BAL HARBOUR, FLA. – The cognitive impairment seen in some older adults following mild to moderate traumatic brain injury may persist for up to 2 years, according to preliminary results of a longitudinal study.
Previous studies on cognitive impairment following traumatic brain injury (TBI) in older adults have focused on only the first few months of recovery. The current study is one of the few to look at long-term cognitive consequences of TBI in this older population. “Even though the rates of traumatic brain injuries are increasing as our population ages, few studies have examined the cognitive outcomes in this group,” wrote the authors of the poster presented at the annual meeting of the American Neuropsychiatric Association.
The researchers compared 69 older adults hospitalized for TBI with 79 controls matched for age, gender, and education. “Even 2 years after the event, there is evidence of memory, functional, and executive [function] deficits in mild to moderate brain injury patients,” Mark J. Rapoport, M.D., told this newspaper. “We tend to think of these people as better off after a few months.”
“Genetics did not predict outcomes,” said Dr. Rapoport, of Sunnybrook & Women's College Health Sciences Centre, Toronto, Canada.
Previously, researchers found that the presence of the ϵ4 allele in the apolipoprotein E (APOE-ϵ4) gene is associated with increased deposition of amyloid beta-protein after head injury (Nat. Med. 1995;1:135–7). Amyloid beta-protein plays a key role in the pathogenesis of Alzheimer's disease, they noted. Another study supports a negative effect–TBI patients with the APOE-ϵ4 gene had poor cognitive or functional outcome (Neurology 1999;52:244–8).
Both studies suggest a genetic susceptibility to worse outcomes after brain injury. However, a third study found no such effect based on APOE genotype in brain injury patients (Brain 2004;127:2621–8).
“We need to see this over time,” Dr. Rapoport said. The authors noted that APOE genotype might play a more significant role beyond 2 years following an injury, particularly in vulnerable patients (for example, those with mild cognitive impairment).
In the current study, Dr. Rapoport and his colleagues assessed attention, memory, language, and executive function at 1 and 2 years post injury. The investigators controlled for possible confounders, including age, gender, education, APOE genotype, English as a second language, and depression.
The final analysis of data from the first year of the study shows that people with TBI had poorer performance than controls on tests of general cognition, attention/working memory, verbal memory, language, and executive function. There were no differences at 1 year in visual memory test results. A neuropsychiatrist blinded to whether a participant was a case or a control found that no subject met the criteria for Alzheimer's disease or mild cognitive impairment.
The preliminary analysis of the 2-year results suggests there is a greater incidence of impairment in the TBI group versus controls, but the differences between groups are smaller (marginal statistical significance), compared with the first year. Cases had poorer performance than controls on processing speed, verbal memory, language, and word list generation at 2 years. Cases were also rated as having poorer overall functioning than controls.
Possible limitations of the study include recruitment bias and attrition associated with any clinical longitudinal study of TBI. The authors noted that their follow-up rate of more than 70% is higher than rates in similar studies. In addition, investigators did not consider the role of injury severity or psychosocial outcome.
The researchers only enrolled people aged 50 years and older, to be consistent with other studies of TBI in older adults. The average age in the current study was 68 years. Therefore, participants were already at a low baseline risk for mild cognitive impairment or Alzheimer's disease, the authors noted.
“However, subtle changes have developed as early as 2 years post-injury which may be harbingers of more significant and serious cognitive and functional impairment as more time progresses,” they wrote.