Psychiatric illness following traumatic brain injury in an adult health maintenance organization population

Background: Psychiatric illness after traumatic brain injury (TBI) has been shown to be prevalent in hospitalized and tertiary care patient populations. Objective: To determine the risk of psychiatric illness after TBI in an adult health maintenance organization population. Design: Prospective cohort study. Setting: Large staff-model health maintenance organization. Participants: Nine hundred thirty-nine health plan members diagnosed as having TBI in 1993 and enrolled in the prior year, during which no TBI was ascertained. Three health plan members per TBI-exposed subject were randomly selected as unexposed comparisons, matched for age, sex, and reference date. Main Outcome Measure: Psychiatric illness in the 3 years after the TBI reference date, determined using computerized records of psychiatric diagnoses according to the International Classification of Diseases, Ninth Revision, Clinical Modification, prescriptions, and service utilization. Results: Prevalence of any psychiatric illness in the first year was 49% following moderate to severe TBI, 34% following mild TBI, and 18% in the comparison group. Among subjects without psychiatric illness in the prior year, the adjusted relative risk for any psychiatric illness in the 6 months following moderate to severe TBI was 4.0 (95% confidence interval [CI], 2.4-6.8) and following mild TBI was 2.8 (95% CI, 2.1-3.7; P<.001) compared with those without TBI. Among subjects with prior psychiatric illness, the adjusted relative risk for any psychiatric illness in the 6 months following moderate to severe TBI was 2.1 (95% CI, 1.3-3.3) and following mild TBI was 1.6 (95% CI, 1.2-2.0; P = .005). Prior psychiatric illness significantly modified the relationship between TBI and subsequent psychiatric illness (P = .04) and was a significant predictor (P<.001). Persons with mild TBI and prior psychiatric illness had evidence of persisting psychiatric illness. Conclusions: Both moderate to severe and mild TBI are associated with an increased risk of subsequent psychiatric illness. Whereas moderate to severe TBI is associated with a higher initial risk, mild TBI may be associated with persistent psychiatric illness.