WHEN the 2013 National Football League season kicks off in the US next month, players will have an added layer of protection to go with their helmets and shoulder pads: an independent neurologist at every game to assess them for signs of concussion after receiving a blow to the head.
Head injuries are an occupational hazard for American footballers and a major issue for the NFL. Thousands of retired players are suing the league for negligence and fraud, claiming that the league knew about the long-term risks but hid them.
The condition they fear is chronic traumatic encephalopathy (CTE), previously called punch drunk syndrome, boxer’s dementia or dementia pugilistica. This causes progressive memory problems, personality change and slowness of movement. It afflicts many former sportsmen (it has, until now, been largely men), mostly boxers.
The pathology of CTE is well known. In the 1980s, John Corsellis of the Maudsley Hospital in London documented it in a series of papers, culminating in a 1989 review in the BMJ.
He found that many nerve fibres showed evidence of tearing, with some being completely torn, and also reported widespread brain degeneration. He also described how many neurons were filled with tangles of protein, one of the hallmarks of Alzheimer’s disease.
Other researchers later showed that the brains of men with CTE had a second type of protein deposit called amyloid, another hallmark of Alzheimer’s.
While there is no doubt that these problems are caused by repeated blows to the head, until recently it wasn’t known how.
Blows to the head cause two different kinds of injury. The face is cut and bruised by direct impacts, but damage to the brain is caused largely by rotational acceleration of the cerebral cortex around the much smaller midbrain and spinal cord. This damage may be aggravated by boxing gloves since they add weight and thus energy to punches, causing more rotational acceleration.
Brain tissue is largely a soft mass but the blood vessels within it are fibrous and strong, like wires across cheese. When the head is hit, especially with a rotational movement, one of two things can happen. Either a blood vessel can snap, leading to a haemorrhage, or there can be microscopic tearing of the tissue around the vessel.
Large haemorrhages are what cause boxers to fall into comas and occasionally die during bouts, but the microscopic tears to blood vessels can be no less damaging in the long run.
The first thing to note is that sportsmen who were frequently injured in this way in their youth often develop characteristic behaviour patterns as they get older. These are the problems often reported in lurid stories about troubled ex-boxers: depression, drug and alcohol abuse and violent tempers. All are consistent with underlying damage to the frontal cortex, which controls executive functions such as impulse control.
This is not to say that all ex-sportsmen with these problems have CTE, but it is clear that in some cases it is a contributing factor.
What’s more, recent experiments in mice have indicated that protein tangles and amyloid deposits can slowly spread from neuron to neuron. The distribution of the tangles in CTE is consistent with this, forming first around blood vessels before spreading.
With these findings we can now formulate a plausible hypothesis as to why repeat head injuries to young men in their teens and 20s lead to personality changes later in adult life and dementia in old age: rotational head injury induces damage, especially around blood vessels, leading to local tangle formation, followed by a slow spread of destruction.
Clearly, considerable effort should be expended in all sports to minimise head injuries. Soccer has already done the right thing by replacing heavy leather balls with lighter plastic-coated ones. American football appears to be going in the right direction. But other sports have some way to go.
In ice hockey, the role of the “enforcer”, whose main job appears to be beating up the opposing team’s players, should be abolished. And in all sports where there is any risk of head injury – rugby for example – players should be monitored to keep an eye on the damage. Clearly, all who play and coach these sports should be aware of the risks.
Boxing, however, is a special case. No other sport has the express goal of causing injury to the brain. That is certainly the aim of professional boxing. Even in amateur boxing blows to the head are crucial, and protective headgear may not stop injury from rotational acceleration.