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Wednesday 5 October 2011


ADHD: Differential Diagnoses, Comorbidity, and Prognosis

By Leslie E. Packer, PhD, 
This article last updated July 2010


Using the current diagnostic system in the DSM-IV-TR, clinicians talk about three different subtypes of ADHD: (1) children who are primarily inattentive, (2) children whose main problem is impulsivity-hyperactivity, and (3) children who have both inattention and impulsivity-hyperactivity problems to a significant degree (the combined subtype).

The current diagnostic DSM-IV-TR criteria for ADHD have been controversial on a number of levels and some changes are being considered for the DSM-5. It is unlikely that the revised criteria will resolve all controversies, however. Although some people have questioned whether ADHD should really be considered a disorder (cf, the discussion by William Carey, M.D., and papers by Rubia or Shaw et al. (2007) on ADHD as a maturational delay), most healthcare professionals consider ADHD a neurological disorder. Research such as that of Qiu et al. finding volumetric differences and abnormal shape of basal ganglia structures in boys diagnosed with ADHD are offered as support for that position.

Although anyone who has parented, taught, or worked with children and teens diagnosed with ADHD is fully aware that many of these children have extraordinary flashes of brilliance, creativity, and an intensity to life that we can only marvel at, there are so many grim statistics on the outcomes for children and teens diagnosed with ADHD that regardless of whether one believes it is a neurological disorder or a condition that reflects variations in normal temperament, I think it is important to be aware of the risks so that they can be addressed.

A Picture Speaks 1,000 Words

Many people erroneously assume that if the child is hyperactive, the brain must also be overactive. This is not the case, however, as this brain scan from the research of Dr. Zametkin (1990) shows:

In the image above, high levels of glucose metabolism are indicated by red, orange, and yellow, while lower levels of are indicated by greens and blues. Glucose metabolism is an indication of energy or mental activity. When given a problem to think about, the “normal” control subject’s brain indicates energy being used to think about the problem posed, but the ADHD subject’s brain shows little activity. It would be interesting to see what would happen if the question or problem happened to be of especial interest to the individual with ADHD, but that was not explored in this study.

The image suggests a useful way of thinking about ADHD as “Who turned out the lights?” (Packer, 1999, unpublished). If you think of the brain of an individual with ADHD as usually being in a “browned-out” state, it becomes somewhat evident why they might have trouble sustaining their focus. It also helps to explain why responses and behavior may be disinhibited: when there is too little activity, the “brakes” that would inhibit behavior are underperforming, leading to more behavior that would otherwise be inhibited.

Do such data show that ADHD is strictly a biological problem? No. ADHD also appears to be influenced by environmental factors such as home environment, classroom structure, and peers.  

Kieling, Goncalves, Tannock, and Castellanos (2008) provide a review of the neurobiology of ADHD and the potential role of environmental factors.

Saying that ADHD is influenced by environmental factors such as home environment or classroom environment does not mean that ADHD is caused by faulty parenting or education. Rather, it means that we have an opportunity to make things better or worse. Certainly biological parents are responsible, on some level, for their child – particularly when we consider the genetic research that shows that ADHD is highly heritable. Does this mean that the parents “caused” their child’s ADHD? Yes, on some level, but only in the same sense that we say a parent “caused” their child’s eye color, height, intelligence, or athletic or artistic ability.

ADHD takes a toll on the parents, and when the child has inherited ADHD from one or both parents, the parents may have less than ideal parenting styles because of their own ADHD symptoms. As consequences, they may not be able to provide the structures and support the child needs, or they may react poorly to the child’s symptoms, thereby worsening the child’s situation, marital discord, and entire family functioning. A 2008 study by Wymbs et al. found that the divorce rate among parents of children aged 8 or younger with ADHD was significantly higher than the divorce rate in the general population. But it is not just the caregivers who are affected by the child’s symptoms. Recent research also suggests that non-ADHD siblings may also suffer academic impact due, perhaps, to the ADHD child demanding so much time and attention from the parents. A number of studies have found that parent training that includes teaching parents how to structure the home, how to arrange consistent and effective contingencies for behavior and how to engage the child in problem-solving is an effective psychosocial intervention as part of a comprehensive treatment program.

Schools also have the potential to ameliorate or exacerbate a child or teen’s symptoms. In some cases, children who function well outside of school are inappropriately diagnosed as ADHD simply because they do not well in the type of structure and under the conditions of the classroom or school setting. A diagnosis of ADHD should not be made if functioning is only impaired in one of the three main settings: home, school, and community. If problems occur in only one setting, other factors may be responsible.

Diagnosing ADHD

ADHD is characterized by either inattention and/or hyperactivity-impulsivity. There is a veritable “Chinese menu” for determining whether a particular patient meets the diagnostic criteria for ADHD, and if so, for which subtype. As a result, two individuals could both be diagnosed with ADHD and yet have significantly different features or challenges.

In the United States, mental health professionals use the DSM-IV diagnostic criteria* while in Europe, mental health professionals generally use the ICD-10 diagnostic criteria. A variety of ADHD screening tools are listed on Neurotransmitter.net.

Note that in the American criteria, a child need not have both hyperactivity-impulsivity and inattention. It is possible to be diagnosed if inattention is the primary or sole problem. Although many children and teenagers will meet criteria for both inattention and hyperactivity-impulsivity (i.e., they will meet diagnostic criteria for the “combined” subtype), keeping the different subtypes (primarily inattentive, primarily hyperactive-impulsive, or combined) in mind is helpful.

The diagnostic criteria include other conditions that must be ruled out before a diagnosis of ADHD is made. Because there are many other possible explanations for inattentive or hyperactive-impulsive behavior, the professional needs to collect information from multiple sources of information. A few of the many other conditions that produce behavior patterns or symptoms that might at first blush appear to be ADHD include:

    A learning disability that leads to poor performance in school, frustration, and a behavior pattern where the child seems to stop paying attention or “gives up” listening to the teacher;
    Attention lapses caused by petit mal seizures;
    Attention lapses caused by obsessive thoughts or silent compulsive rituals;
    A middle ear infection causing an intermittent hearing problem that interferes with the child’s ability to respond to orally presented requests or material;
    Disruptive or unresponsive behavior due to anxiety, depression, or bipolar disorder;
    Environmental factors or stressors that lead to restlessness or inattention (such as divorce, problems on the job, etc.)

A difficult differential diagnosis question is whether a child has ADHD+Oppositional Defiant Disorder or Bipolar Disorder, or both. When a child or teen presents with a more chronic and severe irritability in the presence of signs of ADHD, then even if they have “rages,” that does not mean that they have Bipolar Disorder.  The DSM-5 task force has proposed a new diagnosis called Temper Dysregulation with Dysphoria that they think may be more appropriate.

In addition to some of the differential diagnoses mentioned above, Many sources on ADHD do not list another differential diagnosis that I would include: giftedness. On this web site, you will find some information on differentiating between ADHD and giftedness. Although it is certainly possible that some children and teenagers have both ADHD and giftedness, in some cases, gifted children are being misunderstood — and misdiagnosed — as having ADHD.

Although a variety of professions may be licensed to diagnose ADHD, my firm recommendation is that the diagnosis not be made unless the child has been fully evaluated by a developmental pediatrician, a board-certified neurologist, or a child and adolescent psychiatrist who can rule out other medical problems that may mimic the symptoms of ADHD.

In another section on this site, a condition known as Executive Dysfunction is described. If you are already familiar with EDF, you will have noted that many of its symptoms described sound remarkably like the inattentive criteria in the DSM-IV criteria for ADHD. Specifically, the following signs or symptoms of “inattention” may also indicate executive dysfunction:

    Often fails to give close attention to details or makes careless mistakes in schoolwork, work, or other activities;
    Often has difficulty sustaining attention in tasks or play activities;
    Often does not follow through on instructions and fails to finish schoolwork, chores, or duties in the workplace (not due to oppositional behavior or failure to understand instructions);
    Often has difficulty organizing tasks and activities;
    Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (such as schoolwork or homework);
    Often loses things necessary for tasks or activities (e.g., toys, school assignments, pencils, books, or tools);
    Is often easily distracted by extraneous stimuli

In order to clarify diagnostic issues, a neuropsychological assessment may be helpful or necessary.

It is important to note that although there is significant overlap between executive dysfunction and “inattention” as described in the DSM-IV, not all individuals with ADHD have EDF, and EDF occurs comorbid with a number of conditions or disorders, not just ADHD.

EDF is discussed in its own section of this web site.

What Conditions are Associated with ADHD

When two conditions occur together in the same individual, we say they are “comorbid.” If the two conditions tend to occur together more often than would be expected by chance in the population, we say that the conditions are “associated” (with each other).

Certain conditions tend to occur in children and teens with ADHD more than you would expect to see by chance, and some sources have estimated that approximately 2/3 of children with ADHD will have one or more comorbid conditions during their lifetime. In clinical settings, the comorbid conditions most commonly reported in ADHD are:

    Oppositional-Defiant Disorder
    Conduct Disorder
    Substance Use Disorder
    Developmental Coordination Disorder
    Learning disabilities
    Memory deficits, especially working memory
    Processing speed deficits
    Executive Dysfunction
    Sleep disorders
    Sensory issues
    Handwriting problems and fine-motor control problems
    Enuresis (bedwetting)
    Anxiety Disorders
    Mood disorders such as Depression and Bipolar Disorder
    Obsessive-Compulsive Disorder
    Accidents and Injuries
    Internet “addiction”
    new-onset pediatric epilepsy and celiac disease.


One of the more intriguing findings has been the relationship between inattention-impulsivity, early peer relationships, and the emergence of conduct disorder. Snyder, Prichard, et al. (2004) found that with boys, the inattention-impulsivity was related to conduct problems but the relationship was mediated or modulated, in part, by peer rejection and involvement in coercive exchanges with peers. For girls, the relationship between inattention-impulsivity and conduct disorder was not as clearly mediateverd by peer interactions, although peer difficulties did affect the emergence of conduct problems. Their study not only elucidates the complex relationship between gender, inattention-impulsivity, peer difficulties, and conduct disorder, but it suggests that we need earlier interventions to address any emerging peer difficulties.

In adults with ADHD seen in clinical settings, Antisocial Personality Disorder, substance abuse, learning disabilities, and mood disorders are often comorbid with the ADHD. Other personality disorders are also more common in adults with ADHD than in non-ADHD adults: histrionic, passive-aggressive, and borderline personality disorders.
Outcomes and Prognosis

Up to 85% of children with ADHD may continue to have problems in adolescence. Peer problems that are noted in childhood may persist, and if the ADHD symptoms also persist into adolescence, the peer impact is even more significant. Adolescents who have a history of ADHD in their childhood may be more likely to have fewer friends, experience greater peer rejection, and have friends who are less involved in conventional activities.

The statistics, culled from a number of studies, are somewhat alarming:

    31% run away from home (vs. 16% of non-ADHD peers)
    39% carry a weapon (vs. 11%)
    22% commit assault with a weapon (vs. 7%)
    22% are arrested for a felony (vs. 3%)
    38% have teen pregnancies (vs. 4%)

The estimates of the percent of children with ADHD who continue to have problems in adulthood vary widely, but current studies indicate that symptoms will persist for a sizable percentage.

By their mid-twenties, when compared to non-ADHD peers, those with ADHD have completed less schooling, tend to hold lower-ranking occupations, and continue to suffer from poor self-esteem and social skills deficits. In addition, they are more likely to exhibit an antisocial personality and (perhaps) a substance use disorder in adulthood. For example, Fischer, Barkley, et al. (2002) compared young adults who had been diagnosed with ADHD as children to community controls (CC). They found that the ADHD group had significantly higher rates of non-drug psychiatric disorders, were more likely to have ADHD as young adults than the CC group, and had significantly higher rates of major depressive disorder and personality disorders (histrionic, antisocial, passive-aggressive, and borderline personality disorders). Consistent with findings of other researchers, their data indicated that conduct problems in adolescence contributed significantly to the risk of personality disorders, two of which significantly increased the risk for major depression.

In the discussion above, general patterns were described without respect to subtype of ADHD. Do different subtypes have different outcomes as adults? Murphy et al. (2002) addressed that question by comparing adults with ADHD-combined type (ADHD-C) to adults with ADHD-inattentive type (ADHD-I) and community controls (CC). Both ADHD groups had completed less formal education than the CC group, were less likely to have graduated from college, and were more likely to have received special educational placement in high school. Both groups also reported more alcohol dependence/abuse, more dysthymia, more cannabis dependence/abuse, and more learning disorders, as well as greater psychological distress. Elsewhere on this site, in the article, “ADHD and Safety,” site visitors can also learn about the increased rate of accidents (pedestrian and vehicular) and the increased risk of more serious injuries in both children and adults with ADHD.

But how did the two ADHD groups fare when compared to each other? For the measures employed, the two groups differed in only a few respects: The ADHD-C were more likely to have oppositional behaviors, interpersonal hostility, paranoia, and some history of attempted suicide. They were also more likely to have been arrested than the ADHD-I group. Their findings suggest that the impulsivity of the Combined subtype predicts a poorer outcome as an adult, particularly if there are also conduct problems in childhood. But a more recent study suggests that those with more severe problems of inattention during childhood may be significantly more likely to report frequent episodes of drunkenness, higher alcohol problem scores, and a greater likelihood of substance abuse as teenagers and that impulsivity-hyperactivity was not associated with teenage substance abuse.

The research described above does not tell the whole story of the ADHD child’s adult outcomes, however. Mannuzza and Klein (2000) reported that nearly all of the children followed into adulthood were gainfully employed, and some had achieved a higher-level education (such as a Master’s degree or enrollment in medical school) and occupation (e.g., accountant, stock broker). For the studies they reviewed, the authors found that a full two thirds of the children showed no evidence of any mental disorder in adulthood. They conclude that although ADHD children, as a group, fare poorly when compared with their non-ADHD peers, ADHD does not preclude attaining high educational and vocational goals, and that most children no longer exhibit clinically significant emotional or behavioral problems once they reach their mid-twenties. Their data were not confirmed by subsequent studies reporting high rates of persistence of ADHD symptoms into adulthood with significant functional impairment in adulthood. Although more data are needed on these important questions, it seems clear that we need to recognize ADHD early and implement  a multifacetted treatment programme and support early.


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