ADHD as a Diagnostic Chameleon: Developing a Systematic Approach to Differential Diagnosis

February 8, 2008
DIALOGS ADHD, December 2007, Volume 5, Issue 1

ADHD is a common presentation in all clinical settings. However, data shows that ADHD is underrecognized in adults.1 Why is this? Remember the old adage, "Out of sight, out of mind?" If ADHD is not thought of as a possibility in adult patients, is it more likely to be missed?

DHD is a common presentation in all clinical settings.

However, data shows that ADHD is underrecognized in adults.1 Why is this? Remember the old adage, “Out of sight, out of mind?” If ADHD is not thought of as a possibility in adult patients, is it more likely to be missed? When ADHD in adults presents with co-morbidities, does the disorder become a “diagnostic chameleon”?

The answer to both questions, based on our reading of the literature, and our combined four decades of clinical experience, is a resounding yes. ADHD is indeed quite frequently missed, and there is a clear and pressing need for clinicians to openly discuss differential diagnosis difficulties and come up with a game plan to meet the needs of patients with ADHD. This tutorial is designed to provide a scientific as well as a practical grounding in the issues germane to ADHD in adult patients, particularly if these patients present with one of these common co-morbidities:

• Mood disorders (major depression and bipolar disorder)

• Anxiety disorders (generalized anxiety disorder, social anxiety disorder, etc)

• Alcohol and substance abuse disorders


Differential diagnosis is important to ensuring good outcomes. The topic of co-morbidities is very important to the issue of differential diagnosis. In clinical practice, most agree that co-morbidities tend to be the rule, not the exception. We strongly recommend you appreciate the importance of co-morbidities in ADHD because many patients tend to present with “masked” ADHD, with the co-morbidity (such as an anxiety or mood disorder) taking center stage and making it easy to miss the ADHD if a systematic diagnostic approach is not undertaken. To substantiate this point, figure 1 highlights several conditions that are frequently co-morbid with adult ADHD.

Clinicians must continue to screen for ADHD if a patient presents with co-morbidities (eg, major depression, anxiety disorders, alcohol and substance abuse disorders). If a patient presents with major depression or anxiety difficulties, even upon remission of symptoms, clinicians must maintain a high degree of suspicion and routinely screen for ADHD. Our job is somewhat like that of an archeologist, continually sifting through sand searching for objects of importance.

Remaining vigilant in our search for symptoms of ADHD is clinical wisdom and is worth repeating. Consider the lifetime prevalence of co-morbid conditions in adult populations with ADHD highlighted in figure 2.

Anxiety disorders are the most common conditions affecting the United States population.2 In our practice, we most frequently see generalized anxiety disorder, social anxiety disorder and PTSD. As figure 2 illustrates (previoius page), adult ADHD is quite co-morbid with anxiety disorders. To get a more accurate clinical picture, let’s broaden the boundaries beyond anxiety disorders and take into consideration other co-morbidities outlined in figure 3.

We must not stop short when taking care of patients. Based on this data, we must screen for ADHD. These graphics illustrate the urgent need to proactively and routinely screen patients for the presence of ADHD. Complicating ADHD’s clinical picture is the fact that as many as 50% of individuals with the disorder will meet the criteria for at least one co-morbid psychiatric condition.3-5 In children, these co-existing conditions include learning disabilities, anxiety disorders, mood disorders, autism spectrum disorders, and other disruptive behavioral disorders, such as oppositional defiant disorder and conduct disorder. These disorders have an obvious impact on children’s abilities to function adequately in their academic, social, and family environments and, in combination with ADHD symptoms, often lead to adverse life outcomes and increased utilization of mental health, academic, and criminal justice system resources.

In adolescents and adults, mood and anxiety disorders, as well as substance abuse disorders, commonly co-exist with ADHD.6 Mood disorders, anxiety, substance use, and intermittent explosive disorder have been found to be 1.5 to 8 times more likely in adults with ADHD than in those without, and associated problems of frequent job changes, unemployment, and criminal arrests were found to be more common in this population as well.3,7 Studies of driving behavior also indicate that adults with ADHD incur higher rates of accidents on the highway and motor vehicle—associated injuries.8 The fact that ADHD is likely to occur with other psychiatric disorders adds to the clinical complexity of both diagnosing and treating the disorder and amplifies the potential for adverse life outcomes.

Comprehensive pharmacoeconomic data are lacking on

ADHD’s impact in adulthood, but indirect indicators—such as the

increased rates of criminal involvement, substance abuse, and psychiatric

co-morbidities, along with driving data—would suggest

that ADHD is a costly disorder. Numerous studies have documented

the high societal costs of depression, anxiety, and substance use

disorders but have ignored the impact of co-morbid ADHD.9-11

Increased or Unnecessary Cost to Patients and Society

Data for healthcare use and cost-of-illness in adults with ADHD is lacking.12-14 The persistent nature of ADHD wouldsuggest,

however, that adults with the disorder, like children, have higher healthcare use and costs than people without the disorder. Little, too, is known about the social cost of ADHD, but if left untreated, the effect of the disorder may be substantial. For example, the prevalence of ADHD in male prisoners has been estimated to be 25%, which is five times that of the

general population.15

Functional Impairments (Work, Academic, Family, and Social)

Overlooked or misdiagnosed ADHD can result in serious functional impairments for the patient. Barkley and colleagues have found that people with ADHD frequently get fired, change jobs, and have lower job performance evaluations than people without ADHD.16 No clinician or patient is immune from the consequences of missing a diagnosis of adult ADHD.

Diagnostic Issues and Challenges in Adult ADHD

Diagnosing co-morbid ADHD in adult patients with anxiety disorders, mood disorders, and/or alcohol/substance abuse disorders is challenging due to the lack of systematic screening for all patients as part of routine care, and failing to consider ADHD as a possible diagnosis. Distractibility as a stand-alone symptom may alert clinicians to a variety of different DSM-IV-TR diagnoses or distractibility may mean absolutely nothing. Figure 4 (previous page) provides an illustration of distractibility as a roadmap to multiple disorders. Clinicians who do not currently screen patients may find it difficult to change existing practice habits. Nevertheless, incorporating screening into routine clinical practice is a necessity and screening tools for adult ADHD are available.

Screening for Adult ADHD

One of the most striking, and useful developments in the field of screening has been the development of the six-item instrument called the Adult ADHD Self Report Scale (ASRS), version 1.1 (figure 5, previous page). It was developed under the auspices of a WHO work group and is designed to screen for adult (18 years and older) ADHD in community samples. The screener takes less than five minutes to complete and can provide very useful supplemental information as we screen all our patients for adult ADHD. The ASRS is, in our opinion, an efficient and effective screener for adult ADHD. In our clinical practice, we feel the sensitivity and specificity of ASRS has been quite good. The only cautionary note regarding screeners is to be watchful for false positives. With that said, screeners are a great safety net to help capture important clinical information. Screeners serve as red flags to alert clinicians to the possibility that something is going on. We strongly recommend the use of ASRS in all patients, even if the presenting symptoms initially suggest an anxiety disorder, mood disorder, or alcohol or other substance abuse disorder. Remember: screeners work best if we routinely use them in all patients. Because ADHD in adults is quite common, we confidently recommend the routine use of ASRS in all clinical settings.

A Systematic Approach to Discovering Co-Morbid ADHD

It is important to create a step-by-step paradigm to accurately assess patients. One such paradigm that we use in our clinical practices is illustrated in figure 6 (previous page). This decision tree offers clinicians a systematic pathway to identifying diagnoses. Consider the decision tree as a roadmap to discovering co-morbid ADHD. Clinicians must remember to screen ALL patients for ADHD who present with a diagnosis of any mood disorder, anxiety disorder, or alcohol/substance abuse disorder. As discussed in the previous section, the ASRS is an excellent screener for adult ADHD. If the ASRS is negative, ADHD is an unlikely co-morbidity. However, if the ASRS is positive, the clinician must determine the following:

• Has the patient met 6 of 9 of the DSM-IV-TR criteria for either or both inattentive or hyperactive/impulsive symptoms?

• Is age of onset before age 7?

• Is impairment present in at least two settings?

If yes, ADHD is a likely diagnosis. This type of systematic approach offers clinicians a great safety net against missing critically important pieces of information. As a footnote, screeners are not diagnostic but their suggested use as an addition to routine clinical practice is strongly recommended.


ADHD does indeed qualify as a “diagnostic chameleon.” However, the clinician who employs a systemic approach to routine screening and co-morbidity detection, will surely be successful in improving patient outcomes. Indeed, the diagnosis of ADHD is not always clear at first, but the rewards for patients when an accurate diagnosis is made are so great that we feel compelled to urge all our colleagues to strive to maximize their screening efforts and to utilize the decision tree we and others recommend. While it is true that overlapping symptoms between many psychiatric co-morbidities can lead to confusion, utilizing the “pyramid of information” illustrated in figure 7 can lead to enhanced detection and outcomes for patients with adult ADHD. If all of these seven steps are undertaken in a systematic and deliberate fashion, you can rest assured that you have offered your patient the very best of clinical services.

Saundra Jain, PsyD, is the Executive Director of Mental Health Educational Initiative, an organization that provides educational services to mental health professionals and patients. She also maintains a fulltime private psychotherapy practice, offering services for a wide range of mental health issues.Rakesh Jain, MD, MPH, is Assistant Clinical Professor of Psychiatry at the University of Texas Medical School in Houston. He is also Director of Psychiatric Drug Research for R/D Clinical Research at Lake Jackson, TX.