The data suggest that traumatic brain injury (TBI) in older veterans may predispose them toward development of symptomatic dementia. And they raise concern about the potential long-term consequences of TBI in younger veterans.
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The data suggest that TBI in older veterans may predispose them toward development of symptomatic dementia.
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Increased Dementia Risk in Older Veterans with Brain Injury
The relationship between traumatic brain injury (TBI) and risk of dementia remains unclear, with some studies suggesting an increased risk and others finding no association.
Kristine Yaffe, MD, Professor of Psychiatry, Neurology and Epidemiology at the University of California, San Francisco (UCSF) and Director of the Memory Disorders Program at the San Francisco VA Medical center, and colleagues believe that it is particularly important to clarify the association between TBI and dementia given the large number of soldiers experiencing TBI as part of current conflicts.
The researchers reviewed medical records of 281,540 U.S. veterans age 55 years and older who received care through the Veterans Health Administration and had at least one inpatient or outpatient visit during 1997-2000 and a follow-up during 2001-2007, and who did not have a dementia diagnosis at the start of the study.
They searched the database for TBI and dementia diagnoses and investigated whether TBI of any type was associated with greater risk of dementia, while taking into account demographics and other medical conditions, including psychiatric disorders.
The risk of dementia was 15.3% in those with a TBI diagnosis compared with 6.8% in those without a TBI diagnosis (p< 0.001).
The adjusted hazard ratio for incident dementia in those with any TBI diagnosis was 2.3 (95% confidence interval: 2.1, 2.5) – a more than two-fold increase in the risk of developing dementia over seven years – and was significant for all TBI types. Approximately two percent of older veterans had a TBI diagnosis during the study period.
"This issue is important because TBI is very common," said Yaffe. "About 1.7 million people experience a TBI each year in the United States, primarily due to falls and car crashes. TBI is also referred to as the 'signature wound' of the conflicts in Iraq and Afghanistan, where TBI accounts for 22 percent of casualties overall and 59 percent of blast-related injuries."
The data suggest that TBI in older veterans may predispose them toward development of symptomatic dementia. And they raise concern about the potential long-term consequences of TBI in younger veterans," Yaffe said.
The researchers suggest that there are several potential mechanisms by which TBI could increase dementia risk. TBI is associated with swelling of axons, the long cell extensions that form connections among nerve cells in the brain. This swelling is accompanied by accumulation of proteins, including beta-amyloid, which is a hallmark of Alzheimer's disease.
In fact, according to the researchers, amyloid plaques similar to those found in the brains of people with Alzheimer's are present in up to 30 percent of TBI patients who do not survive their injuries, regardless of age.
It is possible that these injuries result in the death of axons and neurons, even after a single TBI. Loss of axons and neurons could result in earlier manifestation of Alzheimer's symptoms. "Our findings raise hope that early treatment and rehabilitation following TBI may help prevent long-term consequences such as dementia," Yaffe said. "They also suggest that older adults who experience a TBI should be monitored for signs of cognitive impairment following their injuries."
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Original content Bob DeMarco, the Alzheimer's Reading Room