Supplementary Material for: Clinical Features of Patients with Alzheimer’s Disease and a History of Traumatic Brain Injury

Introduction: Traumatic brain injury (TBI) has been associated with a greater risk of developing Alzheimer’s disease (AD). Less is known about the clinical features of AD patients with TBI history. The objective of this study was to examine whether a history of TBI and specific injury characteristics are associated with differences in age of disease onset, cognitive features, and neuropsychiatric symptoms (NPSs) in AD patients. Methods: Biomarker-proven AD patients (CSF or amyloid PET) were selected from the Amsterdam Dementia Cohort. TBI events were classified by age at injury (TBI <25 or ≥25 years) and TBI severity (loss of consciousness, multiple events). Cognitive composite scores were calculated from results of a neuropsychological test battery. NPSs were assessed with the Neuropsychiatric Inventory Questionnaire (NPI-Q). Linear regression analyses were utilized to examine associations between TBI, TBI characteristics, and clinical outcome measures. Results: Among the 1,755 selected AD patients (mean age = 65.2 years), 166 (9.5%) had documented ≥1 TBI in their medical history. Overall, TBI history was not related to differences in age of disease onset, but age at injury <25 years old was associated with 2.3 years earlier age at symptom onset (B = −2.34, p = 0.031). No significant associations were found between TBI history or TBI characteristics and differences in cognition or NPSs. Conclusion: Our results underscore previous findings on the vulnerability of the brain during critical maturation phases and suggest that an early TBI may contribute to lower resilience to neurodegenerative changes.