Among mysterious celebrity deaths, it is up there with JFK and Elvis. But the myth of Bruce Lee's demise in Hong Kong in 1973 may finally have been solved.

"The death of Bruce Lee, coming at such a young age and in the peak of physical fitness, has given rise to much speculation," said James Filkins, at Cook County medical examiner's office in Chicago. "Almost as soon as Lee died rumours began to surface."

The official cause of Lee's death was recorded in the autopsy report as cerebral oedema, or brain swelling. This was supposedly due to his hypersensitivity to a painkiller called equigesic that he had taken that day. But further research suggests the kung fu idol may have died from an epileptic condition first recognised more than 20 years after his death.

Dr Filkins thinks the official explanation is also wrong. Drug reactions tend to involve an anaphylactic reaction in which the victim's neck swells, he told the annual meeting of the American Academy of Sciences in Seattle. Instead, he thinks Lee died of a condition called sudden unexpected death in epilepsy (SUDEP), which was only recognised in 1995.

Jane Hanna, director of the support charity Epilepsy Bereaved, said SUDEP was gaining recognition. "Ten years of campaigning to influence decision makers has seen a seismic shift in thinking and practice on SUDEP in the UK," she said. "[But] we remain urgently concerned that prevention strategies are not being implemented and that young people are dying as a result."