Traumatic brain injury (TBI) is a leading cause of death and disability in individuals over 45 years of age in industrialized countries. Single and repeated TBI is linked to progressive neurodegeneration and has been identified as a risk factor for dementia and Alzheimer’s disease, which accounts for roughly 60 to 80% of dementia cases. Characterized by progressive memory loss and cognitive decline, Alzheimer’s disease and other dementias are responsible for profound functional consequences in adults and typically are fatal. While most individuals develop Alzheimer’s disease after age 65, a smaller subset of the population will experience early-onset Alzheimer’s disease.
Alzheimer’s disease itself is an underlying risk factor for TBI, as people suffering with dementia are more prone to falls and other injuries. In many cases, a dementia diagnosis may not occur until a person seeks medical care for TBI. One study observing 21,276 individuals with and without dementia and TBI found that the risk of being diagnosed with dementia in the first year after TBI was four to six times higher than individuals with dementia who did not have a TBI. The study also found that the risk of dementia diagnosis increased by 80% for individuals diagnosed with TBI in a 15-year follow up period, compared to those without TBI.
While extensive research has affirmed the link between TBI and Alzheimer’s disease, no previous studies have identified specific clinical differences in dementia symptoms of patients with and without TBI history. A team of researchers investigated these gaps in clinical knowledge by conducting a study on 1,755 patients with Alzheimer’s disease. The researchers found no significant associations between TBI history and cognitive features during the disease. However, it was found that individuals who experienced TBI under the age of 25 experienced Alzheimer’s disease symptom onset an average of 2.3 years earlier than those with TBI over age 25 years.
This study’s findings suggest that TBI is a risk factor for Alzheimer’s disease, but it does not alter the clinical features of the disease once it is present. Individuals with a history of TBI should be screened by clinicians for symptoms of Alzheimer’s disease and other dementias, especially at earlier ages than the general population.
When is the risk for dementia highest?
- Earlier age at TBI. The finding that TBI occurring before age 25 was associated with younger diagnosis of Alzheimer’s disease suggests that clinicians, families, and caretakers should closely monitor the status of individuals continually in the years following TBI. Another study found that TBI was most significantly associated with dementia diagnosis in individuals younger than age 65 than those diagnosed at 65 years or older. Overall, the age of both the injury and the diagnosis of neurodegenerative disease are important factors in the association between TBI and Alzheimer’s disease.
- Multiple TBIs. The likelihood of developing dementia was significantly associated with a history of multiple TBIs. Experiencing a TBI is a risk factor for consequent TBIs, so individuals with TBI must be vigilant in the prevention of future injuries in order to reduce their risk for developing dementia.
- Severe TBI. Overall, a single mild TBI demonstrates the weakest association with a dementia diagnosis, indicating that the severity of injury plays a role in dementia development.
What are the clinical features of Alzheimer’s disease?
- While the most recent study found no specific clinical features for Alzheimer’s disease preceded by TBI, it is still important to look out for these Alzheimer’s symptoms in individuals who have experienced TBI:
- Cognition. The cognitive symptoms of Alzheimer’s disease are broad and can vary from person to person, but certain signs are strong indicators. Linguistic fluency, attention, and memory may all be impacted by the development of the disease, so changes in these abilities may be indicative of a problem.
- Neuropsychiatric symptoms. In addition to cognitive deficits, individuals with Alzheimer’s disease may experience neuropsychiatric dysfunction in the form of delusions, aggression, depression, and anxiety. Moreover, these behaviors may be accompanied by changes in appetite, night-time behavior, and hallucinations.
References:
Amerongena S, Catona D, Pijnenburga Y, et al. Clinical features of patients with Alzheimer’s disease and a history of traumatic brain injury. Dementia and Geriatric Cognitive Disorders Extra. (September 2022).
Barnes D, Byers A, Gardner R, et al. Association of mild traumatic brain injury with and without loss of consciousness with dementia in US military veterans. JAMA Neurology. (September 2018).
Nordstrom A, Nordstrom P. Traumatic brain injury and the risk of dementia diagnosis: A nationwide cohort study. PLOS Medicine. (January 2018).