Stress dynamics that maintain posttraumatic stress disorder across 20 years

Abstract

Background: Posttraumatic stress disorder (PTSD) is often chronic and impairing. Mechanisms that maintain symptoms remain poorly understood because of heterogenous presentation. We parsed this heterogeneity by examining how individual differences in stress-symptom dynamics relate to the long-term maintenance of PTSD.

Methods: We studied 7,308 trauma-exposed World Trade Center responders who self-reported PTSD symptoms and stressful life events at annual monitoring visits for up to 20 years (average = 8.8 visits; [range = 4-16]). We used multilevel structural equation models to separate the stable and time-varying components of symptoms and stressors. At the within-person level, we modeled stress reactivity by cross-lagged associations between stress and future symptoms, stress generation by cross-lagged associations between symptoms and future stress, and autoregressive effects represented symptom persistence and stress persistence. The clinical utility of the stress-symptom dynamics was evaluated by associations with PTSD chronicity and mental health care use.

Results: Stress reactivity, stress generation, and symptom persistence were significant on average (bs = 0.03-0.16). There were significant individual differences in the strength of each dynamic (interquartile ranges = 0.06-0.12). Correlations among within-person processes showed some dynamics are intertwined (e.g. more reactive people also generate stress in a vicious cycle) and others represent distinct phenotypes (e.g. people are reactive or have persistent symptoms). Initial trauma severity amplified some dynamics. People in the top deciles of most dynamics had clinically significant symptom levels across the monitoring period and their health care cost 6-17× more per year than people at median levels.

Conclusions: Individual differences in stress-symptom dynamics contribute to the chronicity and clinical burden of PTSD.

Keywords: internalizing psychopathology; life events; life stress; longitudinal; multilevel structural equation model.

Figure 1.

Multi-level structural equation model of stress-symptom dynamics. Note: Stress-symptom dynamics are modeled at the within-person level and individual differences are modeled at the between-person level. Within-person variables reflect deviations in symptoms and stressful events from a person’s average at time t for person i. Between-person latent variables reflect individual differences in the strength of within-person processes and average levels of symptoms/stressors. Single-headed arrows with circles = random slopes. Double-headed arrows = correlations.

Figure 2.

Individual differences in within-person stress-symptom dynamics. Note: Each point is an individual slope estimate. Stress reactivity is the individual’s average cross-lagged stress _t−1 → symptom _t slope; stress generation is the individual’s average cross-lagged symptom _t−1 → stress _t slope; symptom persistence is the individual’s average autoregressive symptom _t−1 → symptom _t slope; stress persistence is the individual’s average autoregressive stress _t−1 → stress _t slope.

Figure 3.

Between-person covariation of stress-symptom dynamics. Note: Each point is an individual slope estimate. The x and y-axes are standardized beta coefficients. Stress reactivity is the individual’s average cross-lagged stress _t−1 → symptom _t slope; stress generation is the individual’s average cross-lagged symptom _t−1 → stress _t slope; symptom persistence is the individual’s average autoregressive symptom _t−1 → symptom _t slope; stress persistence is the individual’s average autoregressive stress _t−1 → stress _t slope.

Figure 4(a).

(a) Mean PCL scores for people at upper and lower deciles of stress-symptom dynamics. Note: Dotted line = threshold for clinically significant symptoms (i.e. PCL total score > 35; Terhakopian et al., 2008). The horizontal line in the box indicates mean level of PCL for that decile. (b) Mental health care expenditures for people at upper and lower deciles of stress-symptom dynamics. Note: Expenditures include cost of mental health care services and psychiatric medications.