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In the past, attention deficit hyperactivity disorder (ADHD) was widely considered to affect children and adolescents almost exclusively. �ٺ���Ƶ Health researchers have been instrumental for more than a decade in dispelling that misconception and in identifying the distinct diagnostic markers, neurobiological pathways, behavioral impacts, and comorbidities that characterize adult ADHD.

A Pioneering Researcher

An internationally recognized leader in those efforts is Lenard A. Adler, MD, professor in the Departments of and and director of the Adult ADHD Program at �ٺ���Ƶ. Dr. Adler was among the first researchers to identify key differences in symptom presentation and resulting impairment in adult versus pediatric ADHD—determining, for instance, that physical restlessness tends to be less evident in adults with the disorder, while executive function deficits are often more prominent.

In the early 2000s, Dr. Adler helped develop the World Health Organization ASRS-v1.1 Screener, the first screening tool to evaluate individuals at risk for adult ADHD and still the most widely used (in an updated version, which he co-authored). He was also a principal investigator in the first study of ADHD prevalence in the United States, part of the National Comorbidity Survey, which in 2006 reported that 4.4 percent of U.S. adults had the disorder. That figure, about half the rate observed in children, remains the standard estimate today.

Since then, Dr. Adler has led an array of investigations focused on the neurobiology of adult ADHD and how various types of medication affect it. Because patients often have co-occurring psycho-behavioral conditions, an important facet of his work involves examining how ADHD and other disorders interact.

ADHD versus Sluggish Cognitive Tempo: A Groundbreaking Study

One of Dr. Adler’s ongoing studies seeks to identify the relationship between symptoms of adult ADHD and those of a relatively common but little-understood comorbidity: sluggish cognitive tempo (SCT). First identified in the 1980s, this syndrome does not appear in diagnostic literature such as the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), and debate continues over its proper classification. But in recent years, SCT has gained greater recognition as a condition related to—yet distinct from—the inattentive subtype of ADHD.

“SCT describes people who present as dreamy, spacey, and slow moving,” Dr. Adler explains. “They have difficulty initiating tasks and often seem under-motivated and under-aroused.” In a survey of 1,294 adults with and without ADHD, published in 2012 in the Journal of Abnormal Psychology, researchers found an SCT prevalence rate of 5.8 percent, and half of those meeting the criteria for the syndrome also had ADHD. Other studies have shown that patients with ADHD and with SCT have increased impairment. Such data lead some experts to suggest that SCT’s pathophysiology may differ from that of ADHD, requiring different therapeutic approaches.

The few treatment studies to date of SCT in patients with ADHD lend support to that hypothesis. One trial of methylphenidate in children with ADHD and SCT, for example, found that the response for SCT symptoms was lower than for core ADHD symptoms. A post-hoc analysis of a study of atomoxetine versus placebo in children with ADHD and dyslexia versus dyslexia alone found that controlling for changes in ADHD scores did not significantly influence changes in SCT scores.

Yet no such studies have been completed with adult patients. Dr. Adler and his colleagues—including researchers from �ٺ���Ƶ, the Icahn School of Medicine at Mount Sinai, and SUNY Upstate Medical University—set out to rectify that omission.

Untangling a Complex Interplay of Pathologies

The team designed a two-phase, two-site study of the correlates of SCT in adults with ADHD that will also assess the treatment responsivity of patients with both conditions to the sustained-release stimulant lisdexamfetamine. In October 2019 they published . The paper reported on an analysis of 87 patients with ADHD, examined at �ٺ���Ƶ, to assess how the profiles of those with and without SCT might differ. All participants were men and women ages 18 to 60 who met DSM-5 criteria for a primary diagnosis of inattentive or combined-type ADHD; of these, 48 were also diagnosed with SCT. In addition, both cohorts—SCT-positive and -negative—were tested using rating scales for executive function deficits, emotional dyscontrol, psychiatric comorbidities, and overall impairment.

Participants with a dual diagnosis of ADHD and SCT, the researchers found, had significantly greater clinician-reported inattentive symptoms, clinician-reported emotional dyscontrol, and self-reported executive function deficits, as well as higher overall impairment scores, than those with ADHD alone. “These findings are in line with past research on ADHD and SCT in adults,” notes Dr. Adler. “We did not, however, find differences in hyperactivity-impulsivity in the SCT-positive cohort, unlike some prior studies of adults with ADHD that found a weak but significant association.”

Notably, the team’s findings confirmed earlier research suggesting that SCT affects adults differently from children. “In previous studies, children with ADHD and SCT did not show elevated emotional dyscontrol or executive function deficits compared to those without SCT,” Dr. Adler says. “It may be that when SCT presents or persists into adulthood, it results in deficits in these areas that have not yet developed in children.”

The Importance of Further Research

The second phase of the study, a randomized, placebo-controlled trial of lisdexamfetamine for adults with ADHD and SCT, is currently under review; publication is expected in 2021.

Like all of Dr. Adler’s research on adult ADHD, this investigation serves a broader mission. “Nearly 60 percent of patients diagnosed with ADHD in childhood continue to exhibit symptoms in adulthood, yet only a minority of adult patients are recognized and engaged in treatment,” he says. “Adults with ADHD exhibit significant impairments in interpersonal relationships, academic achievements, and professional attainments. They suffer from high rates of mood and substance use disorders, accidents with injury, and early mortality. It’s critical that we improve our ability to diagnose and manage this disorder at every stage of human development.”