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What is Parkinson's Disease?

By Jennifer Markowitz, MD ; Updated August 14, 2017

Parkinson’s disease is a progressive disorder of the nervous system that affects movement and other major functions like thinking and sleep. According to the February 2013 American Family Physician, about 1 percent of Americans over age 60 and up to 4 percent over age 80 have Parkinson’s disease. The classic movement symptoms of Parkinson’s disease include tremor, or shaking; slowed movement; rigidity, or muscle stiffness; and postural instability, or poor balance. Although symptoms can respond to treatment with medication or surgery, the disease worsens over time, and no cure is currently available.

Changes in the Brain

For reasons that aren’t understood, people with Parkinson’s disease progressively lose cells in multiple specific areas of the brain. The movement symptoms are related to loss of brain cells in an area called the substantia nigra, which makes the chemical messenger dopamine. Loss of brain cells that make other chemical signals, such as serotonin and norepinephrine, can lead to the other, non-movement symptoms of the disease.

Movement Symptoms

The symptoms of Parkinson’s disease can vary between people. They are often worse on one side of the body. Tremor, or shaking, can affect the limbs or face and occurs at rest. Slowed movement, known as bradykinesia, results in decreased facial expression and overall fewer spontaneous movements. Bradykinesia makes it hard to perform everyday activities like buttoning clothes and results in a slow, shuffling walk. Muscle stiffness, or rigidity, can cause pain, as muscles of the neck, trunk and limbs don’t relax normally when they’re not being used. Postural instability refers to a problem with balance that may cause a person to fall backward easily. Other symptoms can include “freezing,” or stopping just as one is about to take a step forward, and dystonia — an involuntary (and often painful) contraction of muscles.

Non-Movement Symptoms

People with Parkinson’s disease suffer from a host of non-movement problems that greatly affect their quality of life. According to the February 2013 American Family Physician, 60 percent of people with Parkinson’s disease develop dementia — a severe disorder of memory, personality and thinking — within 12 years of diagnosis. Other symptoms can include hallucinations (seeing things that aren’t there), fatigue, trouble sleeping, pain, urinary and sexual problems, low blood pressure upon standing, swallowing problems and drooling. Some symptoms may start years before the movement symptoms occur — for instance, decreased sense of smell, constipation, depression and REM sleep behavior disorder, in which a person acts out vivid or scary dreams.


One of the defining features of Parkinson’s disease is improvement of symptoms after taking carbidopa-levodopa (Sinemet, Parcopa). Carbidopa-levodopa is converted to dopamine in the brain, helping to replace some of the dopamine that has been lost. Slowed movement, rigidity and tremor can improve with carbidopa-levodopa, but balance problems respond less well. Treatment is generally started when symptoms interfere with a person’s ability to function. Other types of drugs are available which help the brain use and respond to dopamine more effectively. But over time, medication works less well and people experience “off” periods — an abrupt return of their symptoms. They may also experience dyskinesias — abnormal involuntary movements — triggered by the medications. For some people in this situation, surgery to implant “deep brain stimulators” can offer relief. Other approaches, like physical and speech therapy, may be helpful. Eventually, symptoms progress in all people with Parkinson’s disease, leading to increased risk of death.

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