Getting back to the specifics of the study by Guskiewicz at al., it is very important to note that the authors did not find a statistically significant association between repeated concussions and Alzheimer’s disease. What they found was a trend for retired NFL players to develop Alzheimer’s disease at an earlier age than the general American male population. However, this trend also normalized by age 75 such that there was no difference in Alzheimer disease rates between concussed subjects and controls. Unfortunately, some in the media have erroneously referred to MCI as “pre-Alzheimer’s” when the fact is that only a small subset of patients with MCI will actually develop Alzheimer’s disease each year, although at higher rates than the normal population. Not all patients with an MCI diagnosis will go on the develop Alzheimer’s disease and some of the patients with this diagnosis may be functioning within the range of normal variability given that even normal controls have been found to obtain low test scores (Marcopulos et al., 1997; Schretlen et al., 2003; 2008). In fact, recent studies (Brooks et al., 2007; Iverson et al., 2008) have shown that normal test performance is easily misdiagnosed as “mild cognitive impairment.” For example, Brooks et al. (2007) found that 57% of normal adults with low average intellectual functioning scored in the mild cognitive impairment range as did 21% of normal adults with high average intellectual functioning.

As alluded to earlier, one other factor that is very important to remember is that all brain injuries are not the same. This is perhaps one of the biggest mistakes I see some in the media and health care industry make. That is, they speak of traumatic brain injury (TBI) as if findings from studies with moderate to severe TBI patients can be applied to mild TBI patients. As noted in the prior link, moderate to severe TBI is very different from mild TBI and study findings are not interchangeable from one group to another. This is important to keep in mind when reading the study by Plassman et al. (2001), which showed an increased risk of Alzheimer’s disease among patients with moderate to severe TBI. However, I sometimes come across people who mention this study as if it means that the results can automatically be generalized to mild TBI. In fact, the study showed that attempts to associate mild TBI with dementia did not reach statistical significance.

Lastly, since patients may be concerned that a few repeat concussions will cause significant cognitive impairment, it is worth noting that there have been several studies performed which document no risk of cognitive impairment among active players who have suffered several concussions (Collie et al., 2006; Iverson et al., Pellman et al., 2004). For example, Collie et al. found no differences on computerized cognitive testing between patients who have suffered four concussions compared to no concussions. While these studies also have their limitations (e.g., relying on self-report for concussion diagnosis; not having all potential NFL players respond to the study) the study by Guskiewicz et al. also had these limitations. These studies are mentioned here to inform people that there are two sides to this issue, which the media rarely mentions or seems to dismiss if they are mentioned.

Although there have been some news reports and upcoming research studies based on autopsies of retired athletes from contact sports showing brain-related changes similar to that of Alzheimer’s disease, this really should not come as a surprise to anyone. The reason is because the scientific community has been aware of a condition referred to as dementia pugilistica since 1928, in which boxers develop dementia and related brain changes after suffering extensive mild traumatic brain injuries. In boxing, this usually occurs between 12-16 years after beginning a career. When conceptually extrapolating this information to football players who have been extensively concussed over a long playing career, such findings would not be unexpected. This is the case even in the case of an 18-year old football player with abnormal brain changes similar to those seen in Alzheimer’s disease, particularly if that individual has been playing for many years and has been exposed to extensive repetitive concussive injuries.

Ultimately, sports athletes should know that there is a known risk of cognitive impairment and brain-related changes after an extensive history of concussions over many years based on what is known about dementia pugilistica in boxers. At the same time, athletes should not be misled or scared into believing that one concussion or a few concussions (particularly if they are spread out significantly over time) increases the risk of cognitive impairment and dementia because the evidence is not available to support such a claim. MTBIFacts.com supports continuing research in this area but agrees with Guskiewicz and colleagues when they state that “…prospective longitudinal cohort studies are necessary to determine causality.” Case studies, while also important, cannot be generalized to the population at large.

REFERENCES

Collie et al. (2006). Does history of concussion affect current cognitive status? British Journal of Sports Medicine, 40, 550-551.

De Beaumont et al. (2009). Brain function decline in healthy retired athletes who sustained their last sports concussion in early adulthood. Brain, 132, 695-708.

Guskiewicz, K. et al. (2005). Association between recurrent concussion and late-life cognitive impairment in retired professional football players. Neurosurgery, 57, 719-726.

Iverson et al. (2006). No cumulative effects for one or two previous concussions. British Journal of Sports Medicine. 40, 72-75.

Marcopulos et al. (1997). Cognitive impairment or inadequate norms? A Study of healthy, older, rural adults with limited education. The Clinical Neuropsychologist, 11, 111-131.

Pellman et al. (2004). Concussion in professional football: Neuropsychological Testing – part 6. Neurosurgery, 55, 1290-1305.

Petersen R.C. et al. (2001). Early detection of dementia–-MCI (an evidence based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology, 56:1133–1142.

Plassman et al. (2000). Documented head injury in early adulthood and risk of Alzheimer’s disease and other dementias. Neurology, 55, 1158-1166.

Schretlen et al. (2003). Examining the range of normal intraindividual variability in neuropsychological test performance. Journal of the International Neuropsychological Society, 9, 864–870.

Schretlen et al. (2003). Frequency and bases of abnormal performance by healthy adults on neuropsychological testing. Journal of the International Neuropsychological Society, 14, 436–445.