Traumatic stress and risk of severe mental illness: A nationwide cohort study

Introduction A history of traumatic events is prevalent in people with schizophrenia spectrum disorders and mood disorders. However, little is known about their etiological relationship. Objectives To explore whether patients with acute or posttraumatic stress disorder are at higher risk of developing a schizophrenia spectrum disorder or mood disorder. Methods In this prospective cohort study using registers covering the entire Danish population, we used the Danish Psychiatric Central Research Register to identify patients with ICD-10 diagnoses of acute traumatic stress disorder and/or posttraumatic stress disorder. From inpatient and outpatient mental hospitals, we identified 4371 diagnoses with more than 18 million years of follow-up. Main outcomes and measures were relative risks (RR) with 95% confidence intervals (95% CI) of schizophrenia, schizophrenia spectrum disorder, bipolar disorder and mood disorder. Results The incidence of traumatic stress disorder (TSD) has increased steadily from 0.6% in 1996 to 6% in 2012, showed a higher incidence in women and an age distribution with a peak-incidence in early adulthood. We found that diagnoses of TSD increase the risk of schizophrenia (RR 5.85, 95% CI 3.59–8.91), schizophrenia spectrum disorder (RR 3.82, 95% CI 2.38–5.75), bipolar disorder (RR 5.83, 95% CI 3.11–9.83) and mood disorder (RR 4.10, 95% CI 3.15–5.22). Risks were high in the first year after diagnosis of TSD and declined going forward in time. Conclusions Our findings indicate that acute and posttraumatic stress disorder are etiological risk factors for schizophrenia spectrum disorders and mood disorders. If replicated, this may underline treatment of traumatized patients in prevention of severe mental disorder.