A new study suggests that positron emission tomography (PET) scans of the heart can help identify people at risk for Parkinson’s disease or Lewy body dementia up to seven years before they develop symptoms.

According to Parkinson's News Today, the National Institutes of Health (NIH) study found that the loss of norepinephrine in the heart preceded a loss of dopamine in the brain and the onset of Parkinson’s symptoms or those caused by Lewy body dementia. The second most common type of dementia, after Alzheimer’s, Lewy body dementia affects brain regions involved in thinking, memory and movement. Norepinephrine is a signaling molecule derived from dopamine, the chemical messenger that is lost in Parkinson’s and Lewy body patients.

Symptoms of these disorders occur after there’s been considerable damage to the brain’s dopamine-producing neurons. If doctors can diagnose Parkinson’s before symptoms are evident, they may help to intervene by suggesting lifestyle changes or medications when it’s early enough to make a difference.

“Once symptoms begin, most of the damage has already been done,” said Dr. David Goldstein, principal investigator of the study at the National Institute of Neurological Disorders and Stroke. “You want to be able to detect the disease early on.”

The study was published in the Journal of Clinical Investigation. The researchers found that PET scans were highly effective identifying patients who were at risk of developing Lewy body dementia or Parkinson’s disease by measuring levels of 18F-dopamine radioactivity.

Goldstein said that people with Lewy body diseases, including Parkinson’s, have a severe lack of cardiac norepinephrine, which is normally stored and released by nerves that supply the heart. His team used the 18F-dopamine PET tracer to measure the levels of norepinephrine in the heart, to determine if it could identify people who could develop Parkinson’s or Lewy body dementia later.

The PET scans were administered to 34 people every 18 months for 7.5 years or until disease diagnosis. All the participants had at least three risk factors for Parkinson’s disease that included family history, loss of smell, a common Parkinson’s nonmotor symptom, or dream enactment in which people act out their dreams — a condition that can precede the disease. Symptoms also included low blood pressure or orthostatic intolerance where people become light-headed upon standing.

Eight out of nine people with initial low levels of 18F-dopamine went on to develop the disease along with one of the participants who had normal readings. The researchers noted that person’s levels were low at diagnosis.

Of these nine people, 26% of the total study group, six developed Parkinson’s, two developed Lewy body dementia, and one developed Parkinson’s with dementia. This is a “larger percentage that would be expected in the general population,” the researchers said.

“The loss of norepinephrine in the heart predicts and precedes the loss of dopamine in the brain in Lewy body diseases,” said Goldstein, according to Parkinson’s News Today. “If you could salvage the dopamine terminals that are sick but not yet dead, then you might be able to prolong the time before the person shows symptoms.”