Australian researchers say they have made a significant breakthrough in identifying the cause of delirium, a brain-related condition which affects up to 50 per cent of elderly hospital patients.

Key points: Delirium is a brain syndrome common in elderly hospitalised patients

Delirium is a brain syndrome common in elderly hospitalised patients Patients suffer confusion, agitation and hallucinations

Patients suffer confusion, agitation and hallucinations Researchers say it's caused by abnormal glucose metabolism in the brain

Associate Professor Gideon Caplan from the Prince of Wales Hospital in Randwick, NSW, said by using PET scans his team identified abnormal glucose metabolism in the brain as the leading cause of delirium.

"In 10 years of delirium research at Prince of Wales, we have found the answer to a 2,500-year-old mystery — what is happening in the brain during delirium," he said.

"This breakthrough now informs us as to where to aim our therapeutic interventions to treat, and hopefully to beat delirium."

As many as one in 10 patients in hospital have delirium, a condition where patients become restless, suffer illusions and become incoherent.

One in four patients aged over 65 will be diagnosed with delirium, and often it is missed by hospital staff.

Using PET scans, researchers found changes in the part of the brain governing memory, and executive function.

Researchers found when the brain was unable to metabolise glucose efficiently, brain function deteriorated, causing delirium.

Associate Professor Caplan said the findings were extremely important.

"This condition is so common, and there is no treatment or way to prevent delirium," he said.

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Possible treatments on the horizon

The good news is there are already treatments which increase glucose uptake in the brain, such as insulin, which is used to treat diabetes.

Doctors at Prince of Wales Hospital plan to trial insulin delivered in an inhaler, via the nose, which means it will go directly to the brain.

It would be given to elderly patients at risk of delirium.

Associate Professor Caplan said preventing and treating delirium was important, as it is precursor to dementia.

"Delirium accelerates the progression of dementia, so if we could treat delirium, we could potential prevent dementia in some patients," he said.