Adult-Onset ADHD Not a Continuation of Childhood Disorder?

Nancy A. Melville

July 14, 2016

Contrary to conventional wisdom, adult-onset attention-deficit/hyperactivity disorder (ADHD) is not necessarily a continuation of the childhood disorder but instead may be a separate syndrome with unique patterns of progression, two new longitudinal studies suggest.

"Above all, our findings do not support the premise that adulthood ADHD is always a continuation of childhood ADHD," write the authors of the first study.

"Rather, they suggest the existence of two syndromes that have distinct developmental trajectories, with a late onset far more prevalent among adults than a childhood onset."

The articles were published in the July issue of JAMA Psychiatry.

Findings Replicated

In the first study, investigators led by Luis Augusto Rohde, MD, PhD, a professor in the Department of Psychiatry at the Federal University of Rio Grande do Sul and director of the ADHD Program at the Hospital de Clinicas de Porto Alegre, in Brazil, evaluated data on 5249 individuals in the 1993 Pelotas Birth Cohort Study who were born in Pelotas, Brazil, in 1993. Follow-up data were available for these persons through the ages of 18 and 19 years.

Among the participants, 393 (8.9%) were diagnosed with ADHD at 11 years of age. These patients met diagnostic criteria of the hyperactivity subscale of the Strength and Difficulties Questionnaire, as calibrated for DSM-IV.

Only 60 patients (17.2%), however, continued to have the disorder as young adults.

Additionally, of 492 (12.2%) who met diagnostic criteria for young-adult ADHD, defined according to DSM-V with the exception of age of onset, only 60 (12.6%) had the disorder in childhood.

The findings echo those of an earlier study from New Zealand published in the American Journal of Psychiatry that followed individuals to the age of 38 years. That study showed that as many as 87% of those with adult ADHD did not have prior childhood ADHD; 85% of those with childhood ADHD did not have the disorder in adulthood.

The new study importantly replicates these earlier findings, Dr Rohde told Medscape Medical News.

Dr Rohde added that the findings closely replicate those of the second JAMA study, "giving robustness to the idea that ADHD can be firstly manifested in adults without clear symptomatic routes in childhood," he said.

In the second study, researchers in the United Kingdom and the United States, led by Louise Arseneault, PhD, Medical Research Council Social, Genetic and Psychiatry Centre, Institute of Psychiatry, Psychology, and Neuroscience, London, evaluated a longitudinal sample of 2040 twins born in England and Wales between 1994 and 1995 from the Environmental Risk Longitudinal Twin Study.

The results from this research showed that among 247 individuals who met the DSM-IV criteria for childhood ADHD, 54 (21.9%) met DSM-5 criteria for the disorder at age 18 years.

Factors associated with persistence of ADHD included more symptoms (odds ratio [OR], 1.11) and lower IQ (OR, 0.98).

Of 166 individuals with adult ADHD, more than half (112, 67.5%) did not meet criteria in childhood.

"We identified heterogeneity in the DSM-5 young adult ADHD population such that this group consisted of a large, late-onset ADHD group with no childhood diagnosis, and a smaller group with persistent ADHD," the authors write.

The investigators of the Brazil study note that the 12.2% prevalence of young adult ADHD was significantly higher than the 2.5% to 5% reported in previous studies, including 3.1% reported in the UK study. They explain that the difference likely reflects a lower symptom cutoff required by the DSM-5 and the fact that childhood age at onset was not required to make a diagnosis.

The 8.9% prevalence of childhood ADHD in that study was also higher than the expected rate of about 5.3%; however, that figure is consistent with some previous research, the authors write.

Other factors that were consistent in the Brazil study included higher rates of functional impairment and comorbidities seen in young adult individuals with persistent ADHD.

Those with ADHD had higher rates of criminal behavior, traffic accidents, incarceration, and suicide attempts. The impairments remained after adjusting for co-occurring disorders with ADHD.

"Because comorbidities might be responsible for the aforementioned differences, we ran the same analyses excluding those with co-occurring disorders from the ADHD group and similar results emerged, suggesting that comorbid disorders do not explain the adulthood ADHD impairments," the authors write.

Despite the small percentages of persistence from childhood to adult ADHD, Dr Rohde stopped short of suggesting that ADHD is not a neurodevelopmental disorder, explaining instead that ADHD may in some cases simply have later onset but still be neurodevelopmental, as is the case for schizophrenia.

"Our hypothesis is that some individuals with less severe ADHD symptoms and higher cognitive reserve (higher IQ) living in environments less demanding and/or raised by more supportive families in childhood might present the full syndrome just in adulthood, when demands increase and family support is not developmentally expected," he said.

"This does not mean that these individuals did not have a biological susceptibility for the disorder, but this liability might be lower than the one for those that manifest symptoms earlier," he explained.

"Premature" Conclusions?

In an accompanying editorial, Stephen V. Faraone, PhD, of the Department of Psychiatry and Behavioral Sciences, SUNY Upstate Medical University, Syracuse, New York, and Joseph Biederman, MD, of Massachusetts General Hospital, Boston, note several important limitations that may render the conclusions "premature," including a lack of certainty that the cases of young-adult or adult-onset ADHD were truly new.

"In each study, adult-onset ADHD was de novo only in the sense that full-threshold ADHD had not been diagnosed by the investigators at prior assessments," write the editorialists.

Subthreshold ADHD symptoms, in particular, make the challenge of specifically identifying onset of the disorder murky, they say.

"Our hypotheses about subthreshold ADHD argue against the idea that youth-onset and adult-onset are distinct syndromes," the editorialists write.

Previous research suggests significant underreporting of ADHD symptoms in adults who had the disorder in childhood, as well as overreporting of symptoms among those who did not have ADHD in childhood, they note.

"Because these concerns suggest that the UK, Brazil, and New Zealand studies may have underestimated the persistence of ADHD and overestimated the prevalence of adult-onset ADHD, it would be a mistake for practitioners to assume that most adults referred to them with ADHD symptoms will not have a history of ADHD in youth," the editorialists add.

Mary V. Solanto, PhD, an associate clinical professor in the Department of Psychiatry at the New York University Child Study Center, in New York City, underscored the fact that in earlier versions of the DSM, the inattentive type of ADHD was not included in the criteria for ADHD, meaning that a large portion of children who would today meet the diagnosis for ADHD were not represented in the New Zealand study and the Brazil study.

"We know that there is a sizable percentage of children with the inattentive type of ADHD who would not have been recognized under the earlier criteria, so they would not have been counted as having ADHD, resulting in a lower percentage of children with ADHD," Dr Solanto told Medscape Medical News.

"In my clinical work, I see many adults who come in for evaluation of possible ADHD with problems with attention, organization, and distractibility, and in the vast majority of cases, we do find at least some symptoms of ADHD in childhood, so we need to know more about how clinical samples differ from the epidemiological samples reported in these studies."

The implications of making a misdiagnosis of adult-onset ADHD in cases in which childhood symptoms were not reported could be significant, she added.

"I would be very concerned if practitioners loosely say, 'This is ADHD,' when there aren't childhood symptoms, because patients could have other disorders, including anxiety and depression, which also produce problems of inattention that could be mistaken for ADHD."

Dr Solanto added that the studies nevertheless provide "very interesting and provocative results that need to be pursued.

"The particular advantage of these studies is that they were longitudinal, so that the childhood data were collected at the time, and not dependent on retrospective (and possibly biased) report."

The studies' collective findings should set the stage for more research into ADHD ― perhaps from a new perspective, the editorialists assert.

"For researchers, these new data are a 'call to arms' to study adult-onset ADHD, determine whether and how to incorporate age at onset into future diagnostic criteria, and clarify how it emerges from subthreshold ADHD and other neurodevelopmental anomalies in childhood," they write.

And in clinical practice, the newer evidence should be given some cautious consideration, they add.

"Patients should not be denied services because DSM-5 requires an earlier onset. However, document that the ADHD symptoms are impairing and are not transient effects of another disorder," the editorialists write.

"Be cautious about self-reports of adult-onset ADHD unless convinced that the patients can introspect and have insight into the nature of their problems," they add.

"If you treat children, monitor cases of subthreshold ADHD, especially during times of transition that dismantle environmental scaffolding. In addition, prepare your ADHD patients for the transition to adulthood."

Full disclosures of the authors' and editorialists' financial relationships with industry are available in the published articles. Dr Solanto has disclosed no relevant financial relationships.

JAMA Psychiatry. 2016:73;655-656, 705-712, 713-720. Brazil study abstract, UK/USA study abstract, Editorial

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