Concussion's Long-term Consequences
Recovering from concussion
In terms of short-term recovery, the brain changes that occur after a single concussion don’t appear to have clear long-term cognitive effects. Return to contact sport should be gradual: the ‘if in doubt, sit it out’ rule-of-thumb is now adhered to by many sporting codes.
A very small percentage of people who sustain a concussion go on to develop what is known as post-concussion syndrome. Symptoms usually develop seven to 10 days after a concussion, and can persist for weeks, months, and sometimes years. Why the syndrome occurs remains unclear. This was the experience of Australian tennis player Casey Dellacqua.
Dellacqua, who suffered a heavy on-court fall in October 2015, wrote in a blog post that post-concussion syndrome was “honestly some of the scariest stuff” she had experienced. Her symptoms included headaches, inability to sleep, memory problems and constant drowsiness. “I was so desperate to just feel myself again but I struggled to do even daily activities such as the grocery shopping,” she wrote.
The long-term consequences of concussion
While the short-term symptoms of concussion are reversible, research suggests that even a single knock to the head can have severe consequences later in life. For example, figures from one study that analysed the records of more than 160,000 trauma patients identified that, in patients aged 65 and older, just one concussion was associated with a 22-26% increase in dementia risk in the following five to seven years.
Even clearer is research showing that neurological damage accumulates with multiple knocks to the head, even when they are apparently symptomless, or ‘sub-concussive’. Repeated concussion has been linked to increased risk of neurodegenerative conditions such as Alzheimer’s and Parkinson’s disease, as well as chronic traumatic encephalopathy (CTE).
Data from studies of former American footballers is staggering. A survey of more than 2000 retired professional players found that those with a history of multiple concussions were three times more likely to have been diagnosed with clinical depression. Another study of death certificates found that the death rate from neurodegenerative diseases was three times higher for pro-footballers than the general population.
When should you seek medical advice for concussion?
Because the symptoms usually resolve by themselves, a concussion is best managed with physical and cognitive rest. However, stories about the potentially tragic consequences of undetected brain injuries are difficult to ignore. Symptoms of severe TBI can develop over several hours. Therefore, after a knock to the head, it’s important to be alert for the first 24 hours. Some symptoms are red flags for more severe brain injury: if a head injury results in a loss of consciousness, increasing confusion, vomiting or a worsening headache, the person should seek medical advice. It’s important that a doctor makes an assessment to rule out more severe TBI.
What is Chronic Traumatic Encephalopathy (CTE)?
There is now evidence that repeated concussions could be associated with the development in later life of a particular kind of degenerative disease called chronic traumatic encephalopathy (CTE).
CTE is a progressive disease with Alzheimer’s-like symptoms. It was first discovered by neuropathologist Dr Bennet Omalu in the early 2000s in the brain of Mike Webster, a former National Football League (NFL) player. When Omalu looked at Webster’s brain tissue under the microscope he observed concentrations of a material known as tau. This is one of two proteins known to accumulate in the brain in Alzheimer’s disease. Since then, CTE has been found in the brains of 76 out of 79 former NFL players who have donated their brains to research.
CTE has many of the same physiological hallmarks of forms of dementia, including Alzheimer’s disease, particularly the abnormal accumulation in the brain of a protein called tau. In a healthy brain, tau is found in the axons – the transmission lines – of neurons, where it plays an important role in maintaining the structure of the internal transport system of these nerve cells. In conditions such as Alzheimer’s and CTE, tau instead forms tangles that clump together to disrupt the cells’ transport system. These are known as neurofibrillary tangles and sometimes simply tau tangles. They’re a cellular signpost of what are known as tauopathies: the group of degenerative diseases associated with aggregations of tau protein in the brain. These tangles are thought to eventually lead to the death of neurons. As more and more neurons die and large areas of brain tissue become affected, dementia symptoms appear: memory loss, confusion, Parkinson’s-like tremors, walking problems, impaired judgement, depression and personality changes.
The need for early CTE diagnosis
Repeated head trauma doesn’t always lead to CTE and it is likely a person’s genetic background also plays a role. Currently, the only way to diagnose CTE is post-mortem, which means it’s impossible to determine how prevalent the condition is in the general population or catch the condition at an early stage. The next challenge for TBI researchers is to develop techniques that can identify CTE in living brains. QBI’s Dr Fatima Nasrallah is using the support of a Motor Accident Insurance Commission Senior Research Fellowship to work on TBI, specifically to try and develop an early diagnostic test for concussion. She hopes to use biomarkers and imaging to develop a test that will be able to detect even subtle changes in brain function following a head injury.
CTE research brings more questions
It’s only since the early 2000s that CTE has been linked to concussion and, not surprisingly, there is still much work to be done in understanding the relationship between the two. We are, however, only just developing ways to see tau using imaging techniques such as positron emission tomography or PET. One major difficulty with studying CTE is that the only definitive way to make a diagnosis is by autopsy – looking at people’s brains after they’ve died.
We also don’t know how many or what type of concussions it takes for someone to develop CTE or how long it takes for the disorder to appear. Most importantly, we don’t know what can be done to prevent or reverse the damage.
The presence of abnormal tau tangles does offer a diagnostic and therapeutic target, just as it does in other tauopathies such as dementia and Alzheimer’s. Researchers like QBI’s Professor Jürgen Götz are exploring ways to remove the tau tangles, while others are focusing on imaging techniques that can reveal tau when CTE is still in its early stages, offering a greater chance of treatment.
Concussion from a freak accident while competing in a doubles tournament in Beijing, in October 2015, forced Australian tennis player Casey Dellacqua out of the game indefinitely in 2016.
CTE was first discovered by neuropathologist Dr Bennet Omalu in the brain tissue of former NFL player Mike Webster. Their story has been depicted in the motion picture Concussion.
In 2015, the QBI team led by Professor Jürgen Götz (pictured above) announced one of the most exciting recent breakthroughs in Alzheimer’s disease research, one that is likely to also have consequences for concussion.
They discovered that ultrasound – as used to view babies in the womb – can also trigger the brain's own waste disposal system to clean up deposits of a protein known as beta-amyloid in the brains of mice with Alzheimer’s disease (AD). These protein deposits are called amyloid plaques, and along with tau tangles, are a key feature of AD.
The team found that injecting safe microbubbles into the bloodstream and then pulsing the brain with ultrasound caused the impermeable blood-brain barrier to open temporarily. This opening is thought to activate microglia, resident garbage collector cells, which clean up waste products in the brain.
Professor Götz’s team found that the ultrasound method reduced the amount of abnormal protein and was also linked with improvements in the memory of mice with AD. The challenge now is to translate such a method to the human brain, but Professor Götz and colleagues in this field around the world are excited about the potential.