Traumatic brain injury might be associated with an increased risk of suicide, according to results published Aug. 14 in JAMA.
In a retrospective cohort study of 7,418,391 Danish individuals, including 34,529 who died by suicide, patients with medical contact for traumatic brain injury (TBI) had increased suicide risk, compared with the general population (adjusted incidence rate ratio [IRR] = 1.90; 95% confidence interval, 1.83-1.97).
Patients were aged 10 years or older, and follow-up was conducted from Jan. 1, 1980, until date of death, emigration from Denmark, or Dec. 31, 2014, whichever came first. Data were obtained from national registries, including the Danish Civil Registration System, the Database for Integrated Labour Market Research, the National Hospital Register, the Psychiatric Central Research Register, and the Cause of Death Register. Associations between the separate registries were possible because of unique identification numbers assigned to every resident of Denmark, wrote Trine Madsen, PhD, of the Danish Research Institute of Suicide Prevention at the Mental Health Centre Copenhagen, Capital Region of Denmark, and her coauthors.
TBI was recorded in the National Patient Register and was categorized into three types of injury: mild TBI (concussion), skull fracture without documented TBI, and severe TBI (head injury with evidence of structural brain injury). The number of medical contacts for distinct TBI events, accumulated number of days in hospital treatment, age at first TBI, and time since last medical contact for TBI also were assessed.
Data on psychiatric illness and nonfatal self-harm were obtained from the Psychiatric Central Research Register, because of their association with suicide. Data for deaths by suicide were obtained from the Cause of Death Register. Demographic data collected from other registries included sex, age, marital status, cohabitation status, education, and socioeconomic status. IRRs were calculated using adjusted Poisson regression models.
Of 7,418,391 residents of Denmark included in the follow-up period from 1980 to 2014; 567,823 had a TBI diagnosis. Dr. Madsen and her coauthors also found that 423,502 patients (5.7%) were diagnosed with mild TBI, 24,221 (0.3%) with skull fracture, and 120,100 (1.6%) with severe TBI. A total of 34,529 died by suicide.
Of those who died by suicide, 3,536 (10.2%) had a previous TBI diagnosis (2,701 with mild TBI, 174 with skull fracture, and 661 with severe TBI). The absolute rate of suicide in individuals with hospital contact for TBI was 40.6 per 100,000 person-years (95% CI, 39.2-41.9), compared with 19.9 per 100,000 person-years (95% CI, 19.7-20.1) in those with no hospital contact for TBI.
The fully adjusted analysis showed an IRR of 1.90 (95% CI, 1.83-1.97), as well as an increased risk of suicide by TBI severity. The absolute rate for mild TBI was 38.6 per 100,000 person-years (95% CI, 37.1-40.0) with an IRR of 1.81 (95% CI, 1.74-1.88); 42.4 per 100,000 person-years for skull fracture (95% CI, 36.1-48.7) with an IRR of 2.01 (95% CI, 1.73-2.34, P less than .001), and 50.8 per 100,000 person-years for severe TBI (95% CI, 46.9-54.6) with an IRR of 2.38 (95% CI, 2.20-2.58, P less than .001), compared with individuals with no TBI, the authors wrote.