Absolute risk of acquired brain injury and rehabilitation needs in Denmark, 2014–2023: a population-based prospective cohort study

Background: Although frequency estimates for many types of acquired brain injuries are available, absolute risk estimates (percentage of individuals who develop the disease during their lifetime) remain sparse. We aimed to create comprehensive, absolute risk estimates of acquired brain injury and rehabilitation needs. Methods: In this prospective cohort study, we followed all individuals residing in Denmark from January 1, 2014, to December 31, 2023. We used population-based registers covering the entire Danish population (N = 5.7 million). People with acquired brain injury were identified through the Danish National Patient Register, including stroke, traumatic brain injury, encephalopathy, brain infection, and brain tumour. We estimated lifetime risks, absolute risks, and incidence rates for each acquired brain injury. We estimated one-year prevalence of acquired brain injury, rehabilitation need, and mortality. Estimates were stratified by age and sex. Findings: The lifetime risk of acquired brain injury was 35.62% (95% confidence interval [CI], 35.50-35.73). The incidence rate of acquired brain injury was 48.11 per 10,000 person-years (95% CI, 47.91-48.30). Stroke had the highest lifetime risk of 19.62% (95% CI, 19.52-19.72), while brain infections had lowest lifetime risk of 1.43% (95% CI, 1.41-1.46). The one-year prevalence of rehabilitation need among patients with acquired brain injury was 28.18% (95% CI, 27.73-28.63). The prevalence varied across diagnostic groups and ages; it was highest in older patients and in patients with stroke (43.22%) and lowest in patients with traumatic brain injury (10.03%). Interpretation: One in three individuals will experience an acquired brain injury during their lifetime, underscoring the substantial public health burden. Rehabilitation needs varied markedly by diagnosis and age, indicating genuinely different needs across diagnostic groups, but also highlights the need for further research to determine whether differences reflect unassessed needs. Funding: Health Research Foundation of Central Denmark Region.