Is Posttraumatic Stress Disorder in a Class of Its Own? Longitudinal Comparison to Other Conditions Following Trauma and Life Stress Exposure

Objective: Posttraumatic stress disorder (PTSD) is defined by the assumption that qualifying traumatic events lead to a syndrome distinct from other internalizing disorders, while stressful life events play a prominent role in etiologic theories of major depressive disorder (MDD). We examined whether the environmental etiology of PTSD and MDD are distinct by evaluating the relative contributions of traumatic and stressful life events to both conditions. Harmful alcohol use and physical limitations served as noninternalizing comparators expected to show weaker associations with environmental factors. Methods: Longitudinal cohort study of World Trade Center disaster responders who completed annual assessments of mental health and physical functioning from July 1, 2002, to December 31, 2020. Psychiatric diagnoses were ascertained in clinical interviews. Multivariate regression and multilevel modeling quantified the percentage of variance in psychopathology and physical limitations attributable to trauma versus life stress. Results: 11,153 responders (mean age on September 11, 2001: 37.5 years; 91% male) completed 61,244 visits. The combined environmental effect of 9/11-trauma and life stress on PTSD and MDD was nearly identical (14.3% and 14.8% of between-person variability), but much weaker for alcohol use and physical limitations (0.8% and 9.1%). Life stress explained the most variance in all diagnoses and symptoms across longitudinal and cross-sectional analytic strategies. Conclusions: In the longest study to date coexamining the environmental etiology of PTSD and MDD, trauma and life stress contributed to both conditions. Considering a spectrum of exposures from stressful life events to trauma and integrating knowledge across internalizing conditions may advance understanding and treatment of stress-related psychopathology.