Longitudinal trajectories of comorbid PTSD and depression symptoms among US service members and veterans

Background: Posttraumatic stress disorder (PTSD) often co-occurs with other psychiatric disorders, particularly major depressive disorder (MDD). The current study examined longitudinal trajectories of PTSD and MDD symptoms among service members and veterans with comorbid PTSD/MDD. Methods: Eligible participants (n = 1704) for the Millennium Cohort Study included those who screened positive at baseline for both PTSD (PTSD Checklist-Civilian Version) and MDD (Patient Health Questionnaire). Between 2001 and 2016, participants completed a baseline assessment and up to 4 follow-up assessments approximately every 3 years. Mixture modeling simultaneously determined trajectories of comorbid PTSD and MDD symptoms. Multinomial regression determined factors associated with latent class membership. Results: Four distinct classes (chronic, relapse, gradual recovery, and rapid recovery) described symptom trajectories of PTSD/MDD. Membership in the chronic class was associated with older age, service branch, deployment with combat, anxiety, physical assault, disabling injury/illness, bodily pain, high levels of somatic symptoms, and less social support. Conclusions: Comorbid PTSD/MDD symptoms tend to move in tandem, and, although the largest class remitted symptoms, almost 25% of participants reported chronic comorbid symptoms across all time points. Results highlight the need to assess comorbid conditions in the context of PTSD. Future research should further evaluate the chronicity of comorbid symptoms over time.