"We classify patients into possible or probable CTE," neurologist Dr Rowena Mobbs, an expert in concussion injuries from Macquarie University, said. The reason there is no "definite" category is because the disease can only be diagnosed after death, through analysis of brain tissue. The development of CTE is associated with repeated head trauma, like concussion. But little is known about how many knocks can cause it, or how hard those knocks really need to be. This is because CTE can also be caused by "subconcussive impacts", which are smaller head knocks that don't lead to a loss of consciousness but can still damage the brain over time. "Subconcussion is when there are no symptoms at all from a head knock. Those little repetitive head knocks can add up," Dr Mobbs said.
Laura Kewley and Paul Kennedy, 'Julie suffered 60 concussions during her sporting career. At age 54, her brain has been permanently damaged', ABC