Background: Epilepsy and traumatic brain injury are common neurological conditions, with general population prevalence estimates around 0.5% and 0.3%, respectively. Although both illnesses are associated with various adverse outcomes, and expert opinion has suggested increased criminality, links with violent behaviour remain uncertain.
Methods and findings: We combined Swedish population registers from 1973 to 2009, and examined associations of epilepsy (n = 22,947) and traumatic brain injury (n = 22,914) with subsequent violent crime (defined as convictions for homicide, assault, robbery, arson, any sexual offense, or illegal threats or intimidation). Each case was age and gender matched with ten general population controls, and analysed using conditional logistic regression with adjustment for socio-demographic factors. In addition, we compared cases with unaffected siblings. Among the traumatic brain injury cases, 2,011 individuals (8.8%) committed violent crime after diagnosis, which, compared with population controls (n = 229,118), corresponded to a substantially increased risk (adjusted odds ratio [aOR] = 3.3, 95% CI: 3.1-3.5); this risk was attenuated when cases were compared with unaffected siblings (aOR = 2.0, 1.8-2.3). Among individuals with epilepsy, 973 (4.2%) committed a violent offense after diagnosis, corresponding to a significantly increased odds of violent crime compared with 224,006 population controls (aOR = 1.5, 1.4-1.7). However, this association disappeared when individuals with epilepsy were compared with their unaffected siblings (aOR = 1.1, 0.9-1.2). We found heterogeneity in violence risk by age of disease onset, severity, comorbidity with substance abuse, and clinical subgroups. Case ascertainment was restricted to patient registers.
Conclusions: In this longitudinal population-based study, we found that, after adjustment for familial confounding, epilepsy was not associated with increased risk of violent crime, questioning expert opinion that has suggested a causal relationship. In contrast, although there was some attenuation in risk estimates after adjustment for familial factors and substance abuse in individuals with traumatic brain injury, we found a significantly increased risk of violent crime. The implications of these findings will vary for clinical services, the criminal justice system, and patient charities.