(Boston) -- Although much research has examined traumatic brain injury (TBI) as a possible risk factor for later life dementia from neurodegenerative diseases such as Alzheimer's disease (AD), little is known regarding how TBI influences the rate of age-related cognitive change. A new study now shows that history of TBI (with loss of consciousness) does not appear to affect the rate of cognitive change over time for participants with normal cognition or even those with AD dementia.
These findings appear in the Journal of Alzheimer's Disease.
More than 10 million individuals worldwide are affected annually by TBI, however the true prevalence is likely even greater given that a majority of TBIs are mild in severity and may not be recognized or reported. TBI is a major public health and socioeconomic concern resulting in $11.5 billion in direct medical costs and $64.8 billion in indirect costs to the U.S. health system in 2010 alone.
According to the researchers the relationship between TBI and long-term cognitive trajectories remains poorly understood due to limitations of previous studies, including small sample sizes, short follow-up periods, biased samples, high attrition rates, limited or no reports of exposure to repetitive head impacts (such as those received through contact sports), and very brief cognitive test batteries.
In an effort to examine this possible connection, researchers compared performance on cognitive tests over time for 706 participants (432 with normal cognition; 274 AD dementia) from the National Alzheimer's Coordinating Center database. Normal and AD dementia participants with a history of TBI with loss of consciousness were matched to an equal number of demographically and clinically similar participants without a TBI history. The researchers also examined the possible role of genetics in the relationship between TBI and cognitive decline by studying a gene known to increase risk for AD dementia, the APOE ε4 gene.
"Although we expected the rates of cognitive change to differ significantly between those with a history of TBI compared to those with no history of TBI, we found no significant difference between the groups, regardless of their APOE genotype," explained corresponding author Robert Stern, PhD, Director of the Clinical Core of the Boston University Alzheimer's Disease Center (BU ADC) and professor of neurology, neurosurgery and anatomy and neurobiology at Boston University School of Medicine.
The study's first author Yorghos Tripodis, PhD, Associate Director of the Data Management and Biostatistics Core of the BU ADC and associate professor of Biostatistics at Boston University School of Public Health, cautioned, "Our findings should still be interpreted cautiously due to the crude and limited assessment of TBI history available through the NACC database." The researchers recommended that future studies should collect information on the number of past TBIs (including mild TBIs, as well as exposure to sub-concussive trauma through contact sports and other activities) along with time since TBI, which may play a significant role in cognitive change.
The study is funded by NIA/NIH grant P30 AG013846 (PI Neil Kowall, MD). The NACC database is funded by NIA/NIH Grant U01 AG016976. NACC data are contributed by the NIA funded ADCs: P30 AG019610 (PI Eric Reiman, MD), P30 AG013846 (PI Neil Kowall, MD), P50 AG008702 (PI Scott Small, MD), P50 AG025688 (PI Allan Levey, MD, PhD), P50 AG047266 (PI Todd Golde, MD, PhD), P30 AG010133 (PI Andrew Saykin, PsyD), P50 AG005146 (PI Marilyn Albert, PhD), P50 AG005134 (PI Bradley Hyman, MD, PhD), P50 AG016574 (PI Ronald Petersen, MD, PhD), P50 AG005138 (PI Mary Sano, PhD), P30 AG008051 (PI Steven Ferris, PhD), P30 AG013854 (PI M. Marsel Mesulam, MD), P30 AG008017 (PI Jeffrey Kaye, MD), P30 AG010161 (PI David Bennett, MD), P50 AG047366 (PI Victor Henderson, MD, MS), P30 AG010129 (PI Charles DeCarli, MD), P50 AG016573 (PI Frank LaFerla, PhD), P50 AG016570 (PI Marie-Francoise Chesselet, MD, PhD), P50 AG005131 (PI Douglas Galasko, MD), P50 AG023501 (PI Bruce Miller, MD), P30 AG035982 (PI Russell Swerdlow, MD), P30 AG028383 (PI Linda VanEldik, PhD), P30 AG010124 (PI John Trojanowski, MD, PhD), P50 AG005133 (PI Oscar Lopez, MD), P50 AG005142 (PI Helena Chui, MD), P30 AG012300 (PI Roger Rosenberg, MD), P50 AG005136 (PI Thomas Montine, MD, PhD), P50 AG033514 (PI Sanjay Asthana, MD, FRCP), P50 AG005681 (PI John Morris, MD), and P50 AG047270 (PI Stephen Strittmatter, MD, PhD).