Are subtypes of attention deficit actually unrelated disorders?

An assessment of research in Attention Deficit Hyperactivity Disorder subtypes recently examined the possibility that the hyperactive/combined and inattentive subtypes of ADHD might be two distinct disorders rather than subtypes of a single one.

Robert Milich and colleagues at the University of Kentucky report that there are important
differences in the features, demographics, cognitive and neuropsychological functioning, family history, treatment response, and prognosis of these subtypes. Since the ADHD criteria were changed to include the inattentive subtype in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, a 15 percent increase in the number of ADHD cases has been reported.

These new cases were more than twice as likely to be girls and most were of the inattentive subtype. Milich et al. assert that a review of the research suggests that the inattentive group is a valid disorder but probably not a member of the ADHD family. The subtypes have no defining features in common, which challenges the assumption that they share some common core deficit. The inattentive symptoms include sluggishness, hypoactivity, and daydreaming behaviors.

The symptoms of the hyperactive/combined subtypes are disinhibition, distractibility, and hyperactivity. Children diagnosed as exhibiting a hyperactive attention disorder are much more likely to be boys, to have had an earlier onset of symptoms, to be actively rejected by peers and to have other acting-out behavior problems.

In contrast, the children diagnosed as inattentive are more often girls, more likely to have a math disability and to have internalizing problems such as anxiety or depression, as well as to be shy and withdrawn with their peers.

In addition, there is some evidence that the inattentive and hyperactive/combined groups respond differently to stimulant medication. Milich et al. call for more research, but believe that redefining these groups as separate disorders will eliminate some debate and help to clarify the underlying mechanisms involved in these disorders.

They state that removing the inattentive group from the ADHD category will clarify the research issues and create a more focused research agenda for the study of inattention. This will also encourage physicians, psychologists and educators to provide more tailored interventions for inattentive children.


“ADHD Combined Type and ADHD Predominantly Inattentive Type Are Distinct and Unrelated Disorders,” Clinical Psychology: Science and Practice, Volume 8, Number 4, Winter 2001, pp. 463-493.

Published in ERN February 2002 Volume 15 Number 2


Leave a Reply

  • (will not be published)