Psychiatric illness after traumatic brain injury (TBI) has been shown
to be prevalent in hospitalized and tertiary care patient populations.
To determine the risk of psychiatric illness after TBI in an adult health
maintenance organization population.
Prospective cohort study.
Large staff-model health maintenance organization.
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.
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.
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