Differential associations between traumatic brain injury severity and four dementia phenotypes in military veterans

National Veterans Affairs electronic health records were used to examine the association between traumatic brain injury (TBI) severity and four dementia phenotypes ranging from narrow (strict AD) to broad (all-cause dementia).

Veterans with TBI (n = 91,753) and a propensity score-matched comparison group of veterans without TBI (n = 183,506) were included. Four validated dementia phenotypes defined using International Classification of Diseases (ICD) codes were evaluated. The association between TBI severity and each dementia phenotype was examined using adjusted logistic regression.

TBI severity was significantly associated with increased odds of developing dementia across the three broader dementia phenotypes in a dose-response manner (moderate/severe/penetrating TBI > mild TBI). Those with unclassified TBI had disease risk falling in between mild and more severe TBI. In contrast, TBI was associated with decreased risk of strict AD across all severity levels.

Findings support a dose-response relationship between TBI severity and broader dementia risk but raise questions regarding the TBI-AD link.