Brain damage: Concussion linked to Alzheimer’s
Just in time for the college football championships, a new study relates prior concussion, current problems with memory or thinking, and subtle signs of encroaching Alzheimer’s disease.
Rapid acceleration of the head, whether in sports, accidents or war, can cause concussion, a swelling of the brain that brings on headache, confusion and “blacking out.” In the long term, a history of concussion has been linked to suicide, depression, dementia and a chronic traumatic encephalopathy, severe shrinkage of the brain tissue.
The concern over concussion has spread to boxing, hockey, soccer, rugby, and to soldiers struck by bomb blasts.
The new study, from the Mayo Clinic in Minnesota, looked at 589 people aged 70 to 89 who lived in Minnesota. About 24 percent of them had trouble with thinking and memory — called mild cognitive impairment. The rest had normal cognitive abilities. People with Alzheimer’s were not enrolled in the study.
Virtually the same percentage of both groups reported having lost consciousness at some time in their life due to head impact.
Reassuringly, that provided no reason to link blows to the brain with brain damage.
But brain scans for amyloid deposits, a type of toxic protein that is a hallmark of Alzheimer’s, told a different story. Measures of this chemical were 18 percent higher in people with cognitive difficulties who did recall a brain injury compared to those with normal thinking ability.
A head start
The study offered a version of the frustrating, “glass is half empty; no, it’s half full!” “The results are conflicting, interesting,” says study author Michelle Mielke, who works in neurology and epidemiology at Mayo. “We did not see any difference in the percentage of reported head trauma between the cognitive normals and the mild cognitive impairment.”
It’s possible, she says, that blows to the head had caused Alzheimer’s among people who then were excluded from the study, which would lead to an underestimate of the real effects of impact.
Another measure from the study – of the volume of the hippocampus, a brain structure intimately linked to memory that often shrinks in Alzheimer’s — did show a “trend” toward shrinkage, but the result did not achieve statistical significance.
“Our results add merit to the idea that concussion and Alzheimer’s disease brain pathology may be related,” said Mielke. “However, the fact that we did not find a relationship in those without memory and thinking problems suggests that any association between head trauma and amyloid is complex.”
Amyloid protein is either a cause, or an effect, or both, of Alzheimer’s, but the relationship remains murky. By age 70, 30 percent of individuals have a significant amount of amyloid, “but not all those individuals go on to develop Alzheimer’s,” Mielke says. “We think this does suggest that head trauma does increase one pathological hallmark of Alzheimer’s, but we can’t translate that to the odds of Alzheimer’s.”
As the pro football season grinds to a conclusion, the television documentary series Frontline reports 146 concussions and head injuries in the NFL this season. But Mielke emphasizes that those injuries tend to be much more severe than what happens in high school sports – the kind of injuries that were recalled by participants in the Mayo aging study. “A lot of times, when we talk about head trauma, concussion, we think of elite athletes in football and hockey.”
Trauma to the head “does not mean you are definitely going to develop mild cognitive impairment or amyloid plaques,” Mielke says, “and finding some people with MCI and high amyloid does not suggest that everybody is at risk.”
Instead, she says the study could indicate “that there are some individuals who are vulnerable to the head trauma, and will develop higher amyloid that puts them at greater risk of Alzheimer’s. We need to understand the mechanism and why some are more vulnerable than others.”
– David J. Tenenbaum
Terry Devitt, editor; S.V. Medaris, designer/illustrator; Yilang Peng, project assistant; David J. Tenenbaum, feature writer; Amy Toburen, content development executive
- Head trauma and in vivo measures of amyloid and neurodegeneration in a population-based study, Michelle Mielke et al, Neurology 82, January 7, 2014. ↩
- UCLA study reveals abnormal brain proteins related to concussion in retired NFL players. ↩
- Frontline explores Brain Damage in Living Ex-NFL Players. ↩
- Pro Football Hall of Famer Tony Dorsett talks about living with CTE (chronic traumatic encephalopathy). ↩
- Shortage of donated brains slows research ↩
- Concussion symptoms and signs at Mayo Clinic ↩