Is ADHD Always a Childhood Onset Disorder?
by Joseph Biederman, MD – August 4, 2016
Recent population based studies raise the intriguing question as to whether adult ADHD is always preceded by childhood onset of symptoms or can develop anew in adult life. From Brazil, one group argues that child and adult ADHD are “distinct syndromes”; from the United Kingdom (UK), another group states that adult ADHD is “more complex than a straightforward continuation of the childhood disorder” and from New Zealand (NZ), a third group claimed that adult ADHD is “not a neurodevelopmental disorder”.
In each study, adult onset ADHD refers to cases in which full-threshold ADHD had not been diagnosed by the investigators at prior assessments. In the NZ study, compared with controls, the adult onset ADHD group had more teacher-rated symptoms of ADHD, more conduct disorder (CD) in childhood and were more likely to have had a combined parent/teacher report of ADHD symptom onset prior to age 12. (DSMV recognizes onset of ADHD until the age of 12.) Likewise, the adult onsets in the UK study had high rates of ADHD symptoms, CD and oppositional defiant disorder (ODD) in childhood. Thus, many “adult onsets” of ADHD cases appear to have neurodevelopmental roots.
Because population studies use non-referred samples, those being diagnosed may not be self-aware of their symptoms, which increases the risk of false negatives. In population studies the ability of the subject to report on his or her own symptoms is critical since it requires insight and self awareness. It has been well documented that youth with ADHD are very poor reporters of their own symptoms. Such difficulties can certainly extend to adult years. Consistent with this idea, another longitudinal study found that current symptoms of ADHD were under-reported by adults who had had ADHD in childhood and over-reported by adults who did not have ADHD in childhood.4 Thus, the UK, Brazilian and NZ studies may have underestimated the persistence of ADHD and overestimated the prevalence of adult onsets. In contrast, self awareness is not an issue for subjects referring themselves to clinical care since, by definition, it is their self awareness that brings them to the clinic.
These reports do very little to help clarify whether these “adults” do not recall childhood symptoms, are unable to report on them, or are unable to distinguish onset of symptoms form onset of symptoms-associated impairments that may account for the different ages of onset. In these cases, the onset of symptoms and impairment could be separated by many years, particularly among those with strong intellectual abilities and those living in supportive, well-structured childhood environments. Such intellectual and social scaffolding would help ADHD youth to compensate in early life, only to decompensate into a full ADHD syndrome when the scaffolding is removed.
Such an interpretation would suggest that the etiology of ADHD leads to a wide variability in age at onset of initial symptoms, symptoms exceeding diagnostic threshold and impairment arising from those symptoms. Such variability is accepted for many other medical disorders. It is also consistent with the idea that ADHD is the extreme and impairing tail of a continuum. This view of posits that ADHD symptoms and ADHD impairment emerge due to the accumulation of environmental and genetic risk factors. Those with lower levels of risk at birth will take longer to accumulate sufficient risk factors and longer to onset with symptoms and impairment. Yet, because these effects are multifactorial, there is no clean separation of etiologic factors in people above and below a certain age.
In this context it is important to remember that the age of onset of ADHD of 12 years proposed in DSM-V, while an improvement from the previous age of onset of 7 years, is still completely arbitrary, creating the immediate dilemma on how to diagnose patients who have an onset of symptoms after 12 years of age. Such a scenario may suggest that ADHD may be a disorder with a continuum of ages of onset, with some subjects starting their symptoms earlier while others later.
These concerns do not argue against the existence of adult onset ADHD or the idea that it is a clinically relevant syndrome. In fact, as a group, the adult onset cases showed significant functional impairments. Moreover, some of the studies ruled out the idea that adult onset ADHD is a misdiagnosis of another disorder. Further support for the validity of adult onset ADHD comes from a study of referred adults who retrospectively reported childhood symptoms 5. Based on clinical features and familial transmission, that study concluded that onsets of ADHD in late adolescence and early adulthood were valid.5
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