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.
Thanks
again to Cogmed for supporting
this issue of Attention Research
Update