The Presence of Externalizing Diagnoses Increases the Risk of Suicidal Thoughts and Behaviors in Youth Enriched for Early-Onset Depression

Objective: To understand the additional impact of externalizing diagnoses and specific externalizing symptoms (eg, impulsivity, irritability) on risk for suicidal thoughts and behaviors (STBs) in a sample of youth enriched for depression. Method: Participants included 219 children from the Pediatric Suicidality Study, which has followed a sample of preschoolers enriched for depression into early adolescence (ages 10-14 years). Semistructured interviews to assess STBs and clinical diagnoses including major depressive disorder (MDD), attention-deficit/hyperactivity disorder (ADHD), and oppositional defiant disorder (ODD) were conducted at preschool age (3-6 years), preadolescence (8-12 years), and 2 years later (10-14 years). Results: Meeting diagnostic criteria for an externalizing disorder at any study time point was significantly associated with experiencing STBs after the preschool period, even when controlling for comorbid depression (66.7% vs 27.6%; χ² = 5.70, p = .017). Findings were similar when limiting the analyses to suicidal behaviors only (77.3% vs 44.6%; χ² = 4.00, p = .045). Analyses examining specific externalizing symptoms found that impulsivity and irritability, but not inattention or defiance, were significantly associated with experiencing STBs across the 2 years between follow-up visits leading into early adolescence (impulsivity: estimate = 0.68, SE = 0.29, χ² = 5.47, p = .019; irritability: estimate = 0.94, SE = 0.35, χ² = 7.39, p = .007). Conclusion: Youth with comorbid depression and an externalizing disorder or externalizing symptoms of irritability or impulsivity may be at an elevated risk of STBs into early adolescence. These findings highlight the importance of early identification and treatment of externalizing disorders and symptoms in addition to treating depression when managing STBs in this population and provide additional potential treatment targets. Plain language summary: A sample of preschoolers enriched for depression was followed into early adolescence and assessed for suicidal thoughts and behaviors (STBs), major depressive disorder (MDD), attention-deficit/hyperactivity disorder (ADHD), and oppositional defiant disorder (ODD). Having an externalizing disorder (eg, ADHD or ODD) at any time was significantly associated with STBs after the preschool period. Further, externalizing symptoms of impulsivity and irritability, but not inattention or defiance, were significantly associated with STBs across the two years between follow-up visits leading into early adolescence. These findings highlight the importance of identifying and treating externalizing disorders and symptoms in addition to treating depression when managing STBs in this population.