Prevalence of Anxiety Disorders in Hong Kong Chinese Children With ADHD

Abstract

Objective: This study examined the prevalence and correlates of anxiety disorders in Chinese children with ADHD. Method: Overall, 120 children with ADHD aged 6 to 12 years were recruited, and the parent version of computerized Diagnostic Interview Schedule for Children–Version 4 was administrated to their primary caretakers. Results: The prevalence rate of anxiety disorders was 27.5%, which is consistent with the reports of previous Asian and Western studies. Among the children with ADHD and anxiety disorders, more than 50% of them also had comorbid oppositional defiant disorder or conduct disorder (ODD/CD), which yielded an adjusted odds ratio of 3.0 in multivariable analysis for anxiety disorder, with comorbid ODD/CD. In addition, anxiety disorders were positively associated with inattention symptoms in children with both disorders. Conclusion: Clinicians should perform screening and careful assessment for anxiety symptoms in children with ADHD, particularly those suffering from comorbid ODD/CD.

Keywords

ADHD anxiety comorbidity

Introduction

ADHD is a heterogeneous clinical disorder. Comorbidities with both externalizing and internalizing disorders are often observed with ADHD. Anxiety symptoms or disorders in children with ADHD are often overlooked by clinicians or caregivers. However, the anxiety results in additional psychosocial deficits in children with ADHD. Several studies have revealed that children with both disorders exhibit substantially reduced quality of life, poorer overall behavior, and daily functioning (Mikami, Ransone, & Calhoun, 2011; Sciberras et al., 2014). Studies have reported considerably high comorbidity rates of anxiety disorders in children with ADHD since the early 1980s (Anderson, Williams, McGee, & Silva, 1987; Lahey, Schaughency, Hynd, Carlson, & Nieves, 1987). The National Institute of Mental Health Collaborative Multisite Multimodal Treatment of Children with ADHD (MTA) study demonstrated that approximately 33.5% of 579 elementary school aged children with combined subtype of ADHD satisfied the criteria of the revised third edition of the Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; DSM-III-R; American Psychiatric Association [APA], 1987) for an anxiety disorder excluding simple phobia (March et al., 2000). In addition, Tsang et al. (2012) reported that 31% of children with ADHD had anxiety disorders defined by DSM (4th ed.; DSM-IV; APA, 1994) criteria. Overall, reviews throughout the decades concluded that anxiety disorders are present in approximately 25% of children and adolescents with any subtypes of ADHD (Biederman, Newcorn, & Sprich, 1991; Jarrett & Ollendick, 2008; Jensen, Martin, & Cantwell, 1997; Schatz & Rostain, 2006). This was significantly higher than the prevalence of anxiety disorders in community, which was reported as 5% to 15% in various Asian and Western studies (Canino et al., 2004; Gau, Chong, Chen, & Cheng, 2005; P. W. Leung et al., 2008).

Thus, substantive underlying reasons must be considered for the high comorbidity rates of ADHD and anxiety disorders. Numerous studies have presented possible explanations to support the typically high covariation observed between internalizing and externalizing disorders in general (Angold, Costello, & Erkanli, 1999; Jarrett & Ollendick, 2008; Lilienfeld, 2003). Among these, certain studies have reported consistent findings to support the explanatory pathway that ADHD and anxiety may be influenced by common factors or certain third variables (e.g., oppositional defiant disorder [ODD], conduct disorder [CD], and temperamental factors). Baldwin and Dadds (2008) and Keiley, Lofthouse, Bates, Dodge, and Pettit (2003) observed that an irritable temperament and disruptive behaviors were associated with the covarying phenomenon of ADHD and anxiety symptoms. March et al. (2000) discovered that children with ADHD who present with CDs exhibit a significantly higher risk of anxiety disorders. Jensen et al. (1997) advocated another explanation that this particular group of anxious ADHD children should be considered as a distinct clinical ADHD subtype. The strongest evidence has been deduced from the different treatment responses in children with ADHD and anxiety disorders (Diamond, Tannock, & Schachar, 1999; Jensen et al., 2001; Pliszka, 1989; Tannock, Ickowicz, & Schachar, 1995). The MTA study revealed that children with ADHD and anxiety were more likely to benefit from a combination of medication and psychosocial treatment than were those with ADHD without anxiety (Jensen et al., 2001). However, limited evidence is available to support that ADHD and comorbid anxiety can be considered as a diagnostically meaningful subtype or rather a separate disorder. Considering the emerging importance of psychosocial treatment, several studies have been focusing on the family environment of children with both ADHD and anxiety disorders, which reported a strong association between parental anxiety and children anxiety (Gerdes et al., 2007; Kepley & Ostrander, 2007; Pfiffner & McBurnett, 2006).

Compared with Western countries, only a few studies in Asia have focused on general comorbidities observed in children with ADHD. Most of these studies had not particularly investigated the comorbid states of ADHD and anxiety (Byun et al., 2006; Gau et al., 2005; Gau et al., 2010; Takahashi et al., 2007; Yang, Jong, Hsu, & Tsai, 2007). In addition, the findings reported among these studies were inconsistent. A study in Japan investigated 41 clinical samples by administrating a semi-structured interview, the Japanese Kiddie-Schedule for Affective Disorders and Schizophrenia for School-Aged Children–Present and Lifetime version (K-SADS-PL-J). This small scale study indicated that 51% of children with ADHD exhibited anxiety disorders, with simple phobia being the most prevalent anxiety disorder (Takahashi et al., 2007). A South Korean study using the same semi-structured interview reported that 33.5% of 105 clinical participants with ADHD exhibited anxiety disorders; moreover, separation anxiety was the most common anxiety disorder and only 7.6% of the participants had simple phobia. Based on our research, the only available studies on Chinese participants were from Taiwan. Yang et al. (2007) observed a surprisingly low prevalence (7/182 participants) of anxiety disorders among children with ADHD using the Children’s Interview for Psychiatric Syndromes and its parent version (ChIPS and P-ChIPS, respectively), but indicated a significantly higher prevalence of anxiety disorder in the inattention subtype of ADHD. However, these results varied from those of a more recent Taiwanese case–control study, which examined psychiatric comorbidity among 296 children and adolescents with ADHD compared with 185 school controls, which revealed that patients with ADHD exhibited higher risks of anxiety disorders (prevalence rate = 31.7%), particularly regarding specific phobia, than did the controls. Nevertheless, the diagnoses were confirmed based on unstructured clinical assessments only (Gau et al., 2010). Another Taiwanese study conducted by Tai, Gau, Gau, and Chiu (2012) compared 2,385 children with ADHD with a control group over a 4-year observation period, and they reported a significant prediction of ADHD to anxiety disorders after controlling for other psychiatric comorbidities. Using the International Classification of Diseases–Ninth Revision, Clinical Modification (ICD-9-CM), a total of 421 children with ADHD (17.7%) developed new diagnosis of anxiety disorder. However, the diagnoses of ADHD and anxiety disorders could not be validated because all the diagnoses were determined by a retrospective retrieval and review of case records. Essential information such as symptom severity, education, or socioeconomic status was lacking.

In conclusion, the prevalence of anxiety disorder in children with ADHD is significant. Although the nature of the anxiety and the underlying substantive reasons remain uncertain, this comorbidity brings additional burdens to the lives of children, suggesting different treatment outcomes, and perhaps providing a major direction in clinical practice. Nevertheless, to date, most Asian studies have reported contradicting results regarding both the prevalence and the pattern of anxiety in children with ADHD, not least because of methodological shortcomings, but possibly also because of cultural differences. Data on Chinese children in Hong Kong are unavailable. Therefore, identifying the prevalence of this problem and alerting clinicians to the profile of this group of children is critical.

Study Objectives and Hypothesis

The present study aimed to examine the prevalence and correlates of anxiety disorders among Chinese children with ADHD in Hong Kong. The study results were compared with those of a local epidemiological study focused on children in community with the same diagnostic criteria as used in our study (P. W. Leung et al., 2008). The literature findings suggest that the prevalence of anxiety disorders in children with ADHD is higher than that in the general population. In addition, we determine whether the anxiety disorders observed in children with ADHD were associated with comorbid ODD/CD and parental internalizing psychopathologies.

Materials and Method

Participants and Procedure

All consecutive referrals for suspected ADHD or behavioral problems to the child psychiatry outpatient clinic at the Alice Ho Miu Ling Nethersole Hospital from July 2011 to March 2012 were enrolled. This hospital serves the New Territories East area of Hong Kong, with a population of 1.3 million, which is approximately one sixth of the local population (Census and Statistics Department, 2011a). These children were seen by child psychiatrists in routine consultations and included when a working diagnosis of ADHD was achieved. All participants were aged 6 to 12 years and studied at local elementary schools—children of this age group are typically the first ones to present at our clinic with suspected ADHD. In addition, this specific age group falls between the phases of early childhood to preadolescence, which includes its own challenges and anxieties. Children who were already on psychiatric medications (including those for ADHD), suffering from mental retardation, autistic spectrum disorder, or any severe medical illness, which required long-term medication were excluded. By implementing these stringent inclusion and exclusion criteria, a homogeneous group of children with ADHD was identified, which enabled examining the natural covariations of ADHD and anxiety disorders.

Ethical approval was obtained from the relevant institutional boards for human studies. Participants were recruited only when their parents or caregivers provided written consent in Chinese. Subsequently, arrangements were made for the principal investigators to interview the parents by using the parent version of the computerized Diagnostic Interview Schedule for Children–Version 4 (DISC-IV), administering modules on anxiety disorders and disruptive behavior disorders (Ho et al., 2005). ADHD was further confirmed using the DISC-IV. The interview length considerably varied based on the number and severity of the problems reported. Typically, it took around 1.5 to 2 hr. Both parental and family demographic data were collected, and both biological parents were required to complete the Hospital Anxiety Depression Scale (HADS) questionnaires (C. M. Leung, Ho, Kan, Hung, & Chen, 1993; C. M. Leung, Wing, Kwong, Lo, & Shum, 1999).

Definition of Anxiety Disorders

In the present study, the recruited children were divided into two groups: ADHD with anxiety disorder (ADHD + ANX) and ADHD without anxiety disorder (ADHD-only). The presence of anxiety disorder was defined as the confirmation of any anxiety disorder satisfying the DSM-IV symptom and impairment criteria.

Measures

The parent version of computerized DISC-IV is a respondent-based structured interview schedule, upon a 12-month time frame, thus providing point prevalence rates for the disorders investigated in the present study. It helps to rule out clinician bias or interviewer expectancies as possible explanations of the observed comorbidity rates. Furthermore, it excludes the problem of inter-rater disagreement. An extensive literature review supports the reliability and validity of its various versions, including Cantonese version for use in Hong Kong (Ho et al., 2005; Shaffer, Fisher, Lucas, Dulcan, & Schwab-Stone, 2000). DISC-IV is the only available diagnostic tool that generates categorical diagnoses applicable in the local clinical settings. In addition, it rates the frequency and severity of symptoms, along with the functional impairment addressed to each disorder. In this study, the recommendations of the DISC Development Group (2001, personal communication) were followed, wherein an impairment score of 3, equivalent to one severe or at least two intermediate impairments in the six domains of daily function, was considered clinically significant.

HADS was designed with seven items each to measure the presence and severity of anxiety and depression. Throughout the scale, the items were alternated for anxiety and depression. Participants were requested to complete the scale by rating how they felt regarding the symptoms they had experienced in the preceding week using a 4-point scale, ranging from 0 to 3 (0 = absence of symptoms to 3 = severe symptoms). HADS has exhibited favorable performance in assessing the symptom severity and identifying the clinical cases of anxiety disorders and depression in somatic, psychiatric, and primary care patients as well as in the general population (Bjelland, Dahl, Haug, & Neckelmann, 2002; Olsson, Mykletun, & Dahl, 2005). It has been translated into a local Cantonese version. It exhibits good internal consistency (.86) and external validity (area under the curve [AUC] = 0.83), with a favorable sensitivity (0.8) and specificity (0.8) for screening psychiatric disorders (C. M. Leung et al., 1993; C. M. Leung et al., 1999).

Statistical Methods

Data analyses were performed using the SPSS 20.0 statistical software (SPSS Inc., Chicago, IL, USA). The differences in the demographic information, clinical profiles including ADHD subtypes and ODD/CD comorbid state, and parental anxiety depression levels between the ADHD-only and the ADHD + ANX groups were compared using the Student’s t test and chi-square test or Fisher’s exact test. Logistic regressions were further conducted to determine the relationship between anxiety disorders (dependent variable), ADHD symptoms, and the other variables, which had revealed significant differences (p < .1) in univariate analysis. Age and sex were controlled in the regression analyses. All candidate variables were included into the model by using the backward method. All statistical tests were two-tailed and p < .05 was considered significant. The results were expressed as mean ± standard deviation where appropriate.

Results

Overall, 160 parents were approached, but only 128 provided written consent. The sample finally comprised 120 children who satisfied the DSM-IV symptom and impairment criteria of ADHD. Eight children were excluded because of lack of any clinically significant impairment. The mean age of the children was 8.4 ± 1.7 years. The sample comprised 90 boys (75%, mean age at 8.3 ± 1.6 years) and 30 girls (25%, mean age at 8.7 ± 1.9 years). Among these, 67 (55.8%) children were diagnosed with the combined subtype of ADHD, 44 (36.7%) with the inattention subtype, and only 9 (7.5%) with the hyperactivity subtype. The interview was administered to the child’s primary caregivers, including the father (1.6%), mother (95.3%), and grandparents (3.1%). Of the 32 parents who refused to participate and were excluded, no significant differences were observed in the factors of age and sex in the refusal group compared with the sample group.

A total of 27.5% of children with ADHD exhibited comorbid anxiety disorders. The most prevalent anxiety disorder was specific phobia, followed by separation anxiety disorder and social phobia. Overall, 52% of all the anxious participants exhibited more than one anxiety disorder (Table 1).

Table 1.

Prevalence of Elevated Anxiety Symptoms and Fully Developed Anxiety Disorders.

Anxiety disorder	Elevated anxiety symptoms (symptom criteria only)	Anxiety disorders (symptom and impairment criteria)
Specific phobia/simple phobia	57	23
Separation anxiety disorder	20	14
Social phobia disorder	16	10
Generalized anxiety disorder	4	3
Obsessive compulsive disorder	2	2
Panic disorder	1	1
Selective mutism	1	1
Total (some cases have more than one anxiety disorder)	101	54
M number of anxiety disorders among all participants	0.75 ± 0.91	0.42 ± 0.80
M number of anxiety disorders among anxious participants	1.53 ± 0.70	1.61 ± 0.75

Comparison Between Children With ADHD + ANX and ADHD-Only

Demographic data

Only maternal age was found to be statistically different, whereas all other characteristics were insignificant. The mean maternal age of children in the ADHD + ANX group was higher than that of children in the ADHD-only group (p < .05, Tables 2, 3, and 5).

Table 2.

Comparison Between ADHD With Anxiety and ADHD-Only Groups—Children’s Characteristics.

	ADHD-only (n = 87)	ADHD + ANX (n = 33)	p value
Children’s characteristics
Age	8.2 ± 1.7	8.8 ± 1.6	.083
Gender
M	65 (74.7%)	25 (75.8%)	1.000
F	22 (25.3%)	8 (24.2%)
Repeat grade	5 (5.7%)	2 (6.1%)	1.000
Long-term medical problems	8 (9.2%)	2 (6.1%)	.725
Abuse history^a	2 (2.3%)	2 (6.1%)	.303
Parents’ marital status
Cohabitate/married	78 (89.7%)	27 (81.8%)	.352
Separated/divorced	9 (10.3%)	6 (18.2%)
Immigrant parents^b	41 (47.1%)	13 (39.4%)	.539
Family income
Lower than median^c	38 (43.7%)	13 (39.4%)	.836
Equal/more than median^b	49 (56.3%)	20 (60.6%)

Positive abuse history was defined by the formal registration in local family and child protective services units.

Parents are immigrants from Mainland China.

Median of monthly domestic household income (Census and Statistics Department, 2011b).

Table 3.

Comparison Between ADHD With Anxiety and ADHD-Only Groups—Mother’s Characteristics.

	ADHD-only (n = 87)	ADHD + ANX (n = 33)	p value
Mother’s characteristics
Mother’s age	37.8 ± 5.3	40.1 ± 4.7	.036
Mother with current/lifetime psychiatric disorder	15 (17.2%)	5 (15.2%)	1.000
Mother’s occupation status
Unemployed	43 (49.4%)	18 (54.5%)	.747
Unstable work	6 (6.9%)	3 (9.1%)
Stable work	38 (43.7%)	12 (36.4%)
Mother’s education level
No formal education	4 (4.6%)	1 (3.0%)	.786
Primary school	6 (6.9%)	4 (12.1%)
Secondary school	64 (73.6%)	24 (72.7%)
Tertiary/above	13 (14.9%)	4 (12.1%)
Alcoholism history of mother	1 (1.1%)	0	1.000
Substance abuse history of mother	1 (1.1%)	1 (3.0%)	.476
Mother’s HADS
Anxiety score	6.4 ± 4.0	7.9 ± 4.9	.107
Anxiety above cutoff	32 (37%)	17 (52%)	.152
Depression score	5.9 ± 3.8	6.5 ± 3.9	.448
Depression above cutoff	38 (44%)	16 (49%)	.684
Total score	12.2 ± 7.5	14.4 ± 8.2	.174
Total above cutoff	35 (40%)	16 (49%)	.418

Note. HADS = Hospital Anxiety Depression Scale.

Clinical profiles

Children with anxiety disorders were more likely to exhibit comorbid ODD/CD. A total of 54.5% of children in the ADHD + ANX group exhibited comorbid ODD/CD, whereas only 27.6% of children in the ADHD-only group exhibited comorbid ODD/CD (p = .009, Table 4). Children in the ADHD + ANX group exhibited more inattention symptoms than did children in the ADHD-only group, as indicated by both the inattention symptom and criteria counts (Table 4).

Table 4.

Comparison Between ADHD With Anxiety and ADHD-Only Groups—Clinical Profiles.

	ADHD-only (n = 87)	ADHD + ANX (n = 33)	p value
Inattention type	31 (35.6%)	13 (39.4%)	.832
Hyperactive type	8 (9.2%)	1 (3.0%)	.441
Combined type	48 (55.2%)	19 (57.6%)	.840
Inattention symptom count	8.4 ± 1.6	9.1 ± 1.1	.009
Hyperactivity symptom count	6.0 ± 3.1	6.0 ± 3.2	.864
ADHD total symptom count	14.4 ± 3.4	15.0 ± 3.3	.391
Inattention criteria count	7.4 ± 1.5	8.2 ± 1.1	.003
Hyperactivity criteria count	5.6 ± 2.9	5.5 ± 2.9	.796
ADHD total criteria count	13.0 ± 3.1	13.7 ± 3.0	.327
ODD/CD diagnosis	24 (27.6%)	18 (54.5%)	.009
ODD/CD criteria count last year	0.32 ± 0.25	0.42 ± 0.33	.104
ODD/CD symptoms count	0.65 ± 0.46	0.84 ± 0.59	.102

Note. ODD/CD = oppositional defiant disorder or conduct disorder. Bold indicates items with p value < 0.05.

Parental internalizing psychopathologies

Contrary to our hypothesis, the parents of the children with ADHD + ANX reported overall more anxiety and depressive symptoms, but with no statistical differences between the two (Tables 3 and 5).

Table 5.

Comparison Between ADHD With Anxiety and ADHD-Only Groups—Father’s Characteristics.

	ADHD-only (n = 87)	ADHD + ANX (n = 33)	p value
Father’s characteristics
Father’s age	43.6 ± 6.5	44.7 ± 6.6	.421
Father with current/lifetime psychiatric disorder	6 (6.9%)	4 (12.1%)	.460
Father’s occupation status
Unemployed	7 (8.0%)	2 (6.1%)	.711
Unstable work	12 (13.8%)	3 (9.1%)
Stable work	68 (78.2%)	28 (84.8%)
Father’s education level
Primary school	8 (9.2%)	2 (6.1%)	.580
Secondary school	71 (81.6%)	26 (78.8%)
Tertiary/above	8 (9.2%)	5 (15.2%)
Alcoholism history of father	3 (3.4%)	1 (3.0%)	1.000
Substance abuse history of father	1 (1.1%)	2 (6.1%)	.183
Father’s HADS
Anxiety score	5.9 ± 4.1	6.8 ± 4.1	.358
Anxiety above cutoff	36 (41%)	20 (61%)	.068
Depression score	5.2 ± 3.7	6.6 ± 3.8	.138
Depression above cutoff	34 (39%)	20 (61%)	.034
Total score	11.1 ± 7.4	13.4 ± 7.5	.210
Total above cutoff	37 (43%)	20 (61%)	.102

Note. HADS = Hospital Anxiety Depression Scale.

Multivariable Analysis

Binary logistic regression was conducted to evaluate the relationship between anxiety disorders (dependent variable) and the other variables, which had revealed significant differences (p < .1) in univariate analysis. Both age and sex were controlled. Candidate variables included maternal age, maternal HADS anxiety sub-score, paternal HADS depression sub-score, inattention symptoms/criteria count, ODD/CD symptoms/criteria count, and categorical comorbid diagnoses of ODD/CD. The results revealed that inattention criteria counts and comorbid ODD/CD diagnoses were significantly associated with anxiety disorders in children with ADHD. The adjusted odds ratio of the inattention criteria count was 1.51, whereas this ratio was 3.04 for comorbid ODD/CD diagnoses (Table 6).

Table 6.

Backward Logistic Regression Analysis Significant Findings Only.

	B	SE	p value	Exp(B) (odds ratio)	95% CI for Exp(B)
	B	SE	p value	Exp(B) (odds ratio)	Lower	Upper
Mother age	0.10	0.05	.05	1.11	1.00	1.23
Inattention criteria	0.41	0.21	.05	1.51	1.10	2.27
ODD/CD	1.11	0.49	.02	3.04	1.19	7.79

Note. ODD/CD = oppositional defiant disorder or conduct disorder.

Discussion

Comorbidity Rate

The present study is the first to report the prevalence of anxiety disorders diagnosed using structured interviews among children with ADHD aged 6 to 12 years in Hong Kong. The concurrent comorbidity rate was 27.5%, which is consistent with the findings of previous Asian and Western studies despite the differences in the definitions of these disorders (Biederman et al., 1991; Byun et al., 2006; Gau et al., 2010; Jensen et al., 1997). This rate was significantly higher than the prevalence of anxiety disorders in this community, which was 6.9% in our local epidemiological study on children without ADHD using the same diagnostic criteria as those in our study (P. W. Leung et al., 2008).

The new Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; APA, 2013) defines ADHD based on the same 18 symptoms used in the DSM-IV and continues to divide these into two symptom domains. The revisions were focused to identify symptoms of ADHD across an individual’s life span, particularly during adolescence and adulthood. The changes in anxiety disorders are relatively minor. Obsessive compulsive disorder (OCD) and posttraumatic stress disorder (PTSD) are no longer classified as anxiety disorders but are separated into new categories. In the present study, no child was diagnosed with PTSD, but two children were diagnosed with both ADHD and OCD. These two children were also diagnosed with other anxiety disorders. The changes in the criteria for agoraphobia, specific phobia, and social anxiety disorder included elimination of the requirement that individuals aged more than 18 years must recognize whether their fear and anxiety were excessive or unreasonable. The specific symptoms indicating separation anxiety disorder remained unaltered, although the diagnostic criteria no longer specified that the age of onset must be before 18 years. Furthermore, the 6-month duration requirement now applies to all ages instead of being limited to individuals aged less than 18 years, as implemented in the DSM-IV. These changes were intended for guiding clinicians to accurately diagnose ADHD and anxiety disorders in adults. Overall, these revisions have limited impacts on the participants in our study who were aged only 6 to 12 years. The prevalence rates of anxiety disorders among children with ADHD in our study were similar to previous finds upon applying the new DSM-5 criteria.

Nature of Anxiety in Hong Kong Chinese Children With ADHD

More frequently, the anxiety symptoms reported by community studies were subclinical with little functional impairment (P. W. Leung et al., 2008; Romano, Tremblay, Vitaro, Zoccolillo, & Pagani, 2001). The aforementioned local epidemiological study reported that 30.2% children and adolescents presented with elevated anxiety symptoms, but only 6.9% of them were diagnosed with fully developed anxiety disorders (P. W. Leung et al., 2008). By contrast, in the present study, 49.2% of the participants exhibited elevated anxiety symptoms, and 27.5% of them were confirmed with clinical anxiety disorders (Table 1). Moreover, the children often exhibited multiple anxiety disorders, particularly those with specific phobia. These findings are consistent with those of a previous epidemiological study, which reported that children with specific phobia also exhibited other comorbid mood and anxiety disorders (Essau, Conradt, & Petermann, 2000). The onset of specific phobia occurs primarily at childhood and subsequently becomes a chronic condition (Boyd et al., 1990). However, caregivers and clinicians often ignore or underestimate the importance of specific phobia. Thus, only a small proportion of such children receive appropriate treatment. Therefore, clinicians should carefully consider and screen for anxiety disorders among children with ADHD, particularly those with specific phobia, who may be suffering from multiple anxiety disorders, which often indicates severe clinical phenomenology and psychosocial factors (Franco, Saavedra, & Silverman, 2007), and hence, identification of the affected children and provision of appropriate treatment is critical.

Comorbidity With ODD/CD

In the present study, over 50% of the children with ADHD and anxiety disorders exhibited comorbid ODD/CD, with an adjusted odds ratio of 3.0. Thus, children with both ADHD and ODD/CD were 3 times more likely to develop anxiety disorders. These findings are consistent with those of the MTA study, wherein two thirds of the ADHD participants with anxiety disorders exhibited comorbid ODD/CD, with an odds ratio of approximately 2 (p < .001) for anxiety (March et al., 2000).

Both our findings and those of the MTA study were consistent with the foundational observations reported by Denhoff, Laufer, and Solomons (1957): “The presence of the hyperkinetic syndrome does not offer any immunity against the development of neuroses, while the resulting symptom picture from frustrating circumstances is generally not of a neurotic type.” The MTA study explained that a parental report of anxiety on the DISC may actually reflect the negative affectivity (NA) associated with disruptive behavior instead of the fearfulness and phobic symptoms considered in the conventional conceptualization of anxiety (March et al., 2000). NA is a general dimension of subjective distress and unpleasant engagement that encompasses various aversive mood states, including anger, contempt, disgust, guilt, fear, and nervousness. In addition, it reflects the pervasive individual differences in negative emotionality and self-concept, which has been associated with most childhood psychopathologies, including both internalizing and externalizing disorders (Clark & Watson, 1991). People who express high NA typically view themselves and various aspects of the world around them in negative terms, such that negative consequences are inevitable. A community study further revealed substantial overlap between parental report of anxiety and the construct of NA among children with ADHD (Baldwin & Dadds, 2008). All these observations indicated that ADHD and anxiety disorders may be influenced by common factors such as ODD or NA (Lilienfeld, 2003). Additional studies are warranted to specifically investigate this inter-relationship and understand the exact nature of anxiety in children with ADHD.

Association With Inattention

Our findings suggest an association between anxiety disorders and inattention symptoms, with an adjusted odds ratio of 1.5. In the MTA study, the anxious participants displayed more inattentive symptoms, whereas those with CDs exhibited more hyperactive and impulsive symptoms (Newcorn et al., 2001). Similarly, an epidemiological study by Baldwin also revealed a positive association between ADHD and anxiety symptoms, which were associated with inattention symptoms (Baldwin & Dadds, 2008). A systematic review conducted to explain these observations based on neuropsychological findings and the specific nature of anxiety in children with ADHD reported that the presence of anxiety in ADHD may partially inhibit impulsivity (Schatz & Rostain, 2006). Moreover, the anxiety may worsen working memory and other cognitive deficits. In addition, the anxiety experienced by children with ADHD may exhibit a greater association with the inability to perform activities of daily living because of social and cognitive insufficiencies than a typical phobic or fearful behavior. The fear of poor cognitive performance observed in children with ADHD may further hinder the cognitive performance, which was the original source of anxiety. Therefore, this may explain why the presence of anxiety disorders in children with ADHD is often associated with the severity of inattention symptoms.

Absence of Association With Maternal Anxiety and Depression

Surprisingly, both parental anxiety and depression levels were not associated with anxiety disorders in children with ADHD, in contrast to the findings of a systematic review of general population, which showed a large overlap between children’s and parental anxiety levels (Cartwright-Hatton, McNicol, & Doubleday, 2006). We predicted that reporter bias, genetic factors, and environmental mechanisms (e.g., maternal anxious attachment perceptions, maladaptive parenting practices, parental modeling of anxiety, and avoidance) may account for the association between parental psychopathology and anxiety in children (Burstein, Ginsburg, & Tein, 2010). The failure to illustrate this finding may be attributed to the limitations of the measurement tool used. HADS is a screening tool that focuses on the anxiety and depression levels in the preceding week before assessment and does not reflect the pervasive anxiety and depression states.

However, it may still be possible that the single effect of maternal psychopathology does not significantly influence the anxiety levels in this particular group of children. Biederman et al. (1995) studied the familial environment of children with ADHD and focused on the compelling work by Rutter and coworkers, stating that it was the aggregation of multiple adversity factors, including maternal mental disorder, rather than the presence of a single factor, which led to the impairment in ADHD and its psychiatric comorbidities. Kepley and Ostrander (2007) suggested that the degree of maternal control affected a child’s anxious behaviors the most and that in an anxious ADHD family, independence and autonomy were often discouraged. Therefore, the presence or absence of parental anxiety or depression may not have affected the anxiety levels of the children in our study.

Limitations

The findings of this study should be considered in the context of several methodological limitations. Because the children in our study sample were enrolled from a tertiary care center, the results may not be generalizable to other community samples or epidemiologically based reports. In addition, the most severely ill children were possibly referred to the tertiary care center for service, which could inflate the apparent comorbidity prevalence of anxiety among children with ADHD.

Parents were the only informants in this study, which may not reflect the complete picture of anxiety in children with ADHD. Direct incorporation of information from the child by using a diagnostic measurement tool focusing on pediatric anxiety disorders might have produced different results. Thus, future studies must focus on the local translation and validation of such measurement tools. Although teachers are not ideal observers of internalizing problems in children and are more prone to exhibit a halo effect in reporting symptoms of ADHD, studies have reported that teachers rate oppositional and conduct behaviors more accurately (Abikoff, Courtney, Pelham, & Koplewicz, 1993). Even though the primary focus of the study was anxiety disorder, the inter-relationship between externalizing and internalizing psychopathologies in children with ADHD necessitates an accurate simultaneous measurement of the externalizing problems. The inclusion of teachers’ reports of ODD/CD symptoms in future studies would clarify their role in the model by decreasing the effects of shared reporter bias.

Moreover, our sample size was inadequate for analyzing individual anxiety disorders, and only significant variables in univariate analyses were included in the binary logistic regression studies.

Finally, contrary to our expectations, no significant association was observed between parental internalizing psychopathologies and the anxiety levels in children. In addition, as explained earlier, the self-report questionnaire only evaluated the parent’s condition during the preceding week before assessment; therefore, future studies must consider using an appropriate diagnostic assessment tool, such as the structured clinical interview for DSM-IV (SCID), which covers a longer period or even lifetime of symptoms, to measure parental psychopathologies.

Clinical Implications and Conclusion

Despite the aforementioned limitations, the present study focusing on Chinese children in Hong Kong diagnosed with ADHD based on structured interviews enables a relevant comparison with the findings of similar Western studies and provides evidence to guide future investigations.

Considering the externalizing nature of ADHD symptoms, anxiety is easily overlooked by teachers, caregivers, and clinicians. However, it affects over one fourth of the Hong Kong Chinese children with ADHD, whereas the children often exhibited multiple anxiety disorders. In addition, the risk of anxiety disorders increases further in the presence of comorbid ODD/CD. Therefore, children with ADHD should be screened and carefully assessed for anxiety in routine clinical practice, particularly those with comorbid ODD/CD.

Although no significant association was observed between the children’s anxiety disorders and the parental internalizing psychopathologies, approximately 50% of the parents of children with ADHD exhibited clinical anxiety and depression. Certain recent large scale studies have demonstrated an association between maternal depression and poor parenting behaviors, and that both maternal and paternal psychopathologies were positively associated with antisocial behaviors in children (Gerdes et al., 2007; Vera, Granero, & Ezpeleta, 2012). In addition to the high prevalence rate of parental anxiety and depression, we also identified high prevalence rate of comorbid ODD/CD among children with ADHD (n = 42, 35% of all participants). The mental health of parents of children with ADHD should be properly addressed. Based on the results of this study, parent sessions directly targeting at parental anxiety and depression as part of behavioral therapy for families of children with ADHD, similar to the treatment programs for parents when treating childhood conduct problems, may prove useful. Taken together, the behavioral therapies should be administrated to treat the parental internalizing psychopathologies and conduct problems in children, modify the parenting behaviors in families of children with ADHD, and provide improved outcomes.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Author Biographies

Caroline K. S. Shea, MBCHB, FHKAM (Psych), Department of Psychiatry, Alice Ho Mui Ling Nethersole Hospital.

Marshall M. C. Lee, MBBS, FHKAM (Psych), Department of Psychiatry, Alice Ho Mui Ling Nethersole Hospital.

Kelly Y. C. Lai, MBBS, MRCPsych, FHKAM (Psych), Associate Professor, Department of Psychiatry, The Chinese University of Hong Kong.

Ernest S. L. Luk, MBBS, MRCPsych, MD, FRANZCP, FHKAM (Psych).

Patrick W. L. Leung, PhD, Department of Psychology, The Chinese University of Hong Kong.

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