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An Objective Procedure for Assessing ADHD?
An ongoing concern among both parents and professionals in regards to evaluating children for ADHD is the lack of an "objective" procedure for making the diagnosis. Currently, a careful evaluation involves combining information from multiple sources (i.e. parents, teachers, and child) using both interview and behavior rating scale data. Depending on the particular circumstances, the use of formalized psychological tests may also be incorporated. In the end, however, the diagnosis is based on the clinician's best judgment using all available sources of data
Although there is overwhelming support for the fact that well-trained clinicians using empirically based procedures are able to make the diagnosis of ADHD in a reliable and valid manner, many object to the fact that the diagnosis still comes down to the clinician's "judgment". (Of course, it is important to be aware that this is no different from the diagnosis of any other type of psychiatric disorder.) In response to this concern, there have been several efforts to develop "objective" procedures for diagnosing ADHD, the most widely used of these being the Continuous Performance Test (i.e. CPT - you'll find a brief description of this procedure below).
Recent data on the differences found in different aspects of brain structure and function in individuals with ADHD have also contributed to the hope that an "objective" diagnostic procedure used sophisticated technologies could be developed. The problem with such technologies for diagnosis, however, is that they have not been sensitive or specific enough to be used for diagnosing individuals. In other words, even though groups of individuals with ADHD appear different using such procedures compared to groups of individuals without ADHD, there has generally been a fair amount of overlap between the groups. Thus, some individuals with ADHD do not look any different from "normal" subjects on these tests and some "normal" subjects produce results that are similar to those found in many ADHD individuals. Using these technologies as the basis for diagnosis would thus lead to many diagnostic errors that would "identify" false positives (i.e. diagnosing someone with ADHD who did not have it) and false negatives (i.e. failing to diagnose someone with ADHD who had the condition).
A study published in a recent issue of Neuropsychology, however, provides initial evidence of the potential utility of at least one objective procedure for diagnosing ADHD Monastra, V.J., et al. (1999). Assessing ADHD via quantitative electroencephalography, Neuropsychology, 13, 424-433). The hypothesis underlying this study is that cortical slowing in the prefrontal region of the brain can serve as a basis for differentiating individuals with ADHD from nonclinical control groups. (Recall the article from the March issue of ADHD RESEARCH UPDATE in which enhancing physiological arousal - and presumably cortical activity - was associated with improved performance on several tasks by children with ADHD. This is also consistent with the hypothesis that cortical underactivity in particular brain areas is the underlying biological basis for ADHD.)
Participants in this study were 482 individuals between the ages of 6 and 30. Both males and females were well- represented in the sample. Participants were classified into 3 groups (i.e. ADHD-Inattentive Type, ADHD-Combined Type, and controls) on the basis of the results of a standardized clinical interview, behavioral rating scales, and a Continuous Performance Test (i.e. CPT). The CPT is a procedure in which individuals sit in front of a computer screen and are required to press - or not press - certain keys depending on which stimuli appear on the screen. It is designed to evaluate both sustained attention and impulsivity, and is one of the most frequently used "objective" procedures to aid clinicians in evaluating individuals for ADHD. (For a discussion of the distinction between the inattentive and combined subtype of ADHD click here.)
Cortical activity in the prefrontal region for these participants was then assessed using a quantitative electroencephalographic procedure (QEEG) - a technique that assesses electrical activity in particular brain areas. The question of interest is the degree to which individuals who had been previously diagnosed with ADHD on the basis of more traditional diagnostic procedures would also be correctly identified as having ADHD or not, based on these QEEG data alone.
Results
The results were impressive. Overall, the authors report that this "diagnostic test" yielded sensitivity and specificity results of 86% and 98% respectively. This means is that 86% of the individuals diagnosed with ADHD using the conventional diagnostic procedures were also classified as having ADHD using the QEEG procedure alone. Similarly, 98% of those who did not have ADHD according to the interview, CPT, and rating scale data were not classified as having ADHD using the QEEG data. Thus, there was substantial agreement between the diagnostic determinations made using these very different approaches. Consistent with what has been found previously, individuals with ADHD were found to produce results on the QEEG that indicated cortical slowing (i.e. less activity in the brain area being evaluated). According to the authors, these results held up across the two subtypes of ADHD and for both genders as well.
Because some researchers - notably Russell Barkley - have suggested that the inattentive subtype of ADHD is likely to represent a very different condition that the hyperactive/impulsive or combined subtypes, it is especially interesting that similar results were obtained for the inattentive and combined subtypes in this study. This suggests that individuals with these different subtypes of ADHD may have a common neurological feature (i.e. slowed cortical activity in the prefrontal areas of the brain) in common, although additional research on this issue is necessary prior to making any such conclusion.
Implications
The results of this study would seem to provide promising initial evidence that this procedure may have important utility as an "objective" test for diagnosing ADHD. It is important to remember, however, that one's opinion about this depends on what you think the "gold standard" for diagnosis should be. If you believe that careful interviews of parents, teachers, and children - along with the collection of standardized behavior rating scales - provides the most complete set of data on which to make a diagnostic decision, then the procedure investigated here still failed to identify about 14% of individuals of having ADHD who "really did".
To put this another way, what should one do when information from parents and teachers - and perhaps even direct observational data - all support an ADHD diagnosis for a child, but the QEEG does not? A prudent approach in this instance would be to first be sure to rule out possible alternative explanations for the symptoms that are being so prominently displayed. For example, one would want to be sure that the child's symptoms were not better explained by some type of mood or anxiety disorder, reaction to a recent stressor, elevated lead levels, etc.. If all plausible alternatives are ruled out, however, than what? Does one want to conclude that it can not be ADHD because the "objective" QEEG data is inconsistent with this?
I don't think there is a clear-cut answer to a question like this, but this is an important issue to consider as efforts to further develop objective diagnostic procedures for ADHD proceed onward. It would have been quite interesting if the authors provided more detailed information about what seemed to be going on among these participants in their study (i.e. those who were diagnosed with ADHD using the traditional means but not the QEEG). Nonetheless, this is a very interesting study that provides initial information on what may become a useful component of the diagnostic process. Replications of these results in an independent sample is of course required - as the authors note - before the utility of this approach becomes clearer.
It is also important to note that there was no clinical control group in this study - i.e. participants without ADHD but with some other psychiatric diagnosis. Thus, it is possible that the procedure they used may be effective for distinguishing between people with and without some type of psychiatric diagnosis, rather than being specific to ADHD per se. Future studies should include a clinical control group in addition to "normal" controls so that this important issue can be disentangled. For example, if the authors find that their QEEG procedure is just as effective in differentiating individuals with ADHD from individuals with another psychiatric diagnosis, as it was here in distinguishing people with ADHD from non-psychiatric control subjects, the results would be even more impressive.
Note: This article originally appeared in Attention Research Update, an online newsletter written by Dr. David Rabiner, a Duke University psychologist and former member of CHADD's Professional Advisory Board. You can learn more about Attention Research Update and sign up for a free subscription at www.helpforadd.com.