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.