

Participants

Subjects were recruited at the Department of Child Psychiatry of Seoul National University Bundang Hospital. All children in the ADHD group were recruited before starting any medication to treat their ADHD symptoms. The diagnosis of ADHD was based on the criteria from the Diagnostic and Statistical Manual, 4th edition (DSM-IV) according to the Korean version of the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version (K-SADS-PL-K).

In addition, in order to achieve consensus regarding ADHD symptoms, the Clinical Global Impression-Severity (CGI-S) was completed by clinicians. Children with CGI-S of moderately ill or greater severity (rating ≥ 4) were included in the study. Normal control children were recruited from schools in Seongnam-si through advertisements. Exclusion criteria for participation were as follows: IQ < 80 on the Korean-Wechsler Intelligence Scale for Children, 3rd edition (K-WISC-III), brain injury, past and/or current history of developmental disorder including autism spectrum disorder, neurological disorder (e.g., seizure), significant comorbid medical illness, or presence of comorbid psychiatric diagnosis on the K-SADS-PL-K. We received written informed consents from the parents of all the children who took part in the study, and the institutional review board of the Seoul National University Bundang Hospital approved this study.

Neurobehavioral Assessment

Psychiatric Diagnosis

The diagnoses of ADHD and comorbid psychiatric disorders were determined by the K-SADS-PL-K. The Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version (SADS-PL-K) is a well-validated semi-structured diagnostic interview designed to assess current and past episodes of psychopathology in children and adolescents according to DSM-IV criteria.¹⁹ The Korean version of the SADS-PL-K (K-SADS-PL-K) was translated and validated in Korean by Kim et al.²⁰

The Wechsler Intelligence Scale for Children-III (WISC-III)²¹

The WISC-III comprises the verbal and the performance scale, which are computed for individual subtest scores, the verbal IQ score, the performance IQ score, and the full-scale IQ score. The full-scale IQ score has a mean of 100 and a standard deviation of 15.

Behavioral Assessment

Overall behavioral and cognitive functioning were examined using the Korean version of Child Behavioral Checklist (K-CBCL),²² a 113-item parental questionnaire assessing behavioral and emotional problems grouped into 8 subscales and 3 global scales. At level of global scores, externalizing and internalizing symptoms can be differentiated. Parents provided information for 20 competence items covering their child's activities, social relations, and school performance. Additionally, parents completed the Korean version of ADHD Rating Scale (K-ARS),²³ Children's Depression Inventory (CDI),²⁴ State-Trait Anxiety Inventory (STAI),²⁵ and Yale Global Tic Severity Scale (YGTSS).²⁶ The Korean versions of all the instruments used in this study are known to have good validity and reliability.

Children's Sleep Habits Questionnaire

Sleep related behaviors were evaluated using the Children's Sleep Habits Questionnaire (CSHQ).²⁷ The CSHQ is a 33-item questionnaire and includes items relating to a number of key sleep domains conceptually grouped into 8 subscales reflecting: (1) bedtime resistance; (2) sleep onset delay; (3) sleep duration; (4) sleep anxiety; (5) night wakings; (6) parasomnias; (7) sleep disordered breathing; (8) daytime sleepiness. Items were rated on a 3-point scale ranging from “usually” (5 to 7 times/week) to “sometimes” (2 to 4 times/week) and “never/rarely” (zero to one time/week). Total sleep disturbance score includes all items of the 8 subscales. Higher scores are indicative of more disturbed sleep.

Polysomnography

Overnight polysomnography was performed on all the participants by using an Embla N 7000 recording system (Embla; Reykjavik, Iceland) and standard electrodes and sensors. Electroencephalography electrodes were applied at C3/A2, O1/A2, and O2/A1, and 2 electrooculography (EOG) electrodes were applied at the sides of both eyes to record horizontal and vertical eye movements. Submental electromyography (EMG) electrodes were applied at submentalis muscle and the EMGs of both anterior tibialis muscles recorded limb movements during sleep. Strain gauges were used for recording chest and abdominal respiratory movements, and nasal pressure cannulas were used to record airflow. Arterial oxygen saturation was measured using pulse oximeters applied on index fingers. Based on the criteria of Rechtschaffen and Kales,²⁸ we scored every epoch of 30-sec NPSG. Apnea and hypopnea for children were scored according to the scoring criteria consistent with current published AASM standards.²⁹ Apneas were defined as > 90% decrement of airflow for ≥ 2 breaths on the nasal pressure cannula signal. Hypopnea were defined as > 50% decrease in airflow on the nasal pressure cannula signal for ≥ 2 breaths, accompanied by an arousal, awakening, or > 3% desaturation. Apnea-hypopnea index (AHI) was defined as the total number of apnea and hypopnea events per hour of sleep. An AHI ≥ 1 was considered abnormal to define sleep disordered breathing in this study.

Data Analysis

SPSS version 15.0 was used for statistical analysis. Different demographics, intellectual and psychiatric characteristics, CSHQ variables, and polysomnographic parameters were compared across groups using either χ² analysis or independent t-test. To explore whether baseline neurobehavioral assessments might be associated with variables of sleep characteristics, correlation analyses were performed. All tests were 2-tailed, with statistical significance defined as p < 0.05.

RESULTS

Study Population and Neurobehavioral Assessments

A total of 27 children with ADHD and 26 healthy children were included in this analysis. We present demographic clinical characteristics of the ADHD children and the controls in the Table 1. The mean age was 9.0 ± 2.1 years for the ADHD group and 8.4 ± 1.5 years for the control group. Among the participants, 88.9% of the ADHD children and 88.5% of the control subjects were boys. The groups did not differ in their gender, age, or BMI distribution. Two-thirds of the ADHD children were diagnosed as having ADHD-combined type (18 subjects, 66.7%), followed by predominantly inattentive type (7 subjects, 25.9%) and predominantly hyperactive/impulsive type (2 subjects, 7.4%). Based on CBCL, significant differences were observed in the neuropsychological characteristics. Children in the ADHD group showed higher scores on internalizing, externalizing, and total scores than controls except on the sexual problem subscale (Table 2). In addition, children in the ADHD group scored higher than controls on the state anxiety of STAI, children's depression inventory (CDI) scale, as well as mood disorder questionnaire (MDQ), although they did not show clinical evidence of any psychiatric disorders at baseline assessments except ADHD. We did not find any significant differences between the 2 groups in trait anxiety of STAI (p = 0.246) and YGTSS (p = 0.327).

Table 1.

Demographic and clinical characteristics of children with ADHD and controls

Characteristic	ADHD (n = 27)	Controls (n = 26)	p
Age (yr), mean (SD)	8.97 (2.1)	8.36 (1.5)	0.23
Sex, n (%)			0.96
Boys	24 (88.9)	23 (88.5)
Girls	3 (11.1)	3 (11.5)
Weight (kg), mean (SD)	29.1 (7.7)	30.5 (8.4)	0.55
Height (cm), mean (SD)	130.0 (10.4)	132.2 (9.5)	0.44
BMI	17.0 (3.0)	17.2 (2.8)	0.85
ADHD diagnosis, n (%)	27
Predominantly inattentive	7 (25.9)
Predominantly hyperactive/impulsive	2 (7.4)
Combined type	18 (66.7)
Diagnosis of RLS, n (%)	2 (7.4)	1 (3.8)	0.58
IQ, mean (SD)	105.2 (11.1)	109.4 (11.6)	0.19

ADHD, attention deficit hyperactivity disorder; RLS, restless legs syndrome; IQ, intelligent quotient; BMI, body mass index

Table 2.

Neurobehavioral assessments of children with ADHD and controls

Characteristic	ADHD (n = 27)	Controls (n = 26)	p
CBCL T score	59.65 (6.8)	50.08 (0.4)	< 0.001
Withdrawn	60.81 (13.2)	50.92 (2.2)	0.001
Somatic complaints	55.23 (5.9)	50.56 (1.7)	0.001
Anxious/depressed	57.42 (6.6)	51.00 (2.3)	< 0.001
Social problems	60.54 (7.5)	50.32 (1.1)	< 0.001
Thought problems	57.19 (8.3)	50.28 (1.4)	< 0.001
Attention problems	61.04 (6.7)	50.00 (0.0)	< 0.001
Conduct problems	56.85 (6.7)	50.60 (1.7)	< 0.001
Aggressive behavior	59.73 (8.1)	50.36 (1.0)	< 0.001
Sexual problems	54.42 (8.4)	51.68 (4.1)	0.142
Affective problems	53.73 (5.2)	50.00 (0.0)	0.001
Internalizing score	57.88 (6.6)	50.40 (1.2)	< 0.001
Externalizing score	59.31 (7.2)	50.32 (0.7)	< 0.001
STAI score
Trait-anxiety score	26.36 (9.5)	23.80 (5.3)	0.25
State-anxiety score	31.00 (7.5)	26.00 (4.5)	0.006
CDI score	13.08 (6.8)	5.20 (5.8)	< 0.001
MDQ			< 0.001
Mild	13 (50.0)	24 (96.0)
Moderate	8 (30.8)	1 (4.0)
Severe	5 (19.2)	0
YGTSS score	0.38 (2.0)	0.0 (0.0)	0.327

CBCL, Child Behavioral Checklist; MDQ, Mood Disorder Questionnaire; CDI, Children's Depression Inventory; STAI, State-Trait Anxiety Inventory; YGTSS, Yale Global Tic Severity Scale

Reported Sleep Problems: The Child Sleep Questionnaire

Table 3 displays the sleep patterns and 8 sleep parameters on the CSHQ. The 2 groups did not differ in bedtime, wake-up time, or sleep duration on a nightly basis.

Table 3.

Reported sleep patterns and sleep problems, based on CSHQ

	ADHD (n = 27) mean ± SD	Controls (n = 26) mean ± SD	p
Sleep patterns
Bedtime, h	22.10 ± 0.63	22.40 ± 0.70	0.105
Morning wakeup, h	7.34 ± 0.47	7.55 ± 0.57	0.151
Sleep duration, h	8.77 ± 0.82	8.98 ± 0.90	0.368
CSHQ subscales
Bedtime resistance	10.44 ± 3.25	9.58 ± 2.97	0.316
Sleep onset delay	1.48 ± 0.75	1.12 ± 0.33	0.027
Sleep duration	4.30 ± 1.56	3.54 ± 0.81	0.032
Sleep anxiety	6.33 ± 2.02	6.00 ± 2.08	0.556
Night awakenings	4.15 ± 1.54	3.23 ± 0.51	0.006
Parasomnias	9.67 ± 1.64	8.58 ± 1.53	0.016
Sleep disordered breathing	4.00 ± 1.49	3.46 ± 0.99	0.129
Daytime sleepiness	16.81 ± 3.98	13.85 ± 3.78	0.007
Total sleep disturbance score	53.89 ± 7.51	46.08 ± 7.07	< 0.001

CSHQ, Children's Sleep Habits Questionnaire

However, a significant difference between the groups was found on 5 of the 8 sleep parameters and the total sleep disturbance score. The ADHD group was found to have more difficulty with sleep onset (p = 0.027), more inadequate sleep duration (p = 0.032), more night awakenings (p = 0.006), more daytime sleepiness (p = 0.007), and more parasomnias (p = 0.016). Also, total score of sleep disturbance was much higher in the ADHD group than the controls (p < 0.001). However, the 2 groups did not differ in the bedtime resistance, sleep anxiety, or sleep disordered breathing. In addition, we diagnosed RLS in children who fulfilled all 4 diagnostic criteria of the International RLS Group and who complained of discomfort on the legs in their own words. Two subjects among children with ADHD and one subject among healthy controls could be diagnosed as having RLS, which did not reach clinical significance (p = 0.575).

Objective Measures of Sleep: Polysomnography

In Table 4, we present the polysomnographic sleep measures of the ADHD children and controls. There were no significant differences between ADHD and healthy groups in any of the sleep parameters including sleep structure, spontaneous arousal index, snoring times, respiratory disturbances, or periodic limb movement (PLM) index.

Table 4.

Polysomnographic sleep measures of ADHD children and controls

	ADHD (n = 27) mean ± SD	Controls (n = 26) mean ± SD	p
Time in bed (min)	408.44 ± 37.48	399.11 ± 35.32	0.356
Sleep period time (min)	388.40 ± 42.20	378.02 ± 44.48	0.387
Wake time (min)	18.54 ± 14.92	26.20 ± 26.20	0.200
Total sleep time (min)	369.86 ± 40.77	351.82 ± 46.80	0.140
Sleep onset latency (min)	20.03 ± 25.52	21.10 ± 31.36	0.892
REM latency (min)	160.04 ± 67.07	152.19 ± 66.70	0.671
Sleep efficiency (%)	90.85 ± 6.91	89.39 ± 8.09	0.482
Sleep stage, min (% of SPT)
Stage 1	19.5 ± 15.2 (5.1)	23.6 ± 10.8 (6.2)	0.27 (0.22)
Stage 2	157.9 ± 37.9 (40.9)	148.5 ± 48.9 (38.8)	0.43 (0.48)
SWS	132.23 ± 38.66 (34.05)	122.45 ± 32.54 (33.02)	0.33 (0.70)
Stage REM	60.2 ± 26.9 (15.3)	57.3 ± 22.1 (15.1)	0.68 (0.89)
PLM index	0.04 ± 0.08	0.05 ± 0.08	0.911
SAS (%)	44.4	38.5	0.435
Primary snorer (%)	48.1	57.7	0.337
AHI (/h)	0.90 ± 0.87	1.84 ± 4.59*	0.299
AHI during REM sleep (/h)	1.20 ± 1.36	4.09 ± 11.48*	0.214
Spontaneous arousal index	4.58 ± 1.86	4.74 ± 1.95	0.760
Respiratory arousal index	0.56 ± 0.78	1.17 ± 3.10	0.330
Snoring time (min)	12.60 ± 25.72	13.32 ± 43.71	0.942
SpO2 (%)	97.84 ± 0.59	97.82 ± 0.74	0.891

SPT, sleep period time; SWS, slow wave sleep; PLM, periodic limb movement; AHI, apnea hypopnea index; TST, total sleep time; SAS, sleep apnea syndrome.

^*Because of one outlier, control group showed large SD. After excluding the outlier, there was still no difference between two groups.

Correlation between Neurobehavioral Problems and Reported Sleep Problems

We conducted correlation analyses to explore the relationships between neurobehavioral problems and variables of CSHQ. In these analyses, we included only 6 variables of CSHQ which were found to differ between the groups. Table 5 shows the correlation coefficient and statistical significance between reported sleep problems and neurobehavioral problems. Sleep onset delay and sleep duration were significantly correlated with social and attention problems. Night awaking had positive correlation with almost all variables of CBCL. Also, daytime sleepiness was highly correlated with social and attention problems and aggressiveness. Parasomnia had positive correlations with withdrawn and anxious/depressed. Total sleep disturbance was significantly associated with almost all subscales of CBCL as well as CBCL total behavioral problems score.

Table 5.

Correlation between reported sleep problems and neurobehavioral problems in children with ADHD (N = 27)

	Sleep onset delay	Sleep duration	Night awaking	Parasomnia	Daytime sleepiness	Total sleep disturbance
Withdrawn	0.199	0.143	0.165	0.286a	0.251	0.290a
Somatic complaints	0.268	0.100	0.243	0.228	0.078	0.331a
Anxious/depressed	0.130	0.098	0.421b	0.292a	0.200	0.366b
Social problems	0.294a	0.284a	0.302a	0.194	0.438b	0.445b
Attention problems	0.289a	0.295a	0.282a	0.075	0.459b	0.449b
Conduct problems	0.097	0.082	0.135	0.194	0.346a	0.260
Aggressive behavior	0.206	0.127	0.396a	0.81	0.413b	0.376b
Internalizing score	0.206	0.144	0.416b	0.251	0.230	0.016
Externalizing score	0.202	0.121	0.370b	0.191	0.421b	0.374b
CBCL T score	0.255	0.155	0.399b	0.230	0.361b	0.429b

CSHQ, Children's Sleep Habits Questionnaire;

^ap-value < 0.05;

^bp-value < 0.01.

DISCUSSION

The results obtained from the application of the sleep questionnaire corroborated the clinical impression that children with ADHD were poor sleepers. However, the majority of sleep problems which were reported by the parents of ADHD children were not verified through the use of polysomnography. The disparity between subjective and objective findings could be supported by the report of Corkum et al.⁶ Corkum and colleagues hypothesized that the parental report of sleep disturbances of children with ADHD may be related to the difficulties in managing problematic behaviors rather than primary sleep disorders in ADHD. Parents of children with ADHD complain of hyperactive and aggressive behaviors that occur all day long. The continuation of these behaviors to bedtime is the most likely explanation for the higher probability that parents of children with ADHD may overreport sleep problems. Although none of our participants were diagnosed as having comorbid psychiatric disorder, the eight subscale and three global scores of the CBCL, State-Anxiety score of the STAI, and CDI score were significantly higher in children with ADHD than control children. Children with ADHD are known to experience anxiety, mood, and behavioral symptoms which do not meet the DSM-IV diagnostic threshold.^30,31 Because depression and anxiety symptoms are generally associated with sleep problems in previous studies³² and the current one, subthreshold psychopathology could contribute to the parent-reported sleep disturbances. Thus, sleep problems of ADHD children may be related to core symptoms of ADHD and associated psychopathology.

We did not find evidence of an association between ADHD and motor movements during sleep, which has been reported by previous studies. Most of researches employing actigraphy found that ADHD children moved more frequently during sleep.^33–35 Picchietti and Walters discovered that 91% of children with periodic limb movement disorder (PLMD) in their clinic had a diagnosis of ADHD and found an increase in PLM index in ADHD children based on polysomnography.³⁶ However, Chervin and Hedger found no association between PLMD and inattention/hyperactivity in children based on polysomnography.³⁷ The disparity in these findings is difficult to reconcile, and further indicates the need for additional research on the significance of PLMD in children with ADHD. In this study, two subjects among children with ADHD and one subject among healthy controls could be diagnosed as having RLS, which did not reach clinical significance. After reviewing the literature, Cortese et al. concluded that up to 44% of children with ADHD have RLS or RLS symptoms.³⁸ Silvestri et al. also found a high percentage of RLS (26.1%) in their ADHD sample in the recent study.³⁹ These data suggest that a common dopaminergic disruption is likely to be the potential mechanism underlying the association between RLS and ADHD. The low ferritin level in ADHD children could further support the hypotheses. In contrast, we did not find any difference in iron and ferritin in our study (not reported) and Gamaldo et al. found no association between RLS and ADHD symptoms.⁴⁰ Therefore, the association between RLS and ADHD is inapparent and should be considered prudently.Earlier studies showed that children with ADHD had a significantly higher AHI than controls,^12,41 but there was no association between ADHD and sleep disordered breathing in the study. Chervin et al. pointed out that mild SDB may be particularly common in children with ADHD and suggested that the effects of hypoxia or sleep fragmentation associated with apnea and hypopneas might explain the cause-and-effect relationship between SDB and symptoms of ADHD.⁴² In their 4-year prospective study, Chervin et al. reported that snoring and symptoms of SDB were strong risk factors for future development or exacerbation of symptoms of hyperactivity.⁴³ However, the cause-and-effect relationship between SDB and ADHD is not certain, because they did not perform any strict evaluations of ADHD. Other studies reported that there was no significant difference in AHI between children with ADHD and controls.^44,45 In a recent study, Gruber et al. also reported that no significant between-group differences were observed in sleep disordered breathing, although they did not use nasal cannulas.¹⁶ In this study, we overcame their limitation, using nasal cannulas to more accurately detect obstructive apneas and we could confirm no association between ADHD and SDB.

There are several limitations of the current study. First, polysomnography was conducted for only one night. Sleeping in an unfamiliar environment may not represent the usual sleep patterns in ADHD children and normal controls. Besides, sleep parameters could be more influenced by the first-night effect in children with ADHD who are more sensitive to changes in the environment than controls. At least two nights of PSG can be more desirable in evaluating sleep characteristics. Also, children in this study got only 6 hours sleep on the night of the NPSG compared to 9 hours of sleep at home, and the short sleep time on the NPSG night could skew the results. However, considering that all the children had more than three REM-NREM cycles and there was no difference in sleep time between children with ADHD and normal controls, the skewness of the results because of the short sleep time might be minimized. Second, we did not assess for objective measures of daytime sleepiness such as multiple sleep latency test (MSLT), thereby restricting our ability to interpret increased parental reports of excessive daytime sleepiness in children with ADHD compared with healthy children. Third, the current study only assessed a modest number of participants, mainly boys. Therefore the result is limited in the generalization of the findings even though ADHD is diagnosed nine times more frequently in boys than girls.^46,47 Lastly, although this study revealed a relationship between psychopathology and reported sleep problems in children with ADHD from correlation analysis, correlation coefficients were small and the relationship was modest. Further studies with large sample sizes are needed to confirm the association between psychopathology and reported sleep problems in ADHD children. Nonetheless, the current study sought to address some of the methodological weakness of previous research. We used both subjective sleep questionnaires and objective polysomnography to get comprehensive understanding of the sleep characteristics of children with ADHD. We also excluded children with comorbid diagnoses to avoid any factors confounding the relationship between sleep problems and ADHD symptomatology.

In conclusion, we showed that parental reports demonstrated increased frequencies of sleep problems among children with ADHD. However, we did not find any differences in sleep structure, sleep disordered breathing, or periodic limb movements between children with ADHD and healthy children based on polysomnography. These findings suggest that sleep disturbances in ADHD may be more related to ADHD symptoms rather than primary sleep disorders.

DISCLOSURE STATEMENT

This study was sponsored by Janssen. The authors received no income from the company and have no other financial conflicts of interest to report.