In the latest research diving into long term consequences of serial head injury a study was published in the Journal of Neurotrauma finding that “Three or more mTBI associated with significant cognitive deficits“.
In the study, titled “Lifetime Traumatic Brain Injury and Cognitive Domain Deficits in Late Life: The PROTECT-TBI Cohort Study” the authors had participants complete cognitive assessments annually for 4 years. The participants were canvassed for their history of traumatic brain injuries. The participants were between 50 and 90 years of age with most not reporting a recent head injury for decades. The study sought to find what issues those with historic head injuries had compared to those without.
Across many measures those with historic concussions faired poorer than those without with 3 or more previous concussions being a strong linked with “significant cognitive deficits” later in life. On this issue the researchers noted as follows:
Three or more mTBI associated with significant cognitive deficits
This study found that those who reported 3 mTBIs had significantly worse executive function and attention scores, and those who reported 4+ mTBIs had worsened attention, processing speed, and working memory. Whereas most studies for repeated mTBI have focussed on young athletes in the acute or subacute phase (<3 months post-TBI) this study examined the mid to late life general population largely in the chronic phase of TBI (>3 months post-TBI). This is a critically important result. It gives a clear threshold at which mid to late life cognitive deficits can be realistically expected. Legal regulations and medical guidelines around when to stop higher-risk activities, such as contact sports, are hotly debated.45 Most experts agree that recommendations to cease the higher-risk activity should be case by case depending upon the severity of the injury, the extent of the ongoing deficits, and the force of subsequent TBI-inducing force (vis-a-vis “fighter’s chin” syndrome46).
However, such assessments can be insensitive to small effects, often lack a pre-TBI baseline, and assess current rather than future function. When making recommendations for those who have suffered recurrent TBI, clinicians should be cognizant that some long-term cognitive deficits can be expected after 3 or more mTBIs. Although the effect sizes for the cognitive deficits at 3 or 4+ mTBIs were small (i.e., all B < 0.2), the effects were dose-dependent. That is, the deficit increased step-wise with increased numbers of reported mTBIs (see Tables 3 and 4) and thus recommendations should indicate that each additional mTBI increases risk of substantial cognitive decline. As previously mentioned, there was no greater decline in cognitive scores with time in this study for those with higher numbers of mTBIs, suggesting that in the chronic phase mTBI causes a dose-dependent, fixed cognitive deficit.
The full abstract reads as follows:
Traumatic brain injury (TBI) causes cognitive impairment but it remains contested regarding which cognitive domains are most affected. Further, moderate-severe TBI is known to be deleterious, but studies of mild TBI (mTBI) show a greater mix of negative and positive findings. This study examines the longer-term cognitive effects of TBI severity and number of mTBIs in later life. We examined a subset (n = 15,764) of the PROTECT study, a cohort assessing risk factors for cognitive decline (ages between 50 and 90 years). Participants completed cognitive assessments annually for 4 years. Cognitive tests were grouped using a principal components analysis (PCA) into working memory, episodic memory, attention, processing speed, and executive function. Lifetime TBI severity and number were retrospectively recalled by participants using the Brain Injury Screening Questionnaire (BISQ). Linear mixed models (LMMs) examined the effect of severity of head injury (non-TBI head strike, mTBI, and moderate-severe TBI) and number of mTBI at baseline and over time. mTBI was considered as a continuous and categorical variable (groups: 0 mTBI, 1 mTBI, 2 mTBIs, 3 mTBIs, and 4+ mTBIs). Of the participants 5725 (36.3%) reported at least one mTBI and 510 (3.2%) at least one moderate-severe TBI, whereas 3711 (23.5%) had suffered at worst a non-TBI head strike and 5818 (32.9%) reported no head injuries. The participants had suffered their last reported head injury an average (standard deviation, SD) of 29.6 (20.0) years prior to the study. Regarding outcomes, there was no worsening in longitudinal cognitive trajectories over the study duration but at baseline there were significant cognitive deficits associated with TBI. At baseline, compared with those without head injury, individuals reporting at least one moderate-severe TBI had significantly poorer attention (B = −0.163, p< 0.001), executive scores (B = −0.151, p = 0.004), and processing speed (B = −0.075, p = 0.033). Those who had suffered at least a single mTBI also demonstrated significantly poorer attention scores at baseline compared with the no head injury group (B = −0.052, p = 0.001). Compared with those with no mTBI, those in the 3 mTBI group manifested poorer baseline executive function (B = −0.149, p = 0.025) and attention scores (B = −0.085, p = 0.015). At baseline, those who had suffered four or more mTBIs demonstrated poorer attention (B = −0.135, p < 0.001), processing speed (B = −0.072, p = 0.009), and working memory (B = −0.052, p = 0.036), compared with those reporting no mTBI. TBI is associated with fixed, dose, and severity-dependent cognitive deficits. The most sensitive cognitive domains are attention and executive function, with approximately double the effect compared with processing speed and working memory. Post-TBI cognitive rehabilitation should be targeted appropriately to domain-specific effects. Significant long-term cognitive deficits were associated with three or more lifetime mTBIs, a critical consideration when counseling individuals post-TBI about continuing high-risk activities.