Parkinson's disease is a neurological disorder that affects a patient's ability to produce and control body movement. It is chronic (persisting over a long period of time) and progressive (worsens over time). Usually affecting older adults, Parkinson's can lead to severe disability for some people, but others may suffer only minor motor disorders.

In Parkinson's disease, a loss of neurons in the brain results in a reduction of the amount of dopamine, a chemical messenger that helps control muscle movement. Without dopamine, nerve cells cannot properly send messages.


Symptoms of Parkinson’s disease can be categorized as “motor” or “non-motor,” but the progression and type of symptoms can vary from person to person.

The more observable, motor (movement-related), symptoms include:

  • Tremor
  • Bradykinesia or slowed movements
  • Muscle stiffness or limb rigidity
  • Problems with balance and walking (gait)

It is common for only one side of the body to experience limitations with movement in the early stages of the disease.

Non-motor symptoms are not related to movement and may be harder to observe, yet they can severely impact individuals with Parkinson’s disease. These include:

  • Depression
  • Sleep disorders
  • Constipation or urinary problems
  • Cognitive impairment

A diagnosis of Parkinson’s disease can be made by a health care provider, but there are several symptoms that can be early warning signs. Having one of these symptoms is usually not a cause for worry, but if you or a loved one shows more than one sign, it’s time to see the doctor.

Stages of Parkinson’s Disease

While Parkinson’s disease can impact people in different ways and progress with varying levels of intensity, there are still typical patterns that the disease tends to follow when it comes to tracking movement-related symptoms. This progression is defined by the modified Hoehn and Yahr scale, ranging from zero to five, with zero representing no signs of Parkinson’s and five representing the most advanced stage of the disease.

In the first stage of the disease, mild symptoms may affect only one side or part of the body. Symptoms do not typically interfere with daily tasks.

In stage two, motor symptoms, such as tremor, start to affect both sides of the body, impairing movement in a more observable way. Daily activities become harder to complete independently.

In stage three, an individual’s pace of movement and balance may become affected. Movements become slowed, and maintaining balance becomes difficult, so living alone may be a challenge in this stage, though still possible.

During stage four of Parkinson’s disease, symptoms become more severe, so assistance is typically needed to complete daily activities and prevent falls. The individual should not live alone.

Stage five is the most debilitating stage of Parkinson’s, when the individual can no longer stand or walk and will require a wheelchair if not bedridden. Care should be provided at all times for the individual with advanced-stage Parkinson’s.

Young Onset Parkinson’s Disease

While most people with typical, or idiopathic (cause is unknown), Parkinson’s disease develop symptoms at ages 50 years or older, Young Onset Parkinson’s disease (YOPD) occurs in people younger than 50 years of age. Individuals with YOPD experience similar symptoms, but the progression of the disease occurs more slowly. Although YOPD is more likely to occur in individuals with a family history of Parkinson’s, not everyone with genes linked to Parkinson’s will develop the disease.


Parkinsonism refers to any condition that involves the types of movement changes seen in Parkinson's disease, such as tremors, slow movement, impaired speech, decrease in facial expressions, and muscle stiffness. These movements are caused by changes in or destruction of nerve cells that produce the chemical dopamine in a certain area of the brain.

Not all patients who have Parkinsonism have Parkinson's disease. Parkinsonian disorders may be caused by other conditions like:

  • Meningitis
  • Encephalitis
  • Progressive supranuclear palsy
  • Stroke
  • Caused by certain medications

Parkinson’s Research

The physician team is also at the forefront of research, currently focusing on disease pathogenesis and neuromodulation with the ultimate goal of identifying new medical and surgical interventions.

Dr. Saman Javedan on Houston Life

Learn how deep brain stimulation surgery can help patients with Parkinson’s disease.

Read the Full Story

Debra's Story: Deep Brain Stimulation

Watch how the team at Memorial Hermann Mischer Neuroscience uses deep brain stimulation (DBS) surgery to help reduce Debra’s symptoms of Parkinson's disease and improve her quality of life.

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