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A mythical belief that remains pervasive in the minds of the general public is that a single mild traumatic brain injury (concussion) can lead to permanent cognitive impairment or dementia (e.g., Alzheimer’s disease) when there is not a single prospective research study showing this to be the case. The concern about this topic appears to stem from misinterpretations about a study published in 2005 by Guskiewicz and colleagues which showed that concussions increased the risk for long-term cognitive impairment. However, what many people do not realize and what many in the media omit is that the increased risk of cognitive impairment in that study occurred in the context of recurrent concussions.
That is, experiencing three or more concussions (not one) appeared to increase the risk for long-term cognitive impairment in that study. Furthermore, the risk solely occurred in the context of professional football players who were exposed to massive collisional forces over the course of their playing career. Therefore, generalizing these finding to the general population may not be appropriate. In addition, there is no evidence that one can equate cognitive impairment risk caused by multiple concussions in professional football players (which may occur before the prior injury has healed) to those who suffered multiple concussions spread out over decades of their life (e.g., ages 10, 25, and 35).
Overall, the fact is that the evidence from the sports concussion literature and numerous meta-analyses (which combine the results of many studies together) show that a single concussion does not cause long-term cognitive impairment. The interested reader is encouraged to read the book referenced below by McCrea (2008) which summarizes these various studies and to see the article on this website about “postconcussion syndrome” where many references over the past few decades on this topic are listed.
Given the above, it makes sense that some are interested a 2009 study by De Beaumont et al. In this retrospective study, the authors claimed that a single concussion can lead to long-term cognitive impairment three decades later. The problem is that this conclusion runs counter to decades of research on this topic that utilized much stronger research designs to assess this issue. No firm conclusions can be made about the effects of concussions on cognition without carefully controlled prospective studies. Such studies have been performed and are discussed here and in McCrae (2008).
For readers unfamiliar with research methods, a prospective study is one in which the research design is thought of in advance of data collection and patients are followed from before injury or from the time on injury forwards. This is a much stronger type of research design because the researcher can track the subject from the onset of an injury, leaving no doubt as to how the patient initially presented and was functioning at the time. The researcher also has better control and knowledge of intervening events that can confound subsequent data analysis since he/she would be interacting with the patient periodically.
Other problems with the study is that no data was collected to assess for the current effects of depression and other psychiatric factors on the test results. This is crucial because it may be that depressed patients are more prone to recall past negative events (e.g., head trauma) compared to healthy controls. In addition, no assessment of effort was performed to ensure the reliability and validity of the data. This is also crucial because depressed patients (or any patient for that matter) exerting poor effort on testing will yield distorted neuropsychological test data (Rohling et al., 2002).
The study also mixes singly concussed patients with patients who had multiple concussions (up to five), although most were singly concussed. Nevertheless, generalizations about singly concussed patients should come from a data set that exclusively contains singly concussed patients. The experimental group only included 19 patients, which is too few patients to make broad generalizations about. Despite all of these problems, when one examines the 11 cognitive tests administered, the authors only found a statistically significant difference at (<.05 alpha level) in two of them when concussed and non-concussed groups were compared. This includes only a one point difference on a delayed visual-spatial recognition memory test. A one point difference on this test (which I use regularly in my practice) has no clinical significance. To take a one point difference like this and to then make the argument that this may somehow be related to Alzheimer’s disease is a significant overstatement of the data. The other difference was on a research task that has not been validated for clinical purposes, and which was modified from the original 1974 research version.
Lastly, another fact glossed over in news reports about this study is that the authors stated that “None of the motor or cognitive measures that were found to be significantly altered in former athletes with concussions correlated either with the number of concussions sustained, the time elapsed since the last concussion or the severity of concussions sustained.”
REFERENCES
DeBeaumont et al (2009). Brain function decline in healthy retired athletes who sustained their last sports concussion in early adulthood. Brain,
Guskiewicz et al. (2005). Association between recurrent concussion and late-life cognitive impairment in retired professional football players. Neurosurgery, 57, 719-726.
Lees-Haley et al. (2001). A comparison of complaints by mild brain injury claimants and other claimants describing subjective experiences immediately following their injury. Archives of Clinical Neuropsychology,16, 689–695.
McCrea, M. (2008). Mild traumatic brain injury and postconcussion syndrome. The new evidence base for diagnosis and treatment. New York: Oxford University Press.
Rohling et al. (2002). Depressive symptoms and neurocognitive test scores in
patients passing symptom validity tests. Archives of Clinical Neuropsychology
17, 205–222
Dr. Carone offers lectures on MTBI, “post concussion syndrome,” and symptom validity testing upon request. He can be contacted at info@mtbifacts.com.
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