Attention Research Update

November 2007

"Helping parents, professionals and educators stay informed about new research on ADHD"

David Rabiner, Ph.D.  Senior Research Scientist, Duke University


Important New Findings on an Objective Test for ADHD


Like all psychiatric disorders, ADHD is diagnosed based on the presence of specific behavioral symptoms that are judged to cause significant impairment in an individual's functioning, and not on the results of any specific test.  In fact, recently published ADHD evaluation guidelines from the American Academy of Pediatrics (AAP) explicitly state that no particular diagnostic test should routinely be used when evaluating a child for ADHD.  Instead, the AAP outlines a comprehensive set of guidelines to insure that DSM-IV diagnostic criteria for ADHD are met.  You can find a description of those criteria at http://www.helpforadd.com/criteria.htm

While most ADHD experts would agree that no single test could or should be used in isolation to diagnose ADHD, there are several important reasons why the availability of an accurate objective test would be useful.

First, most children are evaluated for ADHD by primary care pediatricians.  Despite efforts by the AAP to promote careful and comprehensive ADHD evaluation procedures by it's members, the reality of primary care practice is that many physicians are not able to devote the 2-4 hours of time required for a comprehensive evaluation.  As a result, many children are diagnosed with ADHD based on evaluation procedures that not optimal.

Second, although AAP guidelines indicate that specific diagnostic tests should not be routinely used, many parents are concerned about the lack of objective procedures in their child's evaluation.  In fact, in a recently published study involving 850 families who did not pursue treatment as recommended by their child's physician's, it was reported that 90% of these families cited the absence of objective evaluation procedures as an important reason for their decision.  The absence of objective procedures led these families to question their child's diagnosis, which made them reluctant to pursue treatment recommendations.

These factors - the difficulty obtaining comprehensive evaluations and the desire of many parents for an objective component to their child's evaluation - suggest that an accurate and objective diagnostic test for ADHD could be of value in many clinical situations. 

For such a test to be useful, two important conditions would have to be met.

First, the test would need to be highly sensitive to the presence of ADHD.  This means that individuals who truly have ADHD as determined by a comprehensive evaluation should score positive for ADHD on the test.  If the test were 100% sensitive, than every individual who truly has ADHD based on current diagnostic criteria would score positive on the diagnostic test.  As the sensitivity of a test drops, the number of "false negative" results that it produces, i.e., individuals who truly have the disorder but who score normal on the test, increases.

Second, individuals who don't have ADHD should never score positive on the test, i.e., a positive result should be specific to ADHD and nothing else.  When a diagnostic test has high specificity, individuals without the condition being tested for rarely score positive on the test.  If a diagnostic test is not highly specific, individuals who don't have a particular condition can be incorrectly diagnosed as having it based on their test results.  This is referred to as a "false positive".

Although many psychological tests have been shown to yield different results, on average, for individuals with and without ADHD, the problem is that they are not sensitive or specific enough to be particularly useful when making diagnostic decision about individuals.

For example, a widely used objective test in ADHD evaluations are Continuous Performance Tests (CPTs).  These tests provide an accurate computerized measure of a child's ability to sustain attention and refrain from impulsive responding.

The limitation of CPTs as a diagnostic test for ADHD, however, is that a substantial percentage of children with ADHD perform adequately on them, i.e., they yield an unacceptably high level of false negatives.  In addition, because attention problems can result from a variety of difficulties besides ADHD, e.g., depression, anxiety, trauma, poor sleep, CPT results do not do a good job of differentiating ADHD from other psychiatric conditions or difficulties in a child's life.  Thus, although CPT data can be useful for some purposes when thoughtfully integrated with other information obtained in a comprehensive evaluation, heavily relying on CPTs to rule in or rule out ADHD would be highly problematic based on currently available data.


- Is there anything better? -

In several past issues of Attention Research Update I have reviewed studies on the use of Quantitative EEG, i.e., QEEG, as a diagnostic procedure for ADHD.  The use of QEEG is based on the premise that individuals with ADHD have a distinctive pattern of brain electrical activity that some investigators refer to as "cortical slowing".  What this distinctive pattern involves is that EEG activity in people with ADHD is characterized by an elevation of low frequency theta waves and a reduction of higher frequency beta waves.  Theta wave activity is associated with a more unfocused and inattentive state while beta activity is associated with more focused attention.  Thus, an elevated theta/beta ratio is indicative of a less alert and attentive state.

In a QEEG testing, EEG data is collected from a child or adult in a roughly 30 minute non-invasive procedure.  The EEG data is digitized and computer scored and the theta/beta ratio for the individual is computed.  That ratio is compared to what is typically found in age-matched individuals so that the deviation from what is typical can be determined.  If the individual tested has a significantly elevated ratio - the cut-off typically used is 1.5 standard deviations above average, which corresponds to the highest 7% of the population - he or she is considered to show the EEG marker for ADHD.

In past studies, roughly 90% of individuals diagnosed with ADHD based on a comprehensive evaluation consistent with best practice guidelines, were found to score positive for this EEG marker.  In contrast, about 95% of normal controls were found to score negative.  Thus, although not a perfectly reliable indicator, the sensitivity and specificity of the QEEG indicator for correctly detecting the presence or absence of ADHD were extremely strong.  You can review these studies at http://www.helpforadd.com/2001/april.htm  and http://www.helpforadd.com/yr2000/april.htm 

The important limitation of this past work, however, is that the QEEG procedure was only used to differentiate between individuals already known to have ADHD and comparison subjects without any disorder.  Differentiating between ADHD and no disorder, however, is not the situation that clinicians typically face.  Instead, a child is referred because of attention and/or behavior problems and the clinician must determine whether these problems truly reflect ADHD, are better explained by another disorder, or do not rise to the level where any particular diagnosis is appropriate.  Thus, for QEEG to be a truly useful tool to assist in diagnosing ADHD, it must be shown to be helpful for this more challenging task of "differential diagnosis".


- An Encouraging New Study on QEEG for differential diagnosis -

A study published in a recent issue of Psychiatry Research provides an important test of whether QEEG can be useful in differentiating ADHD from other psychiatric problems [Quintana, Snyder, Purnell, Apontye, & Site (2007). Comparison of a standard psychiatric evaluation to rating scales and EEG in the differential diagnosis of ADHD. Psychiatry Research, 152, 211-222.]

Participants were 26 6 to 21 year-olds (23 males and 3 females) recruited from a child psychiatric clinic at the LSU Health Sciences Center.  Subjects were included if they presented to the clinic because a parent and/or school official suspected the child or adolescent might have ADHD. Participants were not on any psychiatric medications at the time of the study.


- Psychiatric Evaluation -

Participants received a standard psychiatric evaluation conducted by a board certified child psychiatrist and psychiatric research fellows.  Each parent and child/adolescent were interviewed using a semi-structured interview called the K-SADS that inquired about ADHD symptoms as well as symptoms for a variety of other disorders.  This is a widely used psychiatric interview that has been shown to be reliable and valid.  Information about impairment from symptoms - a necessary criteria for diagnosing ADHD - was obtained using standardized rating scale measures of impairment.  The psychiatric evaluation required 2-3 hours to complete.


- EEG Evaluation -

EEG data collection and analysis were performed 3-7 days after the psychiatric evaluation by technicians who were completely blind to the psychiatric evaluation results.  EEG was recorded during two conditions for 3 minutes each: eyes closed and eyes open with fixed attention on a point on the wall at eye level.

As discussed above, the theta/beta ratio was computed for each participant and compared to data from a large normative sample.  Participants were said to have the EEG marker for ADHD if their theta/beta ratio was 1.5 standard deviations higher than the average ratio for their age group.  This corresponds to roughly the top 7% of the population.


- Rating Scale Evaluation -

Parents completed the ADHD Rating Scale on their child or adolescent.  This instrument asks parents to rate their child on each of the 18 DSM-IV symptoms of ADHD.  Participants whose score on this measure was 1.5 standard deviations above the age-matched mean for inattentive and/or hyperactive-impulsive symptoms were considered to have ADHD according to the rating scale.


- Assigning ADHD Diagnoses -

The lead psychiatrist compiled the information from the psychiatric evaluation and performed the diagnosis of each subject, designating ADHD or non-ADHD.  The psychiatrist also assigned other diagnoses that were present in addition to ADHD, or, in some cases, instead of ADHD.  For ADHD to be diagnosed, it had to be the primary diagnosis and deemed to be the primary focus of treatment.

Diagnosis by the child psychiatrist based on the psychiatric evaluation was  considered the "gold standard' against which diagnoses based on EEG and rating scale data were compared. Thus, the diagnosis of each participant was made without any knowledge of the EEG or rating scale results.  To determine whether the EEG test and the rating scale results were accurate in correctly identifying the presence vs. absence of ADHD, the researchers simply examined the level of agreement between the psychiatrist's diagnosis with the diagnosis made based on the EEG and rating scale results alone.


- Results -

Of the 26 children and adolescents who were initially suspected of having ADHD, 16 met DSM-IV criteria for the disorder based on the comprehensive psychiatric evaluation.  Five were diagnosed with the combined type of ADHD (both inattentive and hyperactive-impulsive symptoms) and 10 with the inattentive type, and one with the hyperactive-impulsive type.  Four received at least one other diagnosis in addition to ADHD. The remaining 10 subjects did not qualify for an ADHD diagnosis; 9 received 1 or more other diagnoses and 1 did not qualify for any diagnosis.

There were no significant age differences between participants according to whether or not they received an ADHD diagnosis.  The two groups were also equivalent on the standardized ratings of impairment.  Thus, the presence or absence of ADHD was not related to the degree to which they were judged to be struggling in important life areas.


- Accuracy of Parent Rating Scale -

Of the 16 subjects judged to have ADHD by the psychiatric evaluation, 13 screened positive for ADHD on the rating scale measure.  Of the 10 non-ADHD subjects, 7 were falsely identified as having ADHD.  This rate of false positives is unacceptably high and indicates that relying on parent rating scale results alone to diagnose ADHD - which should never be done - is likely to result in substantial over diagnosis of ADHD.


- Accuracy of EEG Measure -

Fifteen of the 16 participants diagnosed with ADHD by the child psychiatrist had a theta/beta ratio above the ADHD cut-off. This included all participants with the inattentive or combined subtype; the only participant with ADHD missed by the EEG marker was the lone child with the hyperactive-impulsive subtype. In contrast, none of the 10 participants without ADHD showed the EEG marker of ADHD, even though all were referred because of concerns related to ADHD. Thus, classification based on EEG results matched the results of the psychiatric evaluation in 25 of 26 cases.


- Summary and Implications -

Results of this study are certainly impressive.  The EEG results correctly identified the presence or absence of ADHD - which was determined independently by a comprehensive psychiatric evaluation - in 25 of 26 cases.   What makes this result particularly important is that this was not differentiating children with ADHD from normal controls.  Instead, this study demonstrated that QEEG can reliably differentiate between ADHD and other disorders in children and adolescents for whom ADHD was initially suspected.  The reliance on a parent rating scale for diagnostic purposes was far less accurate.

Despite the impressive nature of these findings, there are two important limitations to this study that the authors note.  First, the sample is relatively small and all participants were drawn from a single clinical site.  It would thus be very important to replicate these results in a larger sample in which participants were drawn from multiple clinical settings.

Second, and of particular importance, the researchers did not incorporate direct input from teachers in their evaluation process.  This is a notable omission in that although a psychiatric interview with parents is the cornerstone of child and adolescent ADHD evaluations, collecting data on the child's behavior and functioning directly from school personal is recommended by the American Academy of Pediatrics and the American Academy of Child and Adolescent Psychiatry. 

Because parents and teachers often perceive a child's behavior differently, it is certainly possible that incorporating such information would have changed the child psychiatrist's diagnosis of ADHD in one or more cases.  Any such change, except for the one case where EEG and evaluation results disagreed, would have lowered the overall classification accuracy of the EEG test.

Despite these limitations, this is an important study that adds to an already substantial research base on the utility of QEEG as a diagnostic aid for ADHD.  This does not mean, of course, that QEEG should ever be used in isolation to establish or rule out the diagnosis of ADHD for any individual. 
Even if the test were 100% accurate in matching results from a "gold standard" evaluation, the goals of a comprehensive evaluation for ADHD go beyond merely deciding whether the disorder is present. Instead, the diagnostician must identify the presence of other disorders that may complicate treatment, identify specific targets to address in treatment, as well as other factors that may be contributing to a child's difficulties. These are all important parts of the evaluation process that no single test for ADHD, no matter how accurate, can possibly do.

In situations where comprehensive evaluations are not possible, however, QEEG may at least do a good job of replicating the results of such an evaluation with respect to the presence vs. absence of ADHD.  If nothing else, this could prevent children from being diagnosed with ADHD inappropriately and placed on medications that will not address their actual problem.  This objective indicator may also be helpful in situations where parents have a strong desire for an objective confirmation of a physician's diagnosis arrived at by standard assessment methods.

Thus, while not a substitute for a careful and comprehensive evaluation, the exciting results from this study suggest that the use of QEEG may play a very helpful role in the evaluation of ADHD in many clinical situations.


Information presented in Attention Research Update is for informational purposes only, and is not a substitute for professional medical advice.  Although newsletter sponsors offer products and services that I believe will be of interest to subscribers, sponsorship of Attention Research Update does not constitute a specific endorsement or guarantee of any company's product or services.