By BENEDICT CAREY
In just the past few years, researchers have identified what they believe is an adult version of attention deficit disorder: a restless inability to concentrate that develops spontaneously after high school, years after the syndrome typically shows itself, and without any early signs.
The proposed diagnosis — called adult-onset A.D.H.D. and potentially applicable to millions of people in their late teenage years or older — is distinct from the usual adult variety, in which symptoms linger from childhood.
Yet a new study suggests that adult-onset A.D.H.D. is rare — if it exists at all.
The paper, published Friday in the American Journal of Psychiatry, could deepen the debate over these symptoms rather than settle it. Previously, three large analyses had estimated the prevalence of the disorder at 3 to 10 percent of adults.
The new study, while smaller, mined more extensive medical histories than earlier work and found that most apparent cases of adult-onset attention deficits are likely the result of substance abuse or mood problems.
“This study carefully considered whether each person met criteria for A.D.H.D. and also fully considered other disorders” that might better explain the symptoms, said Mary Solanto, an associate professor of pediatrics at the Zucker School of Medicine at Hofstra/Northwell. “In all those respects, it is the most thorough study we have looking at this issue.”
Dr. Solanto said the study all but ruled out adult-onset A.D.H.D. as a stand-alone diagnosis. Other experts cautioned that it was too early to say definitively, and noted that attention deficits often precede mood and substance abuse problems — which in turn can mask the condition.
The new analysis drew on data from a study of childhood A.D.H.D. that had tracked people from age 9 or 10 up through early adulthood, gathering detailed histories from multiple sources, including doctors and parents.
That project, begun in 1994, recruited 579 children with diagnosed A.D.H.D., as well as a group of 289 in the same classrooms for comparison purposes.
Of those “control” youngsters, the new study found, 24 would go on to develop attention deficit problems much later on, during high school or after. Classic A.D.H.D. is diagnosed between ages 5 and 12.
The authors of the new report, led by Margaret Sibley, an associate professor of psychiatry and behavioral health at Florida International University, carefully examined the extensive records of those 24 with adult-onset A.D.H.D. The researchers found that the attention deficits in all but five cases most likely stemmed from other causes, like marijuana use, depression or anxiety.
And the remaining five were hardly straightforward cases: One subject had previously had an eating disorder, another had shown signs of mania.
“This suggests to me the diagnosis doesn’t exist independent of a compelling psychiatric history,” said Dr. Sibley. “No one in our group developed A.D.H.D. in adulthood out of nowhere.”
Some 10 percent of children are given a diagnosis of A.D.H.D., and most grow out of it to some extent. One reason that symptoms may emerge seemingly from nowhere in high school or later, experts say, is that some youngsters have offsetting abilities, like high I.Q., or supports, such as sensitive parents or teachers, that mask the problems early on.
In this respect, upbringing and environment may effectively blunt or contain symptoms.
Not all experts believe the new report is the last word.
“When we take out all those people who have complicating problems, like substance use and mood disorders, we still find that about a third of late-onset cases remain,” said Jessica Agnew-Blais, a postdoctoral research fellow at the Institute of Psychiatry, Psychology and Neuroscience at King’s College London.
She was co-author of a previous study that estimated the prevalence of adult-onset A.D.H.D. at about 6 percent. “What this discrepancy points to is that it’s important to look at different populations,” Dr. Agnew-Blais said of the new findings.
“I don’t think clinicians should be shutting the door, if the only sticking point is the age of onset of symptoms,” she added.