Parkinson’s disease, a common movement disorder known for tremors and balance problems, affects around 1 million people in the U.S., with nearly 90,000 new cases each year. Over the next two decades, diagnoses are estimated to surge: By 2050, 25.5 million people worldwide will be living with Parkinson’s disease, a 112% increase from 2021, according to a new journal study.

While scientists have identified certain risk factors associated with Parkinson’s, the exact cause is unknown. “Every year Parkinson’s disease incidence is going up,” says Dr. Miran Salgado, a neurologist at NewYork-Presbyterian Brooklyn Methodist Hospital. “We know there is some connection to genetics and environmental toxins. Another key risk factor is age. This is an older people’s illness.”

Parkinson’s disease causes nerve cells in the brain to deteriorate over time, and there is no cure. Some patients advance more rapidly than others. “My take-home message is no two people with Parkinson’s progress at the same rate, so don’t worry about the clinical stage so much and focus on the mental and physical functions,” says Dr. Salgado. “It’s also important to have hope because there are many tools we have now in our toolbox to make your life better and manage your symptoms over a long period.”

Health Matters spoke with Dr. Salgado, who shared information on signs and symptoms of the condition, causes, risk factors, and how it is diagnosed and treated.

What is Parkinson’s disease?

Dr. Salgado: Parkinson’s disease affects the central nervous system, and it is a constellation of many symptoms put together. Movement problems are the core symptoms of the disease, but we have since realized there are different manifestations and variations of Parkinson’s.

The name dates to 1817, when James Parkinson, a revolutionary family practitioner in England wrote about six patients who had slowed motor movements, tremor, a bent posture, and they took quick, short steps. However, their mind was preserved.

How does Parkinson’s disease affect the brain?

In patients with Parkinson’s, a protein in the brain (called alpha-synuclein) becomes abnormal, mutates, and infects the brain cells that produce dopamine. Dopamine is a neurotransmitter that controls our motor system, as well as mood and behavior. As the brain cells deteriorate and die, the body produces less dopamine, and that leads to the motor-related symptoms that we see in Parkinson’s disease.

Is there a known cause for Parkinson’s disease?

Most cases of Parkinson’s are idiopathic, meaning that they occur with no known cause. Some cases seem to be genetic. The number of known genetic cases has gone up from approximately 5% about 20 years ago to say 10% to 15% now, because we are finding more and more kinds of gene defects which give rise to this Parkinson’s disease. 

Environmental factors may also play a role together with genetics. We know that Parkinson’s disease is more common in rural areas where well water was used, so it might be toxins like pesticides or insecticides getting into the drinking water. There are also toxins people are exposed to in factories — solvents or fumigants — that have also been implicated as causing disruptions of nerve cells that give rise to Parkinson’s disease.

There is also new research suggesting that Parkinson’s may spread from the gut, ascend to the brainstem and across the brain or the olfactory system. 

What are the symptoms of Parkinson’s disease?

The four cardinal features are related to movement and usually start on one side of the body:

• Slowness
• Tremor
• Stiffness
• Difficulty balancing

There are other manifestations that may appear earlier and before movement-related disorders. They are important because they may help us detect the disease early and develop therapy to slow the progression. These symptoms, known as prodromal, include:

• Loss of smell
• Severe constipation
• Bladder and sexual dysfunction
• Depression
• REM sleep disorder

Who is most at risk?

Anyone can develop Parkinson’s disease, but studies show that the condition affects more men than women. Parkinson’s tends to affect people after age 60, but around 10% will have early-onset Parkinson’s (before age 50). Although not always, cases earlier in life may be inherited or linked to gene alterations.

How is Parkinson’s disease diagnosed?

Diagnosing Parkinson’s disease consists of:

• Evaluating a person’s medical history.
• Conducting neurological examinations that assess movement, sensation, hearing and speech, vision, coordination and balance.
• Testing for known genetic mutations in instances where Parkinson’s disease may have been inherited.
• Imaging, to see abnormalities in the brain. One type of SPECT (single-photon emission computed tomography) is a dopamine active transporter (DaT) scan that enables doctors to see if there is a significant decrease in dopamine. The Fluorodopa PET scan, more recently made available, is considered more sensitive than the DaT scan to detect dopamine cell loss.
  It is important to note that abnormal results can also be due to other Parkinsonian syndromes with additional clinical features, including progressive supranuclear palsy (PSP); multiple systems atrophy (MSA); cortical-basal degeneration (CBD); and Lewy body dementia.

Studies have also shown that a laboratory test called the alpha-synuclein seeding amplification assay was able to identify Parkinson’s in people with the disease, as well as in those at high risk for developing it, even if they were not yet showing symptoms. The test requires the collection of spinal fluid or biopsies of the skin, colon, or salivary glands. It can detect the protein alpha-synuclein with high accuracy, which could help doctors begin treatment much earlier.

How is Parkinson’s treated?

Unfortunately, we do not have therapies to slow the progression of Parkinson’s disease, and there is no cure. What we offer today is improving quality of life. There is a fair amount of evidence showing that moderate to high intensity exercises can help with managing the disease.  

The medication commonly prescribed is called levodopa. Nerve cells use levodopa to make dopamine to replenish the brain’s dwindling supply.

Other medications include dopamine agonists that work to stimulate the production of dopamine in the brain, and amantadine, used to treat the involuntary movements seen later with Parkinson’s. Enzyme inhibitors, such as MAO-B inhibitors, are also available. They increase the amount of dopamine by slowing down enzymes that breakdown dopamine in the brain.

What are the surgical treatment options?

There are surgical therapies like deep brain stimulation. We do this when Parkinson’s is advanced to control symptoms. There is also focused ultrasound, which was approved by the Food and Drug Administration to treat Parkinson’s symptoms in 2021. Focused ultrasound uses ultrasound beams to make lesions in brain structures to control movements and improve function.

Are there new treatments for Parkinson’s on the horizon?

Gene therapy trials are about to begin at NewYork-Presbyterian under Dr. Michael Kaplitt. Monoclonal antibodies targeting alpha-synuclein are still being pursued. Also some diabetes drugs, such as GLP-1 antagonists, have shown promise in slowing disease progression.

Miran Salgado, M.D., is a board-certified neurologist at NewYork-Presbyterian Brooklyn Methodist Hospital, where he is a movement disorder specialist and chief of neurology. He works with the Weill Cornell Medicine brain and spine team providing care for patients with Parkinson’s disease, movement disorders, stroke, and other neurological conditions.