The relationship between internalizing symptoms and attention deficit/hyperactivity disorder symptoms: a study ofChinese primary students in Hong Kong

Abstract

Objective: Current studies examining the co-morbidity patterns of ADHD with internalizing disorders have reported inconsistent findings. Some studies have found that the inattentive subtype (ADHD-I) is more likely to be comorbid with internalizing disorders, while other studies found similar levels of comorbid internalizing disorders between the ADHD subtypes. Moreover, anxiety and depression were found to be comorbid in inattentive children high in sluggish cognitive tempo (SCT), characterized by features of sluggishness, drowsiness, and daydreaming. SCT has been postulated to be useful in discriminating a distinct inattentive subtype of ADHD-I with a different pattern of impairments. More recently, low levels of behavioral inhibition (BI)—manifested in the form of disinhibited behaviors—have also been implicated in the development of ADHD in children. The current study examines the relationships between ADHD and internalizing symptoms. The roles of SCT and BI in ADHD and internalizing symptoms are also investigated.

Methods: The sample was comprised of 1,965 Hong Kong primary students between 8 and 14 years old and their parents/caregivers from 10 local schools. The children completed two self-report scales: the Revised Children Anxiety and Depression Scale (RCADS) and the Behavioral Inhibition System Scale (BISS). Their parents/caregivers completed three scales: the Attention Deficit Hyperactivity Disorder Rating Scale–IV (ADHDRS-IV), the Oppositional Defiant Disorder Scale (ODDS), and the Sluggish Cognitive Tempo Scale (SCTS). Using a psychometric approach, the relationships between the symptom clusters of ADHD (inattention and hyperactivity-impulsivity), anxiety, depression, SCT, and BI were systematically examined with correlation, regression, and factor analyses. A categorical approach was also used to classify children meeting the DSM symptom criteria to compare levels of internalizing symptoms among the three subtypes of ADHD: ADHD-I, ADHD-HI (hyperactive-impulsive), and ADHD-C (combined hyperactive and inattentive). An SCT cutoff score of 20 (the mean SCT rating among ADHD-I children) was used to further divide the ADHD-I into high- and low-SCT subgroups for planned between-group comparisons.

Results: In the dimensional analyses, the inattention dimension of ADHD correlated slightly higher than the hyperactivity-impulsivity dimension with anxiety and depression as predicted. But the hyperactivity-impulsivity dimension was also significantly correlated with anxiety and depression, suggesting that hyperactive children were as likely as inattentive children to feel anxious and depressed. Regression analyses found that inattention was not predictive of anxiety and depression, while hyperactivity-impulsivity was marginally predictive of anxiety, but not depression. BI and SCT emerged as significant predictors of internalizing symptoms after controlling for age, gender, and ODD symptoms. There was evidence that SCT mediated the relationship between anxiety/depression and inattention symptoms.

Using the categorical approach, between-group differences were found between the ADHD subtypes and the no-ADHD category. ADHD-I children were more anxious and depressed than children without ADHD. Differences in depressive symptoms were found between the ADHD subtypes. Children with ADHD-I had higher levels of depressive symptoms when compared to children with ADHD-HI and ADHD-C. Contrary to predictions, however, the high-SCT ADHD-I group and the low-SCT ADHD-I group did not differ in symptom levels for any anxiety disorders, major depressive disorder, or externalizing symptoms of ODD. Subtype differences in comorbid anxiety were found to be related to gender differences. The symptom levels of panic disorder were higher in females with ADHD-I, and the symptom levels of separation-anxiety disorder were higher for females with ADHD-C. Inattentive girls might present with higher levels of anxiety symptoms than boys.

Conclusions: Consistent with previous studies, children with ADHD were more comorbid with anxiety and depression than children without ADHD. In addition, children with ADHD-I were more comorbid with depressive symptoms than children with ADHD-HI and ADHD-C. The higher ratings of depression in ADHD-I children appeared to be related to higher ratings of SCT found in this subtype. There was no difference in anxiety symptoms among the ADHD subtypes, but girls with clinical levels of inattention tend to experience a wider spectrum of anxiety disorders than boys.

Contrary to previous research, the findings did not support the idea that SCT is useful in discriminating a distinct inattentive subtype, since this study found no comorbidity differences between the high-SCT ADHD-I and low-SCT ADHD-I groups. Despite the fact that the ADHD-I group had higher BI, there was no evidence that they had higher anxiety symptoms. Reasons for the lack of a direct relationship between BI and internalizing symptoms in ADHD are discussed. The complex roles of SCT and BI in ADHD symptoms and internalizing symptoms call for the need of further local investigation in both clinical and community samples.