New research has found that a protein indicating the breakdown of white matter in the brain can be detected following a hard blow to the head, raising hopes that a blood test could soon detect a concussion, predict how long symptoms will linger, and guide decisions about an athlete's return to play.
In their bid to find a blood "biomarker" for concussion, researchers went to a sport with plenty of blood and plenty of concussions: hockey. For the first half of the 2012-13 hockey season, they gathered blood samples and tracked blows to the head among the 288 professional hockey players of the Swedish Hockey League. Between September 13, 2012, and Jan. 31, 2013, 35 suffered a concussion, and 28 of those had blood samples taken 1, 12, 35 and 144 hours after their injury.
Elevated levels of the protein known as total-tau, or T-tau, have long been seen as a marker for brain injury, and are present in a wide range of neurodegenerative disorders, including Alzheimer's disease.
The latest study, published in the journal JAMA Neurology, finds that T-tau levels spiked in the blood in the hour after a hockey player suffered a traumatic brain injury, and then again about 36 hours later. And while they declined slightly in between and after 36 hours, blood samples of players with concussions showed elevated levels of T-tau six days after their injuries, compared with blood samples taken in the pre-season. The higher a player's T-tau level was in the first hour after injury, the longer it took for his concussion symptoms to fade away, researchers found.
While researchers suspected T-tau might be key to diagnosing concussions, detecting elevated T-tau levels is more easily said than done: With varying degrees of accuracy, it can be done by drawing cerebro-spinal fluid from the brain's fluid-filled ventricles, or from spinal fluid. Jabbing a plunger into the brain or the spine is riskier and more expensive than drawing blood and testing it, but no existing blood assays were capable of detecting elevated T-tau levels.
Then, in 2012, two of the study's co-authors, from Quanterix Corp. in Massachusetts, pilot-tested a highly sensitive new immunoassay. They found it capable of detecting heightened T-tau levels in the blood of patients who had hypoxic injuries to the brain after a heart attack. The same assay was used to compare players' blood levels of T-tau from the pre-season to those immediately after a blow to the head.
The same researchers found two other potential biomarkers of little use in distinguishing those who sustained concussion from those who did not.
In an editorial accompanying the Swedish hockey study, a pair of brain scientists cautioned that T-tau is a sign of only one kind of injury that takes place in concussion: the twisting and stretching of axons, the fibers that carry electrical signals between cells and among different regions in the brain. If a blood test is to capture all concussions, wrote Joshua Gatson and Dr. Ramon Diaz-Arrastia, it may also need to look for markers that reveal injury to the brain's blood vessels, its specialized immune system and its diverse "helper" cells.
Gatson is a professor of surgery at University of Texas Southwestern Medical Center, and Diaz-Arrastia is a professor of neurology and regenerative medicine at the Uniformed Services University of the Health Sciences in Bethesda, Md. The lead authors of the hockey study are at University of Gothenburg in Sweden and Sahlgrenska University Hospital.
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