Attention-Deficit/Hyperactivity Disorder Symptoms and Externalizing Progression in the LAMS Study: A Test of Trait Impulsivity Theory.

Objective To test differential prospective prediction of growth in externalizing behavior, including oppositional defiant disorder, conduct disorder, and substance use disorders, by earlier hyperactive-impulsive (HI) vs inattentive (IN) symptoms of attention-deficit/hyperactivity disorder (ADHD). Method Participants in the Longitudinal Assessment of Manic Symptoms (LAMS) Study (N = 685 at study entry), including 458 boys and 227 girls ages 6–12, completed full parent report and self-report assessments every year for 8 years on the Schedule for Affective Disorders and Schizophrenia for School-Age Children. Three sets of analyses were conducted. First, hierarchal regression (block entry) was used to test independent associations between HI symptoms and later externalizing outcomes, controlling for IN symptoms, and IN symptoms and later externalizing outcomes, controlling for HI symptoms. Second, logistic regression was used to test progression of DSM externalizing disorders. Third, tests of mediation were used to assess potentiation of externalizing progression through environmental risk mediators (eg, family environment, neighborhood violence). Results Consistent with hypotheses derived from trait impulsivity theories of externalizing behavior, HI symptoms of ADHD were associated independently with long-term externalizing outcomes, whereas IN symptoms were not. Between months 48 and 96, ADHD-HI/combined symptom subtype diagnoses predicted later oppositional defiant disorder diagnoses, oppositional defiant disorder diagnoses predicted later conduct disorder diagnoses, and conduct disorder diagnoses predicted later substance use disorder diagnoses. Evidence for environmental risk mediation (eg, parental monitoring, neighborhood violence) was also found. Conclusion Findings support trait impulsivity models of externalizing progression, whereby ADHD-HI/combined symptoms subtypes predispose to increasingly severe externalizing behaviors, which are magnified in contexts of environmental risk.