Progression of externalizing disorders into anxiety disorders: Longitudinal transitions in the first three decades of life.

Background: There is a notable comorbidity between externalizing disorders and anxiety disorders, which may be explained by the co-occurrence of two prevalent early-onset disorders, by shared vulnerability and risk factors, or as evidence that one disorder group might be causally related to the other.

Aim: To investigate the longitudinal trajectories of externalizing disorders, their interplay with anxiety disorders, and putative predictors for symptom progression in youth.

Methods: 1053 adolescents (14-17 years) from the general population were assessed at baseline and prospectively at 2, 4, and 10-year follow-up using a standardized interview of mental disorders (DIA-X/M-CIDI) to assess "early" (oppositional-defiant disorder, conduct disorder, ADHD) and "late" (antisocial behavior, substance use disorders) externalizing disorders as well as anxiety disorders. Longitudinal associations and predictors for symptom progression were examined using Kaplan-Meier-analyses.

Results: Lifetime prevalence of early externalizing disorders were 9.1% and 6.4% among those with and without any anxiety disorder. A late externalizing disorder was reported by 50.3% of those with an early externalizing disorder and in 26.6% of those with any anxiety disorder. Both early (HR: 1.5, 95%CI: 1.0-2.3) and late externalizing disorders (HR: 2.1, 95%CI: 1.7-2.6) were associated with incident anxiety disorders. Higher parental rejection, lower volitional inhibition, and higher volitional avoidance predicted incident anxiety disorders among those with early externalizing disorders.

Discussion: Early externalizing disorders likely follow a homotypic continuity (to late externalizing disorders) and/or a heterotypic continuity to anxiety disorders, and thus appear as a useful target for prevention and early intervention.