Neurodegenerative Disease after Head Trauma

Why does Head Trauma Increase the Risks of Neurologic Disease?

A percentage of individuals who experience head trauma and traumatic brain injury have an increased risk of developing a series of diseases classified as “neurodegenerative”.

Neurodegenerative is a term that describes a process in which nerve cells change their structure, lose their ability to function normally, or die off. When this happens, the physical, psychological, cognitive and emotional functions that those nerve cells controlled, no longer work in the same manner.

Current evidence suggests that for some individuals who suffered a moderate or severe head injury, there is an increased risk of developing dementia later in life. This body of evidence led the Institute of Medicine to report in 2009 that “there is sufficient evidence of an association between moderate and severe TBI and dementia”. 

One neurodegenerative disease that has been associated with head trauma is Alzheimer’s Disease. Other neurological diseases that have been reported by some scientific studies to develop after brain injury include Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS).

Alzheimer’s Disease

A number of research studies report that that a head trauma event which causes a loss of consciousness lasting longer than 24 hours, may be associated higher rates of dementia such as Alzheimer’s later in life. Although the evidence currently shows that there is a connection, that does not mean everyone who has sustained a head injury will develop Alzheimer's.

There appear to be other factors affecting this likelihood. For example, individuals who may be at a higher risk of Alzheimer's Disease after moderate to severe head injury often carry the apolipoprotein E (APOE) gene.  

Why Is Alzheimer’s Disease More Likely?

In addition to genetic predisposition, a key feature of Alzheimer’s disease is the appearance of something called “plaques” that reside around and in between nerve cells in the brain.

Plaques are formed from small pieces of protein which are called “beta-amyloid”.

These small clumps of beta-amyloid proteins are believed to interfere with communication between nerve cells. They also contribute to inflammation in the brain.

After brain injury, beta-amyloid protein levels go up in the brain, regardless of an individual’s age or overall state of health. In autopsy studies of individuals who died right after a brain injury, researchers found a 30% increase in the presence of beta-amyloid proteins.

It is possible that this increase in beta amyloid proteins may contribute to Alzheimer’s Disease development many years after head trauma. Scientists are still studying the exact mechanisms that cause beta-amyloid protein levels to rise, and how genetics and trauma interact to increase one's risk of dementia.

Parkinson’s Disease and Head Trauma

Symptoms of Parkinson's Disease (PD) include tremor, stiffness, slow movement (bradykinesia), inability to move (akinesia), shuffling walk, and stooped posture.

Parkinson's disease may develop years after TBI as a result of direct or indirect damage to the basal ganglia. The basal ganglia are a set of nerve cells between key brain structures. They help initiate and stop specific muscle movements.

Inflammation and generalized nerve cell death in the areas of the brain that control motor movements may also be part of the process leading to the development of Parkinson’s Disease; however, the research has some conflicting results about the relationship between PD and head trauma, so studies are ongoing to better understand the risk.

Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is also sometimes referred to as Lou Gherig’s disease. It is a degenerative disease that affects motor neurons, the nerve cells responsible for voluntary movement. Over time, the ability to move, speak, eat and breathe is lost.

Some studies have found that those with repeated head trauma, such as soccer players, are at a significantly increased risk of ALS later in life. However, researchers aren’t entirely sure what the physiologic process is behind ALS and head trauma, and urge caution in making this association until the process is better understood.  

Chronic Traumatic Encephalopathy

Repetitive mild brain injuries can lead to permanent brain damage.


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