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
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
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
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
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
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
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.
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.
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
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.