Relations Among Suicidal Ideation, Depressive Symptoms, and Functional Independence During the 10 Years After Traumatic Brain Injury: A Model Systems Study.

OBJECTIVE: To investigate relative causality in relations among suicidal ideation (SI), depressive symptoms, and functional independence over the first 10 years after traumatic brain injury (TBI). DESIGN: Prospective longitudinal design with data collected through the Traumatic Brain Injury Model Systems (TBIMS) network at acute rehabilitation hospitalization as well as 1, 2, 5, and 10 years after injury. SETTING: United States Level I/II trauma centers and inpatient rehabilitation centers with telephone follow-up. PARTICIPANTS: Individuals enrolled into the TBIMS National Database (N=9539) with at least 1 SI score at any follow-up data collection (72.1% male; mean age, 39.39y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Patient Health Questionnaire-9 and FIM at years 1, 2, 5, and 10 post injury. RESULTS: A cross-lagged panel structural equation model, which is meant to indirectly infer causality through longitudinal correlational data, suggested that SI, depressive symptoms, and functional independence each significantly predicted themselves over time. Within the model, bivariate correlations among variables were all significant within each time point. Between years 1 and 2 and between years 2 and 5, depressive symptoms had a larger effect on SI than SI had on depressive symptoms. Between years 5 and 10, there was reciprocal causality between the 2 variables. Functional independence more strongly predicted depressive symptoms than the reverse between years 1 and 2 as well as years 2 and 5, but its unique effects on SI over time were extremely marginal or absent after controlling for depressive symptoms. CONCLUSIONS: A primary goal for rehabilitation and mental health providers should be to monitor and address elevated symptoms of depression as quickly as possible before they translate into SI, particularly for individuals with TBI who have reduced functional independence. Doing so may be a key to breaking the connection between low functional independence and SI.