Research Developments and Their Implications for Clinical Care of the ADHD Child

Attention-deficit/hyperactivity disorder (ADHD) has received an extraordinary amount of attention in the popular media over the past eight months. Stories concerning the disorder, and especially its treatment with stimulant medication, have appeared in many major newspapers, news magazines and television news, entertainment and talk show programs. Such widespread news coverage, as well as the success of parent support associations in disseminating information on ADHD and recent best-selling books on the topic, ensured that clinicians would be called upon increasingly to evaluate, diagnose and manage individuals with this disorder.

Those services might seem relatively simple and straightforward to the uninitiated, especially given that ADHD has been recognized for quite some time. Explicit criteria for its diagnosis have been available for nearly 16 years in the Diagnostic and Statistical Manual for Mental Disorders (DSM) and practice guidelines for the evaluation and treatment of ADHD have been disseminated by the American Academy of Child and Adolescent Psychiatry. This, along with several thousand scientific papers and books on the subject, might suggest that the nature of ADHD, its diagnosis and management have been about as well-specified as any childhood disorder to date.

Such complacency, however, would be wrong. There is much that is new or newly emerging about the nature of this disorder, as well as the most effective approaches to its management. Several hundred new scientific papers on ADHD appear in our scientific journals each year, and there is a good deal of excitement and promise in several "cutting edge" areas of research such as behavioral genetics, neuroimaging and neuropsychology. All of this is challenging and changing our understanding of this disorder, its diagnosis and its management. My purpose here is to highlight some of these advances in understanding ADHD and the changes they may herald for the clinical care of children (and even adults) with ADHD. Space permits highlighting only a few here, however.

For several decades, clinical wisdom has held that ADHD comprises three primary symptoms: inattention, hyperactivity and impulsivity. While not constituting a scientific theory, this descriptive view nevertheless proved practical in the yeoman's work of explaining the disorder to others (patients, family members, etc.) and reasonably represented the findings of the scientific literature of the time. As in any vibrant area of science, however, additional findings began to overtake this view, calling into question its adequacy for representing or accounting for the newly emerging findings in the scientific literature. These findings also stressed the need for some type of overarching theoretical or conceptual model of ADHD apart from just the clinical description set forth in the DSM. Significant among these trends in research were the following, all of which challenged the current descriptive approach to ADHD (Barkley, in press).

New Conceptual Model

First, the inattention seen in ADHD may not be the first set of problems to arise in development-hyperactive-impulsive symptoms seem to emerge first, typically in the preschool years. Second, the hyperactive and impulsive symptoms are not two primary or independent constructs but form a single deficit (now called hyperactivity-impulsivity in DSM-IV), which I have come to call disinhibition (Barkley 1990).

Third, the inattentiveness seen in the hyperactive-impulsive (HI) and combined types of ADHD is not in the "input," or information-processing aspects of neuropsychological functioning where attention is often thought to reside, but more likely in the "output," or response-programming and execution aspects.

Related to that point is a fourth: the inattention seen in children with ADHD, predominantly inattentive (PI) type- also known as ADD without hyperactivity- may actually be a qualitatively different problem than the type of inattention seen in ADHD, HI or combined types- a problem with focused/selective attention versus one of poor goal-directed persistence and interference control (inhibiting distraction) (Barkley, in press; Barkley and colleagues; Goodyear and Hynd; Lahey and Carlson).

All of this leads to interesting implications for the nature of ADHD, chief among which is that we have possibly two separate and qualitatively distinct disorders on our hands. The PI type may be the true attention disorder while the other two types are simply different developmental stages of the same disorder, one that involves behavioral disinhibition that ultimately results in poor goal-directed persistence and defective resistance to distraction (Barkley, in press).

If research continues to support such a distinction, it is quite likely that the diagnostic criteria for each should be separate, with a new list of inattentive symptoms created to more accurately reflect this qualitative distinction of the PI type from the other types. Certainly a different name for this new disorder would be needed (say, attention-deficit disorder) that distinguished it from ADHD (which might better be called behavioral inhibition disorder, or BID). And this new ADD would probably be removed from the metacategory of the disruptive behavior disorders as it seems to share little if any comorbidity with oppositional defiant or conduct disorders, as do the other types of ADHD (BID).

The treatments for these two disorders may prove to be different as well. This is already hinted at in several studies of stimulant medication with these subtypes. There, the PI type has shown a lower rate (prevalence) of positive response to medication (65 percent versus 92 percent), a smaller magnitude or degree of positive response when one is seen, with the most optimal dose being toward the lower end of the therapeutic range as compared to moderate or higher doses (Barkley and colleagues 1991). Should further research replicate these initial findings, it will indicate that stimulants may not be the medications of choice for the PI type of ADHD; their response is hauntingly familiar to that seen in normal children placed on stimulants (Rapoport and colleagues). And while various behavioral or contingency management interventions may still be of assistance for the PI type, they are likely to be so for reasons that are different from why they are needed and helpful in the management of the HI or combined types. The cognitive behavioral therapies may even prove more useful for the PI type although they were of questionable efficacy for the HI or combined types (Abikoff; Diaz and Berk).