An Objective Test
to Help Diagnose ADHD: Quantitative EEG
Like all psychiatric disorders, ADHD is diagnosed based
on the presence of particular behavioral symptoms that are judged to cause
significant impairment in an individual's functioning, and not on the results
of a specific test. In fact, recently published ADHD evaluation guidelines
from the American Academy of Pediatrics (AAP) explicitly state that no particular
diagnostic test should be routinely used when evaluating a child for ADHD.
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, many children do not receive a careful and comprehensive assessment
for ADHD but are instead diagnosed with based on evaluation procedures that
are far from 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, many families do not
pursue treatment for ADHD because the the absence of objective evaluation
procedures leads them to question the diagnosis. You can read a review of
an interesting study on this issue at http://www.helpforadd.com/2006/january.htm
For these reasons an accurate and objective diagnostic test for ADHD could
be of value in many clinical situations. Two important conditions would have
to be met for such a test to be useful.
First, it would have to be highly sensitive to the presence of ADHD, i.e.,
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,
every individual who has ADHD based on current diagnostic criteria would
score positive on the test. As the sensitivity of a test drops, the
number of "false negatives" - normal test results in individuals who truly
have the disorder increase and its utility goes down.
Second, individuals who don't have ADHD should never score positive on the
test, i.e., a positive result should occur only for individuals with ADHD
and no one else. When a diagnostic test has high specificity, individuals
without the condition rarely score positive on the test. When specificity
is low, many individuals without the condition will score positive and may
be incorrectly diagnosed as a result. This is referred to as a "false positive".
Although many psychological tests yield different results, on average, for
individuals with and without ADHD, they are not sensitive or specific enough
to be particularly useful when making individual diagnostic decisions. For
example, a widely used objective test in ADHD evaluations are Continuous
Performance Tests (CPTs). These tests provide a computerized measure
of a child's ability to sustain attention and refrain from impulsive responding.
Although average performance on CPTs for children with ADHD is below that
of peers, and CPT data can be helpful when thoughtfully integrated with other
diagnostic information, these tests yields too many false positives and false
negatives to be useful as an "objective" diagnostic test for ADHD.
Is there anything better?
Several past issues of Attention Research Update have reviewed Quantitative
EEG, i.e., QEEG, as a diagnostic aide for ADHD. The use of QEEG is
based on findings that individuals with ADHD have a distinctive pattern of
brain electrical activity that is often referred to as "cortical slowing";
this is characterized by an elevation of low frequency theta waves and a
reduction of higher frequency beta waves in the prefrontal cortex.
Theta wave activity is associated with an unfocused and inattentive state
while beta activity is associated with more focused attention. Thus,
an elevated theta/beta ratio reflects a less alert and more unfocused state.
In a QEEG testing, EEG data is collected from a child or adult in a non-invasive
procedure that requires about 30 minutes. The EEG data is digitized and computer
scored so that an individual's theta/beta ratio can be computed; this ratio
is then compared to what is typical for individuals of similar age.
When this ratio is sufficiently elevated ratio - the cut-off typically used
is 1.5 standard deviations above average which corresponds to the highest
7% of the population - the individual is considered to have the EEG marker
In past studies, roughly 90% of individuals diagnosed with ADHD based on
a comprehensive evaluation tested positive for this EEG marker. In
contrast, about 95% of normal controls tested negative. Thus, while
not a perfectly reliable indicator, the sensitivity and specificity of QEEG
in identifying ADHD was extremely strong. You can review these studies
The important limitation of this work was that QEEG was tested using individuals
known to have ADHD and normal controls 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
reflect ADHD, are better explained by another disorder, or do not rise to
the level where any diagnosis is appropriate. Thus, for QEEG to be
useful in ADHD evaluations, it must also accurately distinguish between ADHD
and other disorders.
One recently published preliminary study indicated promising findings in
this regard. Twenty-six children and adolescents referred to an outpatient
psychiatry clinic for attention and behavior problems received a thorough
ADHD assessment conducted by a team of child psychiatrists. They also
received a QEEG evaluation. Sixteen of the 26 were determined to meet
DSM-IV criteria for ADHD by the psychiatric team while 10 were diagnosed
with other conditions. Of the 16 diagnosed with ADHD, 15 showed the
QEEG marker for ADHD; in contrast, none of the 10 diagnosed with other conditions
showed the QEEG marker. Thus, the QEEG test performed extremely well.
A comprehensive review of this study can be found at http://www.helpforadd.com/2007/november.htm
While these results were encouraging, the sample was small and from a single
clinical site. This raises important questions about the generalizability
of the findings that need to be addressed in a study that incorporates a
larger sample drawn from multiple clinical sites. Recently, a study
meeting these criteria was published; I believe it is one of the most interesting
and important studies I have seen in several years [Snyder et al. (2008).
Blinded, multi-center validation of EEG and rating scales in identifying
ADHD within a clinical sample. Psychiatry Research, 159, 346-358.]
- Participants were 159 6-18-year-olds (101 males and
58 females) taken by parents to 1 of 4 pediatric and psychiatric clinics
because of concerns related to attention and behavior problems. One
hundred and fifteen were children (6-11 years old) and the remainder were
adolescents. There was a good representation of African Americans in
the sample (37%).
Psychiatric and Medical Exam
- At each site, children received a standardized
psychiatric evaluation that included a semi-structured interview (the KSADS-PL)
and measures of functional impairment and disorder severity. Both parents
and children/adolescents were interviewed, the optimal procedure for covering
both externalizing and internalizing disorders. Other clinical procedures
included taking a medical history, a developmental history, and providing
a physical exam.
Using results of these interviews and associated measures, the clinical team
performed a complete differential diagnosis for the presence of ADHD, comorbid
conditions, and other childhood/adolescent disorders. Diagnostic decisions
about ADHD followed a standard protocol to determine whether strict DSM-IV
diagnostic criteria were met. The team's determination about the presence
or absence of ADHD was considered the "gold standard" against which diagnostic
decisions based on behavior rating scales and QEEG were compared.
- Parents and teacher completed 2 behavior rating scales
that are widely used in the assessment of ADHD - the Conners Rating Scale
and the ADHD-IV Rating Scale. Children were considered to be positive
for ADHD if their scores on these scales exceeded the recommended cut-off
for identifying ADHD. This enabled the researchers to determine how
well diagnostic decisions derived fro rating scales agreed with results from
the comprehensive psychiatric exam.
- EEG data was collected on each child using standard collection
procedures by trained EEG technicians. The theta/beta ratio computed
for each child and compared to values for age matched controls from a large
normative data base. Participants whose theta/beta ratio was at 1.5
standard deviations above the average score, i.e., roughly the top 7%, were
considered to show the EEG marker for ADHD.
It is important to note that diagnostic decisions from the psychiatric evaluation
were made without the team having any access to rating scale or QEEG data.
Thus, decisions made about the presence or absence of ADHD from the psychiatric
evaluation was not influenced in any way by knowledge of these other results.
The logic of this study is simple and straight forward. The authors
treated results of the psychiatric exam as the "gold standard" for determining
which of the 159 participants met diagnostic criteria for ADHD. Then,
they examined how well results based on the behavior rating scales and the
EEG exam matched this standard.
Ninety-seven of the 159 children and adolescents (61%) were diagnosed with
ADHD by the psychiatric evaluation. Sixty-four of these children were
diagnosed with at least 1 other disorder, 35 had at least 2 additional disorders,
and 11 had at least 3 additional disorders. The most common comorbidities
were one of the disruptive behavior disorders (Oppositional Defiant Disorder
or Conduct Disorder) which occurred in 66 of the 97, followed by an anxiety
disorder (46 of 97), learning disorder (33 of 97), and mood disorder (23
Of the 62 participants not meeting criteria for ADHD, all but 8 were diagnosed
with one of these other disorders while 8 had no diagnosis.
Overall, therefore, this was a diverse clinical sample that included the
full range of psychiatric difficulties that clinicians are called on to address.
How accurate were behavior rating scales at identifying ADHD?
The behavior rating scales did not perform well. The results were as follows:
ADHD-IV Parent - 28% false negatives, 67% false positives, 56% overall accuracy.
ADHD-IV Teacher - 62% false negatives, 39% false positive, 47% overall accuracy.
ADHD-IV P&T combined - 45% false negatives, 57% false positives, 50%
Conners Parent - 22% false negatives, 86% false positives, 55% overall accuracy.
Conners Teacher - 33% false negatives, 59% false positives, 58% overall accuracy.
Conners P&T combined - 28% false negatives, 81% false positives, 53%
As can be seen, the rate of false negatives (children diagnosed with ADHD
based on the psychiatric evaluation that scored below the recommended ADHD
cut-off on the rating scale) ranged from 28% for the parent version of the
Conners Rating Scales to 62% for the teacher version of the ADHD-IV rating
False positive rates (children without ADHD based on the psychiatric evaluation
who scored positive for ADHD on the rating scale) ranged from 39% to 86%.
The extremely high false positive rate for the parent version of the Conners
indicates that parents tended to rate their child high on ADHD symptoms even
when ADHD was not judged to be present.
Overall classification accuracy - how often rating scale results agreed with
psychiatric evaluation results - was below 60% for every scale. Thus,
the level of agreement was not much better than chance.
The accuracy of QEEG as a diagnostic test was much higher - the false negative
rate was only 13% and the false positive rate was only 6%; this resulted
in an overall accuracy rate of 89%. These figures indicate the following:
- 87% of children diagnosed with ADHD by the psychiatric evaluation showed
the EEG marker for the disorder;
- 94% of children without ADHD screened negative for the EEG marker;
- If ADHD diagnosis was based strictly on the presence or absence of the
EEG marker, it would match decisions based on the psychiatric evaluation
almost 90% of the time.
Overall, these results are far superior to the classification accuracy using
Extending the findings to different subgroups and comorbidities
Because participants represented a diverse clinical sample, the researchers
could test whether QEEG accuracy was similar for children vs. adolescents,
whites vs. blacks, and males vs. females. Across these different demographic
groups, overall accuracy rates ranged from 87% to 95%. Thus, QEEG worked
well within all demographic groups.
The authors also examined whether diagnostic accuracy of the QEEG was consistent
depending on whether or not other disorders were present. When the psychiatric
evaluation indicated ADHD, the QEEG was equally likely to be positive regardless
of what other psychiatric conditions were diagnosed. Similarly, when ADHD
was not diagnosed, the likelihood that the QEEG marker was negative did not
depend on what other conditions were present. Thus, the classification
accuracy of QEEG as a diagnostic test for ADHD was not influenced by the
presence or absence of other psychiatric conditions.
Summary and Implications
I believe these findings are very important. One clear implication
is that results from behavior rating scales must be used cautiously in ADHD
evaluations. Making diagnostic decisions based on counting symptoms
and/or determining whether a child's rating scale results falls in a clinically
elevated range for ADHD will lead to high rates of misdiagnosis in comparison
to what would emerge from a comprehensive psychiatric evaluation. In
particular, data from this study suggests that many children who do not truly
have ADHD would be erroneously diagnosed with the disorder.
I should emphasize that ADHD evaluation guidelines from the American Academy
of Pediatrics and the American Academy of Child and Adolescent Psychiatry
clearly indicate that rating scales should never be used in isolation to
diagnose an individual with ADHD. Thus, using rating scales in this
way is inconsistent with best practice guidelines. However, given the
limited time available in many primary care settings to conduct comprehensive
evaluations, it would not be surprising if rating scale results are sometimes
given greater emphasis than is recommended.
This is where QEEG results can be so helpful. In regards to matching ADHD
diagnostic decisions that result from a comprehensive evaluation, this test
performed quite well - overall accuracy rates were nearly 90%. The
false positive rate of only 6% means that few children and adolescents for
whom ADHD is ruled out by a comprehensive psychiatric exam would be diagnosed
if QEEG findings were used to make the decision. This is a striking
contrast to false positive rates that exceeded 80 % for some of the rating
scale measures. Although adjusting how rating scale data is used to
make decisions about ADHD might improve classification accuracy somewhat,
it is difficult to imagine that overall accuracy rates would ever approach
that found for QEEG.
It is important to underscore that despite the strong results found for QEEG,
this tool is not a substitute for a comprehensive diagnostic exam and should
not be used as a stand alone test for ADHD. One essential reason for
this is that diagnostic evaluations for ADHD should go beyond simply deciding
whether ADHD is present and gather other information that is critical for
developing an optimal treatment plan. While QEEG may help with the
former, it does not contribute to the latter, beyond identifying individuals
for whom medication treatment would be an appropriate option to consider.
I have heard experienced users of QEEG discuss that other data from the procedure
can be useful in more expansive treatment planning, but I am not familiar
with research that supports this broader use.
Given this limitation, what value would there be to routinely incorporating
QEEG into ADHD diagnostic evaluations. Several things come to mind
including the following:
1. In primary care settings where a comprehensive psychiatric exam can be
difficult to provide, results from a 30-40 minute QEEG procedure can identify
with reasonably high accuracy individuals for whom ADHD is likely to be an
2. Because false positive rates are so low, QEEG could reduce the number
of individuals who are perhaps inappropriately treated with ADHD medication
if physicians referred individuals with negative results for further evaluation.
3. In cases where parents are reluctant to pursue treatment for their child
because of concerns that objective evaluation procedures were lacking, QEEG
provides an objective biological marker of ADHD that can increase parents'
confidence in their child's evaluation.
4. For people who continue to doubt that ADHD is an actual condition with
important biological underpinnings, these findings highlight that the vast
majority of individuals meeting DSM-IV criteria for ADHD have a distinctive
pattern of brain EEG activity.
Overall, findings from this carefully conducted study make an important contribution
to documenting the utility of QEEG as an objective test to assist in the
diagnosis of ADHD. If this procedure were to become more widely used,
these data suggest that the number of children and adolescents who are inappropriately
diagnosed and treated for the disorder would diminish substantially.
(c) 2013 David Rabiner, Ph.D.
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