The role of arousal symptoms in PTSD and depression comorbidity: a longitudinal network analysis among adolescents after a natural disaster

Background: Posttraumatic stress disorder (PTSD) and depression frequently co-occur in adolescents following trauma, but the symptom-level mechanisms underlying this comorbidity remain unclear. The arousal symptoms of PTSD, including sleep problems and other symptoms, are a potential bridging symptom group. This study aimed to investigate the dynamic bridge symptoms linking PTSD and depression among adolescents exposed to a natural disaster, and to examine how these connections evolve over time. Methods: A longitudinal study was conducted with 1,444 adolescents affected by the Zhouqu debris flow. Participants were assessed at 3, 15, and 27 months post-disaster. The University of California at Los Angeles Posttraumatic Stress Reaction Index for Children, revision 1 and the Child Depression Inventory were used to assess PTSD and depression symptoms, respectively. Two cross-lagged panel network (CLPN) models were used to estimate temporal symptom associations and to identify bridge symptoms based on bridge expected influence (BEI). Results: Symptoms in the arousal and reactivity cluster (e.g. sleep disturbance, startle response, concentration problems) exhibited high and stable BEI across two years. However, specific bridge symptoms shifted across phases: startle and irritability were more influential between 3 and 15 months, while concentration problems and anhedonia became more prominent between 15 and 27 months. Network comparison revealed limited structural overlap across time, highlighting stage-specific changes in comorbidity patterns. Conclusions: These findings support a dual-phase mechanism of comorbidity between PTSD and depression. Arousal-related symptoms primarily drive cross-disorder associations in the early stage (3–15 months). In the later stage (15–27 months), depressive symptoms, especially anhedonia, become central, with attentional problems from hyperarousal also contributing. Tailored interventions targeting distinct symptom profiles at different recovery stages (hyperarousal in 3–15 month and anhedonia in 15–27 months) may enhance the effectiveness of post-disaster mental health care.