It is fairly common that we see an adolescent or a young adult who presents to us seeking treatment for symptoms of attention deficit/hyperactivity disorder (ADHD) but who does not have a history of ADHD in childhood.
Recently, some studies that enrolled children at an early age and then followed them for many years (called “birth cohort” studies) have suggested that a “late-onset” form of ADHD also exists.
But, the authors of the paper we are discussing here argue that the birth-cohort studies previously done have many limitations. Specifically, they identified ADHD only by screening questionnaires, did not consider alternative causes of the ADHD-like symptoms, and did not obtain complete psychiatric histories.
In this study, the authors have tried to address the limitations of previous studies by looking at more detailed psychiatric assessments administered over time.
This study used the control group from a previously conducted study called the Multimodal Treatment Study of ADHD.
Participants in that control group (N=239) entered the study with no diagnosis of childhood ADHD.
They were then followed up and were assessed eight times over many years.
The mean age at the first, baseline assessment was about 10 years and at the last assessment was done at about 24 years of age.
The diagnostic evaluation used information from parents, teachers, and the subjects.
Impairment due the symptoms, substance use, and other mental disorders were also assessed. The context in which the symptoms occurred and their timing were evaluated.
To optimize sensitivity and specificity, the authors first cast an intentionally wide net for ADHD symptoms to protect against false negatives.
Then, to protect against false positives, they carefully assessed patients, required that meaningful impairment from the symptoms be present for them to be considered relevant, noted whether symptoms were present across different settings, and ruled out substance abuse or other mental disorders as the source of ADHD-like symptoms.
Out of 239 participants who did not have ADHD at baseline:
- 96 met the symptom criteria for ADHD at least one follow up assessment
- Of these 96 participants, 32 also had clinically significant impairment at the time that the ADHD symptoms were present
- Of these 32 participants, 21 had onset of symptoms in adolescence.
- Of these 21 participants, in 3 cases, the symptoms were attributed to cannabis-use disorder.
- That leaves 18 persons. Of these 18 persons, nine had a history of pre-existing or concurrent mental disorders and were reviewed by a clinical panel.
Eight experienced clinicians (three psychiatrists, five clinical psychologists) reviewed the onset and chronicity of all mental symptoms, and each voted as to whether a participant should or should not be considered to have ADHD. This was based on whether the ADHD symptoms or impairment were attributable to another disorder (e.g., effect of anxiety symptoms on concentration). Most decisions were unanimous.
Of the 9 participants with a history of pre-existing or concurrent mental disorders, the panel voted to exclude five based on evidence that symptoms better reflected another mental disorder. Of the remaining 13 (18 minus 5), only six had symptoms in more than one setting.
So, 90 out of 96 (95%) of participants who initially screened positive for ADHD symptoms were not found to have late-onset ADHD based on the more careful evaluation.
The average age at onset in the remaining six patients was about 14 years. Four of these six met symptom criteria only during the teenage years and did not receive any treatment for ADHD
Now, two things have to be noted about these six persons. Two had symptoms of ADHD that persisted into their twenties. Also, five of the six who first met full criteria for ADHD as adolescents had some symptoms of ADHD in childhood (more than most others) even if they did not meet full criteria for ADHD.
In addition to the participants discussed above in detail who had onset of ADHD-like symptoms in adolescence, another 24 participants met the full symptom and impairment criteria for ADHD for the first time after adolescence, i.e., as adults. While details are not discussed here, it should be noted that 14 of them had the impairing ADHD-like symptoms exclusively in the context of heavy substance use.
The authors note that some persons who seek treatment for late-onset ADHD may be valid cases. In a few persons, they found later onset of symptoms meeting full ADHD criteria and no alternative explanation.
But, more commonly, the symptoms suggestive of ADHD are actually due to non-impairing cognitive fluctuations, a comorbid disorder, or the cognitive effects of substance use.
They caution that if careful assessment is not done, a false positive diagnosis of late-onset ADHD can be made.
They recommend that clinicians should carefully assess impairment, psychiatric history, and substance use before treating persons who present with symptoms suggestive of ADHD but without any childhood history of ADHD.
I don’t think that clinicians are diagnosing their patients with ADHD only based on a screening questionnaire or diagnosing ADHD when the symptoms occur only during heavy substance use. Or, at least, I hope they are not.
But, I strongly agree with the authors’ warning to not diagnose late-onset ADHD without carefully reviewing the context of the symptoms and considering alternative explanations for the symptoms.
I have a lot of clinical experience treating persons with ADHD. I have seen many patients who were not impaired in childhood because they had above average intelligence and a lot of family support. So, as others have suggested, in some patients it is also possible that it is not that the ADHD had late onset but rather it became clinically impairing at a later age.