Associations between posttraumatic stress and comorbidities of traumatic brain injury and substance use disorders with Alzheimer's disease in older veterans: A narrative review

Posttraumatic stress disorder (PTSD) exhibits high rates of comorbidity with Substance Use Disorders (SUDs) and Traumatic Brain Injury (TBI), especially in older adults who are subject to the effects of psychological trauma due to combat exposure, health-related and psychosocial outcomes, and aging. This narrative review explores the associations between PTSD and comorbidities of psychoactive substance abuse and traumatic brain injuries on the incidence of Alzheimer's disease (AD) in veterans aged 55 > , according to existing literature. The account of genetic predisposition in reference to the presence of the Apolipoprotein e4 gene was also considered. Biomarkers of AD, including beta-amyloid and phosphorylated tau levels in cerebrospinal fluids (CSF), were analyzed in PTSD, TBI and SUD conditions. This review was conducted as a narrative summary utilizing three separate search engines. Inclusion of data was primarily determined by a single reviewer with a randomized 10 % of 49 selected studies cross screened by a second reviewer. Two additional independent reviewers incrementally cross-checked the 49 included studies at full-text stages for accuracy and consistency. The literature review found that PTSD and comorbidities of TBI and SUD may share increased incidence of AD and related dementia, however, a causal relationship cannot be implied. Conflicting results on CSF biomarker trends for each comorbidity and complications arising from genetic predispositions indicate a need for future studies to clarify the relationship between PTSD comorbidities on the onset of AD. Expanded biomarker analysis has not yet been assessed. Implications of this review may lead to alternative treatment and care methods for older adults/veterans suffering from psychological impairment to prevent the formation of comorbidities and lower existing elevated risks for AD onset and progression.