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Early vs. Late Onset of ADHD Symptoms: Does it Matter?
One controversial aspect of current diagnostic criteria for ADHD is the requirement that in addition to displaying a certain number of inattentive and/or hyperactive-impulsive symptoms, some of these symptoms must have been present and caused some impairment prior to the age of 7. (For a complete discussion of current diagnostic criteria, click here.
This age-of-onset criteria was included in DSM-IV (the diagnostic manual for all psychiatric disorders, including ADHD) based on findings that most children with ADHD first exhibited symptoms in early childhood, and in response to concerns that when ADHD symptoms appear after age 7, they often may be due to school failure or stress rather than to ADHD. Thus, by requiring ADHD symptoms to have been evident and causing impairment before the age of 7 for the diagnosis to be appropriate, it was hoped that children whose symptoms first emerged at later ages for a variety of other reasons would not be misdiagnosed as having ADHD.
This age-of-onset criteria assumes that there is a meaningful difference between children whose ADHD symptoms emerge relatively early in life from those whose symptoms first become evident later on. Several ADHD experts (in particular, Dr. Joseph Biederman and Dr. Russell Barkley) have questioned the validity of this assumption and suggested that the age 7 cutoff is arbitrary and not based in science. As a result, there are concerns that this may actually deny diagnoses and services to youths who suffer from ADHD-related difficulties.
For example, a child who met all symptomatic criteria for ADHD except for the age-of-onset criteria currently would not be given the diagnosis and could thus be denied access to educational services that would otherwise be provided. In addition, treatment options typically considered for a child with ADHD might be discarded. Clearly, it is potentially problematic to have this unsubstantiated age-of-onset cutoff in the official diagnostic criteria for ADHD. Research to establish the validity of this requirement is needed.
A study published in a recent issue of the Journal of the American Academy of Child and Adolescent Psychiatry offers the best data currently available on this important issue (Willoughby, M.T., et al., 39, 1512-1519, 2000). Participants in the study were part of a large study designed to determine the prevalence of a variety of childhood psychiatric disorders and the impact of different disorders on children and their families.
A representative sample of 4500 students, grouped by ages 9, 11, and 13, was recruited from 11 counties in western North Carolina. Parents completed an initial screening instrument designed to detect child behavior problems. When this score exceeded a pre-determined cutoff, these parents and children were invited to participate in a more detailed assessment that involved thorough psychiatric interviews of both parents and children over a 4–year span. In addition, a sample of children whose behavior problem screening score fell below the cutoff was recruited to serve as comparison subjects.
The authors identified children who met symptomatic criteria for ADHD based on the results of an extensive parental interview. Parents also provided information about the age at which their child’s symptoms first became evident. These ADHD participants were then divided into 6 mutually exclusive groups:
- Those with the inattentive subtype of ADHD with onset of symptoms before age 7;
- Those with the inattentive subtype of ADHD with onset of symptoms after age 7;
- Those with the combined subtype of ADHD with onset of symptoms before age 7;
- Those with the combined subtype of ADHD with onset of symptoms after age 7;
- Those with the hyperactive-impulsive subtype of ADHD with onset of symptoms before age 7;
- Those with the hyperactive-impulsive subtype of ADHD with onset of symptoms after age 7;
Note: The inattentive subtype refers to children showing large numbers of inattentive symptoms but relatively few hyperactive-impulsive symptoms. The exact opposite is true for children with the hyperactive-impulsive subtype, while children with the combined subtype display high numbers of both types of symptoms. A seventh group was comprised of children who never met symptomatic criteria for ADHD. They served as a comparison group.
Once these groups were identified, children with each subtype of ADHD whose symptoms emerged either before or after the age of 7 were compared to one another, and to children without ADHD symptoms. Children were compared on a variety of different dimensions, including: the number of settings in which they were currently struggling, the presence of other psychiatric problems in addition to ADHD symptoms, if they had required mental health services during the past 3 months, and the degree to which their symptoms were adversely affecting their parents.
If the age at which ADHD symptoms first emerge is important for making valid diagnoses of ADHD, then one would expect children in the early vs. late-onset groups to differ on these factors. However, if there were no differences between children in the early vs. late-onset group, the utility of including age of onset in the diagnostic criteria would be questionable.
Results
The authors first examined whether there were differences between ADHD subtypes in the age when parents reported the emergence of symptoms. For each subtype of ADHD, a substantial proportion of parents reported that their child’s symptoms had always been present and were unable to identify a specific year when they first emerged. This is consistent with the widely held belief that ADHD is typically evident in early childhood. Differences in the age of onset between the subtypes were also evident, with 26% of parents of inattentive youth reporting symptom onset after age 7, compared to only 13% for the combined subtype and 8% for the hyperactive-impulsive subtype. (Because symptom onset before age 7 was reported for over 90% of children with the hyperactive-impulsive subtype, comparison of early vs. late-onset groups was not possible.)
For the inattentive subtype, both early and late-onset children were more likely than comparison children to be impaired in 2 or more settings, to have used a greater number of services during the past 3 months, and to have behavioral and/or emotional problems that parents perceived as creating difficulty in their own lives. Early-onset children were more likely than comparison children to display strong oppositional behavior while late-onset children were more likely to be depressed. When early vs. late-onset inattentive children were compared to one another, they did not differ on any measure of comorbidity, impairment, or impact on parental functioning.
For the combined subtype, children in the early and late-onset groups were more likely than comparison children to be impaired in multiple settings, and to have used a greater number of services during the past 3 months. Early-onset children were also more likely to be diagnosed with conduct disorder (CD), oppositional defiant disorder (ODD), or an anxiety disorder, and their parents reported that their children’s problems caused more difficulty for their own functioning. When the early vs. late-onset groups were directly compared, the early-onset group was at an increased risk for both ODD and CD, and also appeared more likely to be depressed. They were also more likely to be receiving services and to have a greater number of negative impacts on their parents’ functioning.
Summary And Conclusions
The results of this study suggest that the age-of-onset criteria have different clinical implications depending on the ADHD subtype. For youth with the inattentive subtype of ADHD, symptom onset after age 7 occurs about one quarter of the time, and there does not appear to be any difference between early and late-onset groups in a number of meaningful clinical outcomes. In addition, children with the inattentive subtype of ADHD were clearly struggling relative to non-ADHD comparison children regardless of whether their symptoms emerged early or late. There is thus little support in these data for the requirement of an onset of symptoms prior to the age of 7 for the inattentive subtype of ADHD. In fact, one could plausibly argue from these data that such a requirement would be likely to increase the number of incorrect diagnoses by precluding a diagnosis of children with ADHD who really do have the condition.
However, a very different picture emerged for children with the combined subtype of ADHD. Among these children, those with an early onset of symptoms differed from those in the late-onset group on a number of dimensions and clearly had worse clinical outcomes. Thus, even though children in the late-onset group were struggling relative to comparison children, they were not as impaired as those whose symptoms began earlier in life. This pattern of findings suggests that the age-of-onset criteria is meaningful for the combined subtype and argues against dropping it as some have suggested. Doing so would result in the identification of a much more heterogeneous group of children as having the combined subtype of ADHD.
In regards to the clinical implications of these results, it appears that clinicians should be cautious about ruling out a diagnosis of ADHD for an inattentive child just because that child’s symptoms were not evident until later in life. This could result in a child’s inattentive symptoms being incorrectly attributed to some other condition such as a mood or anxiety disorder, and prevent the child from getting appropriate treatment. Although there are instances where a child’s inattentive symptoms reflect the impact of such conditions rather than ADHD, and clinicians always need to be vigilant about this possibility, it is the practice of ruling out ADHD as a diagnosis for inattentive children with a late onset of symptoms that is potentially problematic. (Note: In the current diagnostic system, it would still be possible to diagnose such children as "ADHD, not otherwise specified".)
Parents should be aware that the emergence of significant attention problems in older children does occur and may reflect ADHD for which appropriate treatment is required. Sometimes such symptoms do not become evident until children have moved further along in school when the academic and organizational demands increase substantially from the early elementary grades. Suddenly, a bright child who has always done well is struggling, and these problems can be wrongly attributed to laziness, lack of motivation, or an emotional problem like depression. When a parent is told that their child couldn’t have ADHD because they never showed such struggles before, attributions are likely to be made and the consequences can be quite harmful.
For a child who begins showing inattentive and hyperactive-impulsive symptoms consistent with the combined subtype diagnosis at a later age, results from this study suggest that caution in making an ADHD diagnosis is appropriate. Children with a late onset of combined symptoms seem to differ from those with earlier symptom onset, raising the possibility that their symptoms occur for reasons other than ADHD.
Therefore, when a child begins to show such symptoms at an older age, parents should raise questions if their child’s health care provider initiates traditional treatment for ADHD without first considering other explanations for their child’s symptoms.
As the authors acknowledge, there are limitations to the current study that preclude any definitive answer to the question of whether requiring age-of-onset criteria for diagnosing ADHD is appropriate, and additional work in this area is required. For example, it would be key to learn whether children with early vs. late-onset combined-type symptoms showed different patterns of response to stimulant medication treatment, different long-term outcomes, and different patterns of results on neuropsychological tests. The same would be true for children with early vs. late-onset inattentive symptoms. These kinds of data would help address this question more definitively, and would be enormously helpful in refining current diagnostic guidelines. Hopefully such information will become available shortly.
Note: This article originally appeared in Attention Research Update, an online newsletter written by Dr. David Rabiner, a Duke University psychologist and former member of CHADD's Professional Advisory Board. You can learn more about Attention Research Update and sign up for a free subscription at www.helpforadd.com.