ADHD Combined Type and ADHD Predominantly Inattentive Type Are Distinct and Unrelated Disorders

Abstract

We comprehensively reviewed research assessing differences in attention-deficit hyperactivity disorder (ADHD) subtypes to examine the possibility that ADHD/ combined type (ADHD/C) and ADHD/predominantly inattentive type (ADHD/I) are distinct and unrelated disorders. Differences among subtypes were examined along dimensions identified as being important in documenting the distinctiveness of two disorders. These include essential and associated features, demographics, measures of cognitive and neuropsychological functioning, family history, treatment response, and prognosis. Important differences among subtypes were found in several areas of study, supporting the conclusion that ADHD/C and ADHD/I may best be characterized as distinct disorders. We identify major limitations of the available research and present future directions for research.The history of the classification of attention-deficit hyperactivity disorder (ADHD) is rife with controversies. Early concerns were raised over whether ADHD and conduct disorders (CD) were distinct disorders or whether the classification of these disorders could be handled more parsimoniously by combining them into a broader, externalizing category. Although this controversy has been resolved in favor of distinct externalizing categories (Hinshaw, 1987), other diagnostic debates have come to the

Neuropsychological functioning of girls with attention-deficit/hyperactivity disorder followed prospectively into adolescence: Evidence for continuing deficits?

“…In fact, in both the childhood-diagnosed and adolescent-diagnosed analyses, these "type" differences were never significant except for one instance for the adolescent-diagnosed girls, even though power calculations reveal that, given our follow-up sample sizes, we have statistical power of nearly .6 to detect effects of medium size (see Faul & Erfelder, 1992). Despite contentions that the inattentive type of ADHD is a separate, qualitatively distinct variant of this disorder, particularly with respect to cognitive performance (Milich et al, 2001), we found no such evidence, at least with respect to the variables in our battery. Whether other cognitive measures would yield such effects must await additional research.…”

“…Given claims that this variant of ADHD represents a qualitatively distinct condition (Milich, Balentine, & Lynam, 2001), such followup is a priority, particularly with respect to objective outcomes, which are likely to be less biased than reports from adult informants.…”

Long-term deficits of preterm birth: Evidence for arousal and attentional disturbances

“…In general, the incidence of ADHD did not seem related to P50 potential amplitude. Interestingly, our study sample had a higher representation of females with ADHD (24% in females and 14% in males), consistent with others who have found a similar male to female ratio for ADHD in Ex-Preterm children compared to male predominance of ADHD in the general population (Milich et al 2001).…”

Academic Achievement Over 8 Years Among Children Who Met Modified Criteria for Attention-deficit/Hyperactivity Disorder at 4–6 Years of Age

“…It is possible that the predominantly inattentive subtype exhibits problems with inattention that are more severe than those experienced by children with the combined subtype in their impact on academic learning. On the other hand, the present findings raise the possibility that younger children who meet criteria for the inattentive type have qualitatively different problems (Milich, Balentine, & Lynam, 2001). For example, it is possible that the inattentive group has serious deficits in academic skill learning that lead to their symptoms of inattention.…”