What are the long-term effects of a head injury?
From traffic accidents to collision sports, millions of people around the world experience head injuries every year.
People often tend to think of brain injury as a distinct event that causes damage and then that’s the end of the story.
While these injuries can result in immediate damage to the brain, evidence suggests that they could also have significant effects in the longer-term.
Traumatic brain injury, otherwise known as TBI, is now widely recognised as a risk factor for dementia.
Studies have shed light on higher rates of dementia in people who sustain these injuries, but we don’t yet fully understand how these events set dementia-causing processes in motion.
However, understanding the long-term consequences of a head injury and the changes that lead to an increased risk of dementia is an important goal for research.
Traumatic brain injury
While there is a strong link between traumatic brain injury and dementia, it is difficult to predict which patients might be affected in this way.
As a neurology doctor at St Mary’s Hospital, London, I research and develop new ways to help the patients that I treat in hospital, with Professor David Sharp who leads the clinical and research teams in TBI.
There is a growing awareness of neurodegenerative problems, such as ‘chronic traumatic encephaloapthy’ after injury, particularly in the setting of repeated mild injuries, but many of the same brain changes can be produced by single moderate/severe injury. We know that a single injury can trigger long-term processes that cause the brain to shrink over many years after the injury took place.
Head injury can set in motion some of the hallmark processes of dementia, such as accumulation of harmful proteins.
But there is more evidence to suggest that the picture is much more complicated than that.
Alongside a team at the UK Dementia Research Institute, we looked at a particular type of injury called diffuse axonal injury.
This type of injury takes place when the shearing forces sustained during head injury damage or sever nerve fibres in the brain’s white matter. The white matter is found deep inside the brain and contains the parts of brain cells that carry messages from one area of the brain to another, allowing us to do everything we usually do like eat, move and talk.
To investigate this further we took use of advanced imaging technology to study the mechanisms linking brain injury and dementia.
What we did
Using advanced MRI brain scanning techniques we investigated changes over time in 55 people after moderate to severe traumatic brain injury. We then compared them to 19 people who did not have a head injury.
A first scan measured the size of the brain and then a special type of scan was used to measure damage to the axons within the brain.
Participants were scanned a year later to see where and how much the brain had shrunk in size, and how that related to the amount and location of axonal damage on the first scan.
We found the amount of white matter damage measured at the first scan could be used to reliably predict shrinkage over the next year. The areas with the most shrinkage were those regions which had the greatest damage at the initial scan.
People with higher rates of brain shrinkage performed more poorly on memory tests.
Why does this matter?
If we can predict what changes might happen in the brain long after a head injury occurs, we are in a much better position to intervene than, say, if we wait 30 years until someone may develop dementia.
Our results showed that the extent and location of damage is a strong predictor of the amount and pattern of nerve cell loss.
The results of the experiments suggest that, by assessing of the scale and location of this type of injury using imaging techniques, the risk of long-term neurodegeneration in an individual can be more reliably assessed.
This could help to identify suitable candidates for clinical treatment trials, with the aim of preventing dementia following a head injury.
Being able to accurately diagnose the nature of a head injury will improve quality of life and health of TBI patients by providing greater certainty about what to expect.
An accurate diagnosis will assist patients and their families in adapting to life after their injury and ensure that treatment and care can be better targeted to an individual’s needs.
In addition, we hope the approach will provide a means of addressing some of the increasing concerns about the long-term effects of repeated mild injuries, for example in the sporting setting.
COVID-19 and dementia
Now, more than ever, we should consider the ways in which we can support people and their families so that this group of people are not left behind.
To help as many people as possible we really need to address prevention as well as life-changing dementia treatments.
Research has been put at risk by COVID-19 with one in three dementia researchers thinking of leaving the field.
Alzheimer’s Research UK fund Dr Neil Grahams work and this is only made possible by you, our fantastic supporters. Please consider donating.
About the author
Dr Neil Graham is an Alzheimer’s Research UK Clinical Research Fellow at the Division of Brain Sciences, Imperial College London. He studied medicine at Cambridge and University College London, developing an interest in acquired brain injury during training posts at St Thomas' Hospital and the National Hospital for Neurology and Neurosurgery. His research interest is the relationship of traumatic brain injury (TBI) to dementia. Supervised by Prof David Sharp, he is focused on the development of imaging tools that can measure brain degeneration in patients after TBI. He is aiming to improve our ability to diagnose significant head injuries when they take place and working towards treatments that could prevent brain degeneration after injury.