Chronic neuroinflammation after head injury has been linked to neurodegeneration. Research suggests that this persistent neuroinflammation after central nervous system (CNS) injury may result from an autoimmune response to the normally immunoprivileged CNS ― and that it could cause or contribute to chronic traumatic encephalopathy (CTE). The phenomenon isn’t fully understood, however.

“In the future we may be able to do antemortem studies where we can actually quantitate the number of inflammatory cells in the human brain,” says Cleveland Clinic neurosurgeon Gregory Hawryluk, MD, PhD, Medical Director and Chair of the Scientific Advisory Board of the Brain Trauma Foundation. “At the moment, however, our difficulty studying the autoimmune response to CNS injuries has limited our consideration of this phenomenon, even though it should be an obvious candidate for dementias such as CTE.”

In the latest episode of Cleveland Clinic’s Neuro Pathways podcast, Dr. Hawryluk discusses current knowledge about autoimmunity following brain and spinal injuries and makes a case for ramping up investigations into the CNS-directed autoimmune response. He covers:

• The importance of challenging conventional thinking in head injury and within neurosurgery
• Findings from autopsy studies of people who have had head injuries
• Measuring neuroinflammation in people with brain trauma and spinal cord injury
• Preclinical and patient studies that point to the impact of autoimmunity after head injury
• Severe trauma, repetitive microtraumas and the additive effect of trauma on CNS autoimmunity

Click the podcast player above to listen to the 29-minute episode now, or read on for a short edited excerpt. Check out more Neuro Pathways episodes at clevelandclinic.org/neuropodcast or wherever you get your podcasts.

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Excerpt from the podcast

Dr. Hawryluk: It’s now very well established that brain proteins enter the bloodstream after a head injury. In fact, this has translated to FDA approval of a point-of-care test a couple of years ago. There is proof beyond a shadow of a doubt that head injury spills brain proteins ― immune-privileged antigens ― into your blood. Moreover, the worse your head injury, the more you spill. It’s very interesting.

It’s possible that this autoimmunity may tie a lot of things together. A fascinating potential example of this is related to the issue of the transmissibility of Alzheimer’s disease. It used to be that if you had pituitary dysfunction and you needed growth hormone supplementation ― this was before we had recombinant technologies and could make these proteins in a lab ― you had to take cadaveric sources. And undoubtedly there was some brain contamination in those specimens. There was a very high-profile paper a number of years ago that raised the possibility that some of these patients who were receiving human growth hormone supplements, it seemed like they were all of a sudden developing Alzheimer’s disease.

I want to be clear that it’s absolutely possible that there’s something transmissible about Alzheimer’s disease. But an alternate explanation could be that it’s simply an autoimmune response that’s damaging the brain, leading to cognitive decline. So it’s a case of circumstantial evidence, of Alzheimer’s being slapped onto something where maybe it shouldn’t be.

I often find, if you peel back the layers on these things and you start to consider that possibility that an autoimmune attack to the brain after some form of brain injury could be problematic, it potentially could explain an awful lot of things.