Parkinson's disease may be one of the most baffling and complex of the neurological disorders. Its cause remains a mystery but research in this area is active, with new and intriguing findings constantly being reported.

Parkinson's disease was first described in 1817 by James Parkinson, a British physician who published a paper on what he called "the shaking palsy." In this paper, he set forth the major symptoms of the disease that would later bear his name.

Parkinson's disease belongs to a group of conditions called motor system disorders. The four primary symptoms are tremor or trembling in hands, arms, legs, jaw, and face; rigidity or stiffness of the limbs and trunk; bradykinesia or slowness of movement; and postural instability or impaired balance and coordination. As these symptoms become more pronounced, patients may have difficulty walking, talking, or completing other simple tasks.

The disease is both chronic, meaning it persists over a long period of time, and progressive, meaning its symptoms grow worse over time. It is not contagious nor is it usually inherited — that is, it does not pass directly from one family member or generation to the next.

Parkinson's disease is the most common form of parkinsonism, the name for a group of disorders with similar features These disorders share the four primary symptoms described above, and all are the result of the loss of dopamine-producing brain cells. Parkinson's disease is also called primary parkinsonism or idiopathic Parkinson's disease; idiopathic is a term describing a disorder for which no cause has yet been found. In the other forms of parkinsonism either the cause is known or suspected or the disorder occurs as a secondary effect of another, primary neurological disorder.