Nordstrom A, et al. - This nationwide cohort study was performed to examine whether the risk of dementia decreased over time after traumatic brain injury (TBI). Furthermore, researchers investigated if it was similar for different TBI types and whether it was influenced by familial aggregation. After TBI, the risk of dementia diagnosis decreased over time. However, it was still evident >30 years after the trauma. The association was stronger for more severe TBI and multiple TBIs. Even after adjustment for familial factors, it persisted.

Methods

• The cohort comprised all individuals in Sweden aged ≥50 years on December 31, 2005 (n = 3,329,360).
• The researchers tracked diagnoses of dementia and TBI through nationwide databases from 1,964 until December 31, 2012.
• Individuals diagnosed with TBI (n = 164,334) were matched with up to two controls in a first cohort.
• Subjects diagnosed with dementia during follow-up (n = 136,233) matched with up to two controls were included in second cohort.
• In this study, 46,970 full sibling pairs with discordant TBI status were enrolled the third cohort.

Results

• A total of 21,963 individuals in the first cohort (6.3% with TBI, 3.6% without TBI) were diagnosed with dementia (adjusted odds ratio [OR], 1.81; 95% confidence interval [CI], 1.75-1.86) during a mean follow-up period of 15.3 (range, 0-49) years.
• In the first year after TBI, the association was strongest (OR, 3.52; 95% CI, 3.23–3.84), but the risk remained significant >30 years (OR, 1.25; 95% CI, 1.11–1.41).
• Single mild TBI indicated a weaker association with dementia (OR, 1.63; 95% CI, 1.57–1.70) compared to more severe TBI (OR, 2.06; 95% CI, 1.95–2.19) and multiple TBIs (OR, 2.81; 95% CI, 2.51–3.15).
• In general, these results were confirmed in the nested case-control cohort.
• Furthermore, TBI was correlated with an increased risk of dementia diagnosis in sibling pairs with discordant TBI status (OR, 1.89; 95% CI, 1.62-2.21).
• Therefore, based on the associations found, no causal inferences could be made.