Brain injury specialist Dr Willie Stewart told BBC Radio Scotland on Sunday the brains of head-injury victims looked similar through a microscope to people with dementia.
The neuropathologist examined the brain tissue of a former rugby player for abnormal proteins associated with head injuries and dementia, confirming what he believed to be the first confirmed case of early-onset dementia caused by playing rugby.
Dr Stewart said sports such as rugby and American football were beginning to lead to problems later in life normally suffered by former boxers.
Dementia pugilistica, also known as punch-drunk syndrome, mainly affects the frontal lobe and symptoms can include memory and speech problems, trembling and a lack of coordination.
Symptoms usually appear 12-16 years after the boxer’s career begins and about 15-20 per cent of professional boxers are thought to develop it.