LONDON (Reuters) - Rugby and soccer players who suffer multiple knocks to the head during their careers are at added risk of brain damage that could lead to dementia and other neurodegenerative diseases, brain scientists are warning.
Just as some American football players and boxers have been found to have long-term cognitive deficits after suffering repeated head blows or concussions during play, so soccer and rugby players must be made aware of the same dangers.
"What happens is that when you have a big impact, your skull twists one way but your brain stays in the same place," said John Hardy, chair of Molecular Biology of Neurological Disease at University College London's Institute of Neurology.
These injuries, he said, common among boxers, American National Football League (NFL) and ice hockey players, as well as soccer and rugby players, can cause damage to the brain similar to abnormalities found in people with Alzheimer's disease and other forms of dementia.
"We need to minimize the risks by coming down very heavily on tackles and behaviors that are likely to cause rotational injury to the brain," Hardy said.
Such concerns have echoed across sport in recent days, particularly after English soccer club Tottenham Hotspur controversially allowed goalkeeper Hugo Lloris to play on even after he was knocked out in a collision with a striker.
Luke Griggs, a spokesman for the brain injury charity Headway, said the decision displayed an "irresponsible and cavalier attitude to a player's health". By playing on, he said, Lloris may have caused greater damage to his brain.
"He should have been removed from the game immediately and taken to hospital for thorough tests and observation."
Brain scientists and medical experts agree.
At an international conference on concussion in sport last year, specialist doctors working in sport drafted a consensus saying that no player, regardless of the sport, should return to the field of play on the day of a concussive injury.
Yet the problem there, says Willie Stewart, a consultant neuropathologist at Glasgow's Southern General Hospital who is due to speak at a professional rugby concussion forum in London this week, is that diagnosing concussion is a far lengthier and more complex process than many people assume.
"People believe you have to be knocked unconscious to have concussion, but there are many other symptoms of concussion too," Stewart told Reuters in an interview.
These include headaches, nausea, lack of awareness and blurred or confused vision - but some, many, or all of these symptoms may not appear straight away, he said, and often take hours or even days to appear.
Which makes a five-minute pitch side assessment, be it in rugby, soccer, NFL or elsewhere, a fairly unhelpful approach if an accurate diagnosis is to be made.
"The rule should be 'if in doubt, sit them out'," said Stewart." And if you have enough suspicion that a player is concussed to want to conduct a pitch side assessment, then there's enough doubt there already to take them out of play."
Stewart and Hardy both called for more education and awareness of the symptoms of concussion, its risks, and the possible long-term damage it can cause.
While relatively few studies have been conducted in rugby players, American footballers and boxers have been presented with new and disturbing evidence in recent years, partly thanks to advances in modern neuroscience which mean scientists know more than ever about chronic brain damage.
It has various names - including punch drunk syndrome, dementia pugilistica and chronic traumatic encephalopathy (CTE) - but comes down to the same thing: The long-term trauma that can result from frequent knocks to the head.
Hardy explains that within the soft mass of the brain tissue, the blood vessels are more fibrous and strong - a bit like wires. When the head is hit, especially in a rotational movement, one of two things can happen - either the blood vessel can snap, leading to a hemorrhage, or there can be microscopic tearing of the tissue around the vessel.
It is this microscopic damage, often not picked up by doctors at pitch side, or even noticed by the players, that is the most likely cause of long-term brain harm.
Such findings are not just in men. A small study of female soccer players published earlier this year found evidence of "mild traumatic brain injury of the frontal lobes" caused by repeatedly bouncing a football off the head.
Hardy, whose main concern is about boxing - which he describes as little more than "watching people inflict brain damage on each other" - says he was horrified to see women's boxing at the London 2012 Olympic Games.
Stewart says the key issue is the brain, not the sport, the person, their age or their gender.
"A brain injury is a brain injury is a brain injury," he said. "When it gets injured, the brain has no idea what sport it's playing or where it is."
Reporting by Kate Kelland, editing by Pritha Sarkar