Distinguishing sluggish cognitive tempo from attention-deficit/hyperactivity disorder in adults

Researchers who study subtypes of attention-deficit/hyperactivity disorder (ADHD) in children have identified a subset having a sluggish cognitive tempo (SCT) typified by symptoms of daydreaming, mental confusion, sluggish-lethargic behavior, and hypoactivity, among others who differ in many respects from ADHD. No studies have examined the nature and correlates of SCT in adults. This study sought to do so using a general population sample in which those having high levels of SCT symptoms were identified (≥95th percentile) and compared to adults having high levels of ADHD symptoms and adults having both SCT and ADHD symptoms. From a representative sample of 1,249 U.S. adults 18-96 years four groups were created: (a) high levels of SCT but not ADHD (N = 33), (b) high levels of ADHD but not SCT (N = 46), (c) high levels of both SCT and ADHD (N = 39), and (d) the remaining adults as a control group (N = 1,131). As in children, SCT formed a distinct dimension from ADHD symptoms that was unrelated to age, sex, or ethnicity. Adults in both ADHD groups were younger than those with SCT only or control adults. The SCT-only group had less education than the control group, whereas both SCT groups earned less annual income than the control or ADHD-only group. More individuals in the combined group were out of work on disability. In their EF, both SCT groups reported greater difficulties with self-organization and problem solving than controls or the ADHD-only group. Otherwise, the SCT + ADHD group reported significantly greater problems with all other domains of EF than the other groups. But both the SCT-only and ADHD-only groups had significantly more EF difficulties than controls though not differing from each other. A similar pattern was evident on most ratings of psychosocial impairment, except in work and education where SCT was more impairing than ADHD alone and in driving where ADHD was more impairing. SCT contributed unique variance to EF deficits and psychosocial impairment apart from ADHD inattention and hyperactive-impulsive symptoms. Results further suggested that a symptom threshold of 5 or more out of 9 along with a requirement of impairment would result in 5.1% of the population as having SCT. It is concluded that SCT may be a separate disorder from ADHD yet with comorbidity occurring in approximately half of all cases of each.