Medical illustration of diminished substantia nigra as seen in Parkinsons disease

In people with Parkinson's disease, specific groups of brain cells called neurons are slowly and progressively injured, then selectively degenerate or die.

This process causes the typical symptoms of Parkinson's disease, which doctors call "characteristic symptoms" because they are the major features of Parkinson's.

Characteristics of Parkinson's Disease

These are the characteristic symptoms of Parkinson's disease:

  • They tremble involuntarily.
  • They find their muscles become rigid and stiff, and they lose their ability to make rapid, spontaneous movements.
  • They walk in a recognizable manner, with a typical gait in which the body is bent or flexed.
  • They may have difficulty maintaining their balance.

The characteristic symptoms of moderate Parkinson's disease can be remembered with the acronym TRAP:

Tremor Involuntary trembling of the limbs
Rigidity Stiffness of the muscles
Akinesia Lack of movement or slowness in initiating and maintaining movement
Postural instability Characteristic bending or flexion of the body, associated with difficulty in balance and disturbances in gait

Early Signs and Symptoms of Parkinson's Disease

It is often difficult to pinpoint when a person with Parkinson's first began showing signs and symptoms of the disease. Many people vividly recall when they first noticed their tremor, but through close questioning, the physician often finds that subtle signs of the disease were present even before the tremor became noticeable.

The following table lists some of the early signs and symptoms of Parkinson's disease:

  • Change in facial expression (staring, lack of blinking)
  • Failure to swing one arm when walking
  • Flexion (stooped) posture
  • "Frozen" painful shoulder
  • Limping or dragging of one leg
  • Numbness, tingling, achiness or discomfort of the neck or limbs
  • Softness of the voice
  • Subjective sensation of internal trembling
  • Resting tremor

What Causes the Symptoms?

Medical illustration of dopamine agonists binding and activating dopamine receptors

Dopamine agonists are drugs that bind to and activate dopamine receptors.

The substantia nigra is a very small area located deep within the brain. The symptoms of Parkinson's disease do not become noticeable until about 80 percent of the cells of the substantia nigra have died.

Under the microscope we can see substantially fewer cells in this substantia nigra than in that of healthy brains, and the remaining cells often show signs of abnormality.

Once a specific neurotransmitter is produced that causes the substantia nigra to degenerate and die, dopamine is lost and dopamine-relayed messages to other motor centers cannot go through. This is this primary cause of the motor symptoms in Parkinson's disease.

Although we have some understanding that neurochemical disturbance causes the symptoms of Parkinson's, we still do not know what causes the neurodegeneration.

For more information about the University Physicians Consultation and Referral Service, please call 1-800-492-5538 (patients) or 1-800-373-4111 (physicians).

This page was last updated: June 13, 2013

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