Parkinson's disease, also known as Parkinson disease, PD, paralysis agitans, and shaking palsy is a gradually progressive, degenerative neurologic disorder which typically impairs the patient's motor skills, speech, writing, as well as some other functions. Sufferers often have a fixed, inexpressive face, tremor at rest, slowing of voluntary movements (bradykinesia), an unusual posture, and muscle weakness. In extreme cases there is a loss of physical movement (akinesia).

Parkinson's disease is both chronic and progressive. Chronic means long-term, while progressive means it gradually gets worse.

Parkinsonism is a neurological syndrome characterized by tremor, rigidity, postural instability, and hypokinesia (decreased bodily movement). A syndrome is the association of several clinically recognizable features, signs, symptoms, phenomena or characteristics that often occur together. Parkinson's disease is the most common cause of Parkinsonism. Put simply - Parkinsonism includes the signs and symptoms that resemble Parkinson's disease.

While about 5% of individuals with Parkinson's disease are under the age of 40 years, the majority are over 50. When signs and symptoms develop in an individual aged between 21 and 40 years, it is known as Young-onset Parkinson's disease. Approximately 1 in every 20 patients diagnosed with PD is under 40 years of age. When signs and symptoms appear in people under 18 years of age, it is known as Juvenile Parkinson's disease. It affects both sexes; males slightly more than females.

According to the National Institutes of Health (NIH), USA, approximately 500,000 Americans are affected by Parkinson's disease; about 50,000 new diagnoses are made each year. The National Health Service (NHS), UK, estimates that about 120,000 people in the United Kingdom are affected.

As a significant number of elderly patient with early Parkinson's disease symptoms assume that their symptoms may form part of normal aging and do not seek medical help, obtaining accurate statistics is probably impossible. There are also a several different conditions which sometimes have comparable signs and symptoms to PD.

PD is named after James Parkinson (1755-1824), an English apothecary surgeon, paleontologist, geologist and political activist. In his most famous work An Essay on the Shaking Palsy (1817), he was the first person to describe paralysis agitans, which eventually was named after him.

Parkinson's disease belongs to a group of conditions called movement disorders. Movement disorders describe a variety of abnormal body movements that have a neurological basis, and include such conditions as cerebral palsy, ataxia, and Tourette syndrome. Parkinson's disease results from decreased stimulation of the motor cortex by the basal ganglia, typically caused by insufficient formation and action of dopamine.

There is no current cure for Parkinson's disease (April, 2010). Treatment focuses on alleviating symptoms. Sometimes treatment may include surgery.

According to Medilexicon's medical dictionary:
Parkinsonism is: