META-ANALYSIS: MRI VOLUMETRIC DATA OF CHILDREN WITH ADHD SUBTYPES by Amanda Lynn Hysell A Thesis Presented to the Faculty of the School of Graduate Psychology of California Lutheran University In Partial Fulfillment of the Requirements for the Master of Science Degree with an Emphasis in Clinical Psychology The signatures below certify that the Master Thesis of Amanda Hysell has been approved by the School of Psychological Sciences of California Lutheran University in partial fulfillment of the requirements for the degree Master of Psychology Approved: Accepted: Sunyoung Park, PhD Jamie Bedics, PhD, ABPP Thesis Committee Chair Director of Graduate Program in Clinical Psychology Jamie Bedics, PhD, ABPP Richard Holligrocki, PhD Committee Member Dean, Graduate School of Psychology Date Date ABSTRACT Attention-deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder consisting of inattentive and/or hyperactive behaviors that is typically prevalent in childhood. There are three recognized subtypes of this disorder— hyperactive, inattentive, and combined. The current study’s purpose is to examine how the subtypes differentiate based on brain structure volume size. There have been studies on ADHD subtypes and brain structure volumes in children, but there are a number of limitations in available research that make it difficult to generalize findings.
A meta-analysis was done using 8 studies that included volumetric data of ADHD subtypes (inattentive and combined) in children that was acquired through magnetic resonance imaging (MRI) techniques. Analyses were done looking at combined and inattentive type in comparison to controls and between the two groups. Further subgroup analyses were done on gender and brain regions in the two subtypes. Results show that there is a significant brain volume reduction in combined type in comparison to controls and inattentive type.
There is also a significant volume reduction observed in males. The other analyses done yielded insignificant findings, although the volume reduction in inattentive type was only slightly above the cutoff of alpha (0. These findings help in better understanding the relations between brain volume and ADHD subtypes, but further research is still needed in this area. Keywords: ADHD, combined, inattentive, MRI, brain volume iii ACKNOWLEDGEMENTS I would like to thank Dr.
Jaime Bedics for the support and feedback you provided on my thesis. I would also like to extend my gratitude for seeing the potential in me and giving me the chance to be a part of this program. Through this opportunity, I was able to grow academically and professionally. With the immense and continuous support of the faculty, I have developed a new level of confidence in both research and statistics.
I would also like to thank Dr. Sunyoung Park for being an incredible professor and guiding me through each step of my thesis. I was able to learn several statistical models with ease thanks to your approaches to teaching. Your support throughout this program has tremendously helped strengthen my skillset.
The overall experience working with you and Dr. Bedics has greatly prepared me to move forward in my pursuit of a doctorate program. iv TABLE OF CONTENTS Page Abstract. iv List of Tables.
vi List of Figures. vii SECTIONS Introduction. 55 v LIST OF TABLES Page Table 1. Result of Pooled Effect Size with Robust.
27 Variance of Estimation Table 2. Results from Moderator Analysis with Type. 29 of ADHD (ADHD-I vs. Results from Moderator Analysis for Gender.
Results from Subgroup Analyses- Hemisphere. Results from Subgroup Analyses- Right Caudate. 35 Nucleus (RCN) and Left Caudate Nucleus (LCN) vi LIST OF FIGURES Page Figure 1. MRI Scan of Healthy Child.
Example of How Volumetric Data is. 12 Collected Using MRI Scans Figure 3. Studies for Meta-Analysis (PRISMA). 23 Chart of Literature Search for ADHD Subtypes and Volumetric Data of MRI Scans of the Brain Figure 4.
Forest Plot of Effect Sizes Included in Study. Funnel Plot of Effect Sizes Included in Study. 36 vii BRAIN VOLUMES AND ADHD SUBTYPES IN CHILDREN 1 Meta-Analysis: MRI Volumetric Data of Children with ADHD Subtypes Attention-deficit hyperactivity disorder (ADHD) is neurodevelopmental disorder with a typical onset in childhood or early adolescence. The disorder consists of patterns of inattentiveness and/or hyperactivity.
With three categorical subtypes (inattentive, hyperactive, and combined), there are a number of ways this disorder can manifest in an individual (American Psychological Association [APA], 2013). Although the exact prevalence is unknown at this time, it is estimated that 8.4% of children in the United States have a current diagnosis of ADHD (Children and Adults with Attention-Deficit/Hyperactivity Disorder [CHADD]; n. There are not accurate estimates available for the prevalence of the individual subtypes. Children with ADHD experience a number of deficits and impairments in cognitive, behavioral, and emotional functioning (Brown, 2002; Kaiser et al.
Some of these core deficits are also apparent across the subtypes (Mayes et al., 2009; Kaiser et al. Although there is extensive research available on ADHD, there is still a lot that is unknown. Research has unveiled that ADHD has neuroanatomical underpinnings. This is validated by studies examining brain regions in relation to ADHD.
Research has provided evidence that there are structural brain differences in individuals with ADHD, typically in the form of decrease in structural volume sizes (Vilgis et al., 2015; Carrey et al. Less is known about structural differences in the subtypes in children since this area is less BRAIN VOLUMES AND ADHD SUBTYPES IN CHILDREN 2 frequently examined in its entirety. Current research on the subtypes has found mixed results, with some reporting volume decrease, some reporting volume increase, while others report no differences in volume size at all (Vilgis et al., 2015; Al-Amin et al., 2017; Bledsoe et al., 2009; Pineda et al. It is important to further understand the areas that are affected in relation to the subtypes and the clinical implications this could have.
The disorder has a high prevalence and the use of the subtype classification is the current diagnostic practice. Structural data could expand on the understanding of ADHD subtypes, confirm the current classification system, act as a diagnostic tool, and aid in treatment planning. BRAIN VOLUMES AND ADHD SUBTYPES IN CHILDREN 3 Literature Review Attention-Deficit Hyperactivity Disorder (ADHD) ADHD is a neurodevelopmental disorder recognized by the Diagnostic and Statistical Manual-5 (DSM-5). The DSM-5 classifies ADHD as a persistent pattern of inattention and/or hyperactivity that interferes with functioning or development.
The DSM-5 has defined inattention as having such traits as not giving close attention to details, difficulty sustaining attention to tasks, and not listening when spoken to. Hyperactivity and impulsivity have been defined as, but not limited to, exhibiting frequent fidgeting, inability to remain seated, and running and climbing when inappropriate (APA, 2013). In order to meet diagnostic criteria, six or more symptoms of inattention and/or hyperactivity and impulsivity need to be present for at least 6 months to a degree that is not appropriate for the developmental level the individual is at. The symptoms must impact functioning in at least two settings and be present to a large degree prior to age of 12 years (APA, 2013).
Starting with the DSM-IV, ADHD was broken down into subtypes. Following this system, the DSM-5 offers three specifications under the ADHD diagnosis – combined presentation (C), predominantly inattentive presentation (I), and predominantly hyperactive/impulsive presentation (H; APA, 2013). ADHD-I diagnosis requires that the majority of symptomology falls under inattentiveness, whereas ADHD-H is predominantly hyperactive and impulsive behaviors. ADHD-C is a fair distribution BRAIN VOLUMES AND ADHD SUBTYPES IN CHILDREN 4 of impairments in attention and hyperactivity and is thought to be the most common subtype of the three (APA, 2013).
Since there are several variations in how this disorder can be classified, there are a number of developmental, emotional, and cognitive domains that are at risk for being impaired in children with ADHD. Executive functioning is one of the more frequent deficits observed in this disorder. Impairments of executive functioning can be broken down into 6 clusters (Brown, 2002). The clusters include activation, focus, effort, emotion, memory, and action.
Activation is the difficulty in planning tasks, estimating time, and prioritizing. Focus entails difficulty in focusing, sustaining focus, or shifting focus from one task to another. Effort is the difficulty in alertness, effort, and processing speed. Emotion is the difficulty in managing frustration and regulating emotions.
Memory is the difficulty using working memory and recalling information. Action is the challenge in monitoring and regulating one’s actions (Brown, 2002). ADHD has a major impact on the performance in school settings. Children with this disorder have been found to have slightly lower intelligent quotients (IQ) than comparison groups (Biederman et al.
ADHD affects academic achievement over the course of development, with untreated groups performing at lower standards than those receiving treatment and typically developing children (Arnold et al. BRAIN VOLUMES AND ADHD SUBTYPES IN CHILDREN 5 Across all settings, a large proportion of Children with ADHD have deficits in fine and gross motor skills (Kaiser et al. They also display slower speeds in motor activation (Borger & Meere, 2000). Children with ADHD are also more likely to experience sleep disturbances, such as problems falling and remaining asleep (Stein, 1999).
There are differences in how ADHD symptomology manifests dependent on gender. School-aged children with ADHD differ in classroom behaviors based on gender. Girls are more likely to be verbally aggressive, whereas boys demonstrate higher rates of rule-breaking and externalizing behavior (Abikoff et al. Physical aggression is higher in boys with ADHD than girls (Carlson et al.
Boys with higher rates of combined and hyperactive-impulsive subtypes have a higher degree of impairment in social functioning, academic performance, and self- esteem (Graetz et al. Research has found a number of disparities in ADHD dependent on race and ethnicity. Minority children have been found to be less likely to be diagnosed with ADHD, with Black children being 70% less likely than White children to receive this diagnosis (Morgan et al., 2013; Morgan et al. Being raised in an English-speaking household has been found to be a risk factor that increases the chances of receiving an ADHD diagnosis, which is supported by the findings that Latinx/Hispanic children are less likely than White children to receive this diagnosis if they come from a non-English speaking household (Morgan et al., BRAIN VOLUMES AND ADHD SUBTYPES IN CHILDREN 6 2013; Morgan et al.
A factor found to decrease the chances of receiving an ADHD diagnosis is not having health insurance (Morgan et al. Racial and ethnic minority groups are less likely than Whites to be uninsured, and although this gap has drastically closed since the introduction of the Affordable Care Act, these differences are still present (Chaudry et al. Due to this, it is unclear if the data on the diagnosis of ADHD in racial and ethnic minority groups is an accurate reflection of the prevalence of this disorder or the result of inaccessibility. There has also been an observed difference in racial and ethnic minorities and the treatment they receive, with minority groups being less likely than Whites to take prescription medication for the disorder (Morgan et al.
There are observed differences in behavior when looking at the individual subtypes. Children with ADHD-I are less likely to experience sleep disturbances than those with ADHD-C (Mayes et al. Children with ADHD-I are more likely to demonstrate impairments in fine motor abilities, slower reaction times, and motor control in comparison to those with ADHD-C (Kaiser et al. Children with ADHD-C have higher rates of impairment in social functioning and pro-social behavior, and the tendency to be disliked by peers (Willcutt et al.
Children and adolescence with ADHD-C are also more likely to be sustain injuries that require medical attention (1998, as cited in Willcutt et al. ADHD is frequently diagnosed in combination with other developmental disorders at an estimated rate of 67% (Elia et al. Internalizing and BRAIN VOLUMES AND ADHD SUBTYPES IN CHILDREN 7 externalizing disorders are commonly observed with this disorder.