The diagnosis of ADHD is based almost entirely on history obtained from the patient, parents, teachers and other people who know the child well. There is no blood test, imaging study or computerized test that can be relied upon to accurately make the diagnosis of ADHD.
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Part of this history can be obtained by using standardized ADHD questionnaires, such as the Conners or Vanderbilt forms. It is a mistake, however, to rely substantially or entirely on these forms to rule the diagnosis in or out.
Many professionals in the field believe that children and adults are frequently poorly evaluated and misdiagnosed as having ADHD. The root of the problem lies in the fact that making the diagnosis involves such a careful history and simply takes an amount of time that many practitioners are unable to provide. Too often, the busy pediatrician or family doctor makes this diagnosis in one or two 10- to 15-minute visits, relying almost entirely on a quick scoring of one of the above forms. A complete evaluation should take one to two hours and include a careful history, a directed physical exam, as well as evaluation of the Conners or Vanderbilt forms and other psychological or psychoeducational evaluations.
The main reason it is necessary for the physician to be thorough is that so many conditions can be misdiagnosed as ADHD. Anxiety Disorders including PTSD can present with ADHD symptoms. The gifted child can appear to have ADHD, acting out due to boredom. As mentioned previously, learning disabilities can present as ADHD. Even depression can look like ADHD in some children. Even more confusing, anxiety, depression and learning disabilities can be co-conditions with ADHD, meaning that both diagnoses are accurate.
Another interesting fact about ADHD: It is usually assumed that once a diagnosis of ADHD is made a child will continue to have that diagnosis for a long time, if not the rest of his or her life. Yet careful study shows this to be untrue. In one study, children who were carefully diagnosed as having inattention problems by a teacher in one grade were reassessed the following year. Less than 50 percent of those children were thought to have inattention problems by the next teacher. It is not totally clear why this happened, but there are a couple of reasonable explanations. First, the standardized forms that teachers fill out are completely transparent. It is entirely obvious which boxes to check to ensure an ADHD diagnosis. If a teacher or parent feels ADHD is the problem, they can fill out the form in such a way as to confirm it, with biased responses occurring either consciously or unconsciously. Also, what may seem an abnormal behavior to one parent or teacher may seem entirely within normal limits to another. More importantly, perhaps, how a child behaves in school can be highly dependent on the type of classroom it is. In a loud, unstructured classroom the child may exhibit significant ADHD symptoms, while that same child can do well in a quiet, supportive and structured atmosphere. See the “continuum” of ADHD discussed in the Overview article. Those in the risk group may easily fall on either side of the ADHD line, depending upon the home or school environment.
There are a couple of interesting adjunctive tests that can help with the diagnosis of ADHD. The first are computerized tests of attention. These are usually done by psychologists and involve patients sitting at a computer and being asked to do things like press a button every time the letter A flies across the screen. They are tested on how many times they press the button at the correct time, how many times they fail to do this and how many times they press the button at the wrong time. These tests can be useful as part of the diagnostic workup, but cannot be relied upon by themselves.
An even more interesting and newer test looks at brain wave ratios. It has been established that children with ADHD usually have an abnormal brain wave pattern, having too low a ratio of beta waves (associated with alert, focused attention) to theta waves (associated with spacing out). This can be easily measured by simply attaching a couple of sensors to the scalp, much like a simplified EEG. Studies have shown that this test could predict with about 90 percent accuracy whether children would be diagnosed with ADHD. In 2014 the FDA approved this brain wave test, called the NEBA, as a reasonable tool that could be a part of the diagnosis of ADHD. The FDA did not state whether it was a necessary test nor a stand-alone tool for diagnosis of ADHD.
The bottom line is that the diagnosis of ADHD should be done with care and consideration and should also be revisited on a regular basis over time to make sure it is still accurate.