Traumatic Stress Disorders and Risk of Subsequent Schizophrenia Spectrum Disorder or Bipolar Disorder: A Nationwide Cohort Study

Objective: Traumatic stress disorders are prevalent in patients with schizophrenia and bipolar disorder. However, there is a lack of prospective longitudinal studies investigating the risk of severe mental illness for people diagnosed with traumatic stress disorders. We aimed to assess if patients with acute stress reaction (ASR) or post-traumatic stress disorder (PTSD) are at increased risk of schizophrenia spectrum disorders or bipolar disorder. Methods: We performed a prospective cohort study covering the entire Danish population including information on inpatient and outpatient mental hospitals over 2 decades. Predictors were in-or outpatient diagnoses of ASR or PTSD. We calculated incidence rate ratios (IRR) with 95% CIs of schizophrenia, schizophrenia spectrum disorder, and bipolar disorder. Results: Persons with a traumatic stress disorder had a significantly increased risk of schizophrenia (IRR 3.80, CI 2.33-5.80), schizophrenia spectrum disorder (IRR 2.34, CI 1.46-3.53), and bipolar disorder (IRR 4.22, CI 2.25-7.13). Risks were highest in the first year after diagnosis of the traumatic stress disorder and remained significantly elevated after more than 5 years. Mental illness in a parent could not explain the association. Conclusion: Our findings support an association between diagnosed traumatic stress disorders and subsequent schizophrenia spectrum disorder or bipolar disorder. If replicated, this may increase clinical focus on patients with traumatic stress disorders.