Researchers have found a drug used to treat diabetes protects the brain of patients with a rare and fatal disease closely associated with Parkinson's.

A drug used to treat diabetes has the potential to help sufferers of a rare and devastating Parkinson's-like degenerative brain disease.

A study published in medical journal Brain found neurons in the brains of patients with multiple system atrophy (MSA) showed insulin resistance, which is also marker of diabetes.

Scientists, led by Dr Fares Bassil from the University of Pennsylvania, then used the diabetes drug Exendin 4 on mice with MSA.

The drug improved insulin resistance in the brains of the mice and importantly preserved some of the neurons normally damaged by the disease.

This is an "incredibly encouraging" discovery, says Australian Professor Bryce Vissel, Director Neuroscience and Regenerative Medicine in the Faculty of Science at UTS.

"If proven to be effective for MSA, even if it slows it just a little bit, it wouldn't have to go through enormous amounts of safety testing and development before it gets used for this disease," Prof Vissel said.

MSA is a rare progressive brain disease that affects adults, usually in their 50s or 60s.

It is caused by degeneration, or atrophy, of nerve cells in specific areas of the brain.

The average survival time from diagnosis is six-to-nine years and there are no effective therapies to treat the symptoms which include fainting spells, loss of muscle co-ordination and speech difficulties.

"The suggestion that this diabetes drug could offer a therapeutic approach for MSA is therefore potentially of enormous importance and deserves close scrutiny," said Prof Vissell.

While there is still a lot of work to do in the form of clinical human trials, Prof Vissell says, Exendin 4 may also offer "promise" for the treatment of Alzhiemer's disease.

"Numerous studies have identified Type 2 diabetes as a risk factor for stroke, Alzheimer's disease, vascular dementia, and Parkinson's disease, among other disorders," he said.

"We have previously suggested that brain insulin resistance, which is a characteristic of Type 2 diabetes, follows from the inflammation that is a hallmark of neurological diseases."