New Study Says Parkinson’s May Actually Be 2 Diseases

A surprising new study has hypothesized that Parkinson’s disease is actually two different diseases: one that starts in the brain and one that starts in the intestines. That can help explain why Parkinson’s patients have a range of symptoms, the study’s researchers argue.

The study, which was published in the journal Brain, used positron emission tomography (PET) and magnetic resonance imaging (MRI) imaging techniques to analyze 37 people who were either already diagnosed with Parkinson's disease or had a high risk of developing the disease.

The scans discovered that some people had damage to their brain's dopamine system before suffering damage to their heart and intestines. But other patients had damage to the nervous systems in their intestines and heart before damage was visible in their brain's dopamine system.

“These findings support the existence of brain-first and body-first subtypes of Parkinson’s disease,” the authors concluded in the study.

Parkinson’s Disease Basics

Parkinson’s disease is a brain disorder that causes shaking, stiffness, and difficulty with walking, balance, and coordination, according to the National Institute on Aging (NIA).

Symptoms of Parkinson’s disease usually start gradually and get worse over time. As the disease progresses, patients may develop trouble walking and talking, along with mental and behavioral changes, sleep problems, depression, memory difficulties, and fatigue, the NIA says.

About 60,000 new cases of Parkinson’s disease are diagnosed each year, according to the National Institutes of Health (NIH).

One major risk factor for Parkinson’s disease is age, with most people who have the disease developing it at around age 60.

Parkinson’s disease usually has four main symptoms:

• Trembling in hands, arms, legs, jaw, or head
• Stiffness of the limbs and trunk
• Slowness of movement
• Impaired balance and coordination

Patients may also experience depression and other emotional changes, difficulty swallowing, chewing, and speaking, urinary problems or constipation, skin issues, and trouble sleeping, the NIA says.

Why 2 Types of Parkinson’s Disease Are Plausible

Study coauthor Per Borghammer, MD, PhD, a professor of clinical medicine at Aarhus University, tells Verywell that it’s unclear why this might happen, and points out that this is a hypothesis at this point. However, he and his research team have some theories.

One theory is that the type of Parkinson’s that starts in the intestines is triggered by the gut microbiome, as well as inflammatory states and infections. “In addition, the person probably needs to be vulnerable, [and] have some risk genes,” Borghammer says. That can include being older, which is a known risk factor for Parkinson’s disease, he says.

When it comes to “brain-first” Parkinson’s disease, Borghammer thinks the onset is also probably triggered by certain genes, along with aging.

With both types of Parkinson’s disease, the disease process likely starts with bad luck, Borghammer says. “In short, the first pathology is simply a random event and, if the person is vulnerable, the pathological process may multiply and spread out of control,” he says. Borghammer compares this to the way cancer develops. “The first cancer cell is most likely created by random events—random mutations—but then it multiplies and spreads,” he says.

“Parkinson’s disease is a neurodegenerative disorder. It is not surprising that a degenerative disorder would involve multiple systems within the brain,” Amit Sachdev, MD, medical director in the division of neuromuscular medicine at Michigan State University, tells Verywell. Sachdev did not work on the new study.

“It makes sense that a patient might have several systems become involved at once and that those systems might look like they do very different thing," he says. "In the end, while the exact order with which the disease affects people might be very person specific, the involved systems are a part of a predictable disease syndrome.”

Symptoms Differ Among Patients

There is variation in symptoms from patient to patient but, in general, Borghammer says that the following may be true of the progression of symptoms in people with each type of Parkinson’s disease.

In patients where Parkinson’s disease starts in the gut:

“[They] first develop constipation, blood pressure problems, and urinary problems, because the autonomic nervous system is the first to be damaged,” Borghammer says. “The pathology spreads to the bottom of the brainstem and then the sleep disorder emerges. Only years later, the motor symptoms emerge.”

In patients where Parkinson’s disease starts in the brain:

The order of symptoms will be opposite patients whose Parkinson’s disease starts in the gut, Borghammer says. “The pathology probably starts inside the brain and doesn't really create a lot of symptoms initially,” he says. “The first clear symptom to emerge is the motor symptoms, signifying that the dopamine system is damaged.”

The disease then spreads down in the brainstem, where it can cause sleep issues, he says. “Finally, the pathology reaches the peripheral nervous system and causes constipation, urinary problems, and blood pressure problems.”

How This Could Impact Treatment

If some forms of Parkinson’s disease start in the gut, “we may be able to prevent the disease altogether by removing these risk factors, or lower the risk of Parkinson’s disease by making sure that we have a good microbiome in our guts,” Borghammer says. “Also, it is theoretically possible that the symptoms of Parkinson’s disease patients can be directly treated by manipulating the microbiome.”

People who have Parkinson’s disease that starts in the gut may be able to be identified earlier, which may help slow the progression of the disease, Borghammer says.

“A better understanding of how degeneration involves different body regions might help us diagnose the disease earlier,” Sachdev says. “Early intervention is best when trying to manage a degenerative disorder.”

While Borghammer acknowledges that the notion of Parkinson’s disease as two separate conditions is a theory at this point, he says hopes that it will inspire other researchers to explore the concept more.

“Different genes or other factors may cause one type or the other,” he says. “If we can identify such factors, we can perhaps develop new treatments to alter the cause of the disease and even prevent it altogether. But a lot of research still has to be done before we get there.”