- Parkinson’s disease, a neurodegenerative condition, is characterized by depletion of the neurotransmitter dopamine in the brain.
- The condition can be diagnosed only once symptoms such as shaking, stiffness and problems with balance and coordination start, by which time the nervous system has been damaged.
- New research suggests that changes in the heart precede the symptomatic stage of the disease.
- Using PET scans, researchers found that low levels of dopamine in the heart were strong predictors of later development of Parkinson’s disease or dementia with Lewy bodies.
- The findings may lead to ways of diagnosing the conditions before damage has begun.
Parkinson’s disease affects at least 1 million people in the United States and 10 million worldwide. It is the second most common neurodegenerative disease after Alzheimer’s disease, and often leads to another form of dementia, dementia with Lewy bodies, also known as Lewy body dementia.
In people with Parkinson’s disease, symptoms such as tremor, slowness of movement, limb stiffness and balance problems result from a lack of the neurotransmitter dopamine.
A second neurotransmitter, norepinephrine (noradrenaline), also decreases in Parkinson’s disease, affecting the functions of the sympathetic nervous system.
This can lead to fatigue, irregular blood pressure, decreased movement of food through the digestive tract, and sudden drops in blood pressure on standing.
Once the symptoms are evident, substantial damage to the nervous system will have happened, so researchers are looking for ways to identify those at greatest risk, and to diagnose the disorders before much damage occurs.
Can heart scans tell a story about Parkinson’s?
One potential avenue is looking for changes that happen earlier in other parts of the body. New research using positron emission tomography (PET) scans of the heart has found that at-risk individuals with low 18F-dopamine-derived radioactivity — a cardiac imaging agent — in the heart were highly likely to develop Parkinson’s disease or dementia with Lewy bodies during long-term follow-up.
The study, by researchers at the National Institutes of Health (NIH), is published in The Journal of Clinical Investigation.
Dr. Christopher Tarolli, associate professor of neurology at the University of Rochester Medical Center, not involved in the research, explained the set-up of the study to Medical News Today.
“The study followed a relatively small group of individuals at high risk for the development of Parkinson disease or dementia with Lewy bodies, but followed these individuals for a number of years to assess whether the use of cardiac PET could be used as a predictor of conversion to a clinical diagnosis of [Parkinson’s disease] or [dementia with Lewy bodies],” he said.
According to Dr. Tarolli, “[t]he results were quite compelling, with individuals with abnormal 18F dopamine cardiac PET at baseline significantly more likely to be diagnosed with [Parkinson’s disease] or [dementia with Lewy bodies] over the following 7.5 years, compared to those with normal scans.”
The researchers suggest that this could be a method of determining which people with risk factors for Parkinson’s disease and Lewy body dementia are most likely to go on to develop one of these conditions.
PET holds early diagnosis potential
Dr. Michael S. Okun, director of the Norman Fixel Institute for Neurological Diseases at the University of Florida Health, and medical advisor at Parkinson’s Foundation, not involved in this research, explained that:
“If a biomarker using cardiac noradrenergic deficiency can be shown to identify a disease process that will eventually progress to dementia with Lewy Bodies this could be really useful for future clinical trials in this population.”
In this study, the researchers investigated levels of dopamine in the hearts of 34 people with three or more risk factors for Parkinson’s disease or dementia with Lewy bodies. All participants underwent cardiac 18F-dopamine PET scans every 18 months for a total of 7.5 years. A number of participants dropped out before the end of the study.
At-risk individuals whose scans showed low 18F-dopamine-derived radioactivity in the heart were much more likely to develop Parkinson’s disease or dementia with Lewy bodies during long-term follow-up.
Of the 20 participants who completed the study, nine had low 18F-dopamine-derived radioactivity in the early scans.
Of these, eight later received a diagnosis of Parkinson’s disease or dementia with Lewy bodies, whereas only one of 11 people with normal levels was subsequently diagnosed. All those who developed dementia with Lewy bodies had low radioactivity in early scans or at diagnosis.
Dr. Tarolli told MNT: “The results were quite compelling, with individuals with abnormal 18F dopamine cardiac PET at baseline significantly more likely to be diagnosed with [Parkinson’s disease] or dementia with Lewy bodies over the following 7.5 years, compared to those with normal scans.”
“These findings are notable, as they suggest 18F dopamine cardiac PET may be a reliable clinical biomarker for the identification of individuals who will develop these conditions, at least among those who are at elevated risk,” he added.
Dr. Okun agreed:
“An interesting finding in a small number of individuals was that when multiple [Parkinson’s disease] risk factors were present, a low cardiac 18F-dopamine derived radioactivity predicted the subsequent diagnosis dementia with Lewy bodies. Also interesting was that in the United States this cardiac test is not commonly applied in Parkinson’s and related populations and thus could represent a missed opportunity.”
Clinical use remains some way off
Dr. Tarolli said there were barriers to overcome before these types of scans might be used for clinical diagnosis of Parkinson’s disease and dementia with Lewy bodies.
“The first is the availability of the scan itself, which is currently only available on a research basis at a very small number of locations. Beyond this, questions remain about how to identify the correct patients to screen with scanning,” he told us.
“As we consider how we might utilize the scan to screen for individuals at the increased risk, it would be important to know whether these results hold only in this group at increased risk of developing [Parkinson’s disease] for other reasons, or whether the high predictability of an abnormal scan remains among a more general population,” he further commented.
He did, however, suggest that the findings might impact clinical research: “Currently, we don’t have any medications that can modify the course of these diseases, so earlier identification with 18F dopamine cardiac PET, as described in this study, may not have an immediate impact on clinical care today.”
“However, where this could be highly impactful is in clinical research — identifying individuals with ‘prodromal Parkinson disease’ years before their clinical diagnosis might allow us to assess therapeutics much earlier in the disease process, and increase the likelihood of us having an impact on disease trajectory,” Dr. Tarolli emphasized.
Early days, then, but this study identifies another potential biomarker for diagnosing neurodegenerative disease before the effects become life-altering.
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