EEG-defined subtypes of children with attention-deficit/hyperactivity disorder
Introduction
Attention-deficit/hyperactivity disorder (ADHD) is one of the most common disorders treated by child and adolescent psychiatrists in America, with this group of children comprising as much as 50% of child psychiatry clinic populations (Cantwell, 1996). Studies based on DSM-IV criteria (American Psychiatric Association, 1994) have found the prevalence of children with ADHD to range from 3 to 6% (Pelham et al., 1992, Lindgren et al., 1990), with the DSM-IV estimating prevalence at approximately 3–5% of school-age children. A major concern with this population is the level of subjectivity which is involved in diagnosis. At the present time, no reliable objective measures of ADHD exist. Diagnosis is almost always based on the observations and perceptions of the child's parents, which assumes that a parent has an accurate knowledge of what is normal age-appropriate behaviour.
EEG research over the last 30 years has found fairly consistent group differences between children with or without ADHD. These include increased theta activity (Satterfield et al., 1972, Janzen et al., 1995, Clarke et al., 1998, Clarke et al., 2001b, Clarke et al., 2001c) which occurs primarily in the frontal regions (Mann et al., 1992, Chabot and Serfontein, 1996, Lazzaro et al., 1998), increased posterior delta (Matousek et al., 1984, Clarke et al., 1998, Clarke et al., 2001b, Clarke et al., 2001c) and decreased alpha and beta activity (Dykman et al., 1982, Callaway et al., 1983), also most apparent in the posterior regions (Mann et al., 1992, Clarke et al., 1998, Clarke et al., 2001b, Clarke et al., 2001c, Lazzaro et al., 1998). Increases in the theta/alpha (Matousek et al., 1984, Ucles and Lorente, 1996, Clarke et al., 1998, Clarke et al., 2001b, Clarke et al., 2001c) and theta/beta (Lubar, 1991, Janzen et al., 1995, Clarke et al., 1998, Clarke et al., 2001b, Clarke et al., 2001c) ratios have also been found in children with ADHD compared to normal children. Although detailed discussion is beyond the scope of this paper, these EEG differences may contribute substantially to the auditory and visual event-related potential differences which are reported from such children (e.g. Johnstone et al., 2001, Johnstone and Barry, 1996, Steger et al., 2000).
Following these studies, a number of researchers have investigated the utility of discriminant function analysis of such EEG measures in the diagnosis of ADHD (Lubar et al., 1985, Mann et al., 1992, Chabot and Serfontein, 1996, Chabot et al., 1999, Hughes and John, 1999, Hoffman et al., 1999). However, this procedure has been criticized on the basis of poor sensitivity and specificity (Levy and Ward, 1995, Rey, 1997, Nuwer, 1997).
One problem with the majority of these studies is that they have conceptualized their clinical groups as being homogenous, which may not be an accurate assumption. It is possible that the mean group differences reported may not accurately reflect the nature of the EEG deviance found in individual children with ADHD. Several studies have reported distinct EEG groups within their clinical samples. Clarke et al., 1998, Clarke et al., 2001c, Clarke et al., 2001d found between 15 and 20% of children with a diagnosis of ADHD combined type (ADHDcom) had significantly elevated levels of beta activity in their EEG. Chabot and Serfontein (1996) and Chabot et al. (1999) also reported the existence of distinct subsets of children with ADHD, separately characterized by excess theta, alpha and beta activity. These studies suggest that children with a diagnosis of ADHD may constitute a heterogeneous group with different underlying electrophysiological abnormalities.
This study aimed to investigate EEG similarities and differences within a group of boys with ADHDcom to determine whether their EEG profiles clustered into meaningful groups. Such clusters could form the basis for an EEG-defined subtyping of ADHD children and assist our understanding of brain dysfunction in the disorder.
Section snippets
Subjects
Subjects in this study consisted of 184 children with a diagnosis of ADHDcom and 40 age-matched control subjects. All children were between the ages of 8 and 12 years and were right-handed and right-footed. Subjects had a full-scale Weschler Intelligence Scales for Children (WISC)-III IQ score of 85 or higher. The children with ADHD were drawn from new patients presenting at a Sydney-based paediatric practice for an assessment for ADHD. The clinical subjects had not been diagnosed as having
Results
Principal component analysis identified two similar factors within each frequency band (see Table 1). The first factor primarily loaded on the frontal electrode sites and the second factor loaded on the posterior sites. However, there was a relatively high but inconsistent loading of the central sites and T3 and T4 on both factors. Rather than exclude these sites, it was decided to include them as a third regional grouping. The factor analysis thus suggested the grouping of scalp sites into 3
Discussion
EEG studies of children with ADHD have typically found increased theta activity (Satterfield et al., 1972, Mann et al., 1992, Janzen et al., 1995, Chabot and Serfontein, 1996, Lazzaro et al., 1998, Clarke et al., 1998, Clarke et al., 2001b, Clarke et al., 2001c), increased posterior delta (Matousek et al., 1984, Clarke et al., 1998, Clarke et al., 2001b, Clarke et al., 2001c), decreased alpha and beta activity (Dykman et al., 1982, Callaway et al., 1983, Mann et al., 1992, Clarke et al., 1998,
Acknowledgements
We wish to thank Peter Caputi for assistance with the statistical analyses used in this study.
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