Causes, incidence, and risk factors
Parkinson's disease was first described in England in 1817 by James Parkinson.
It happens when neurons (nerve cells) in a part of the brain called the substantia nigra gradually die, which leads to abnormally low levels of dopamine, and causes difficulty in controlling muscle tension and muscle movement. The disorder may affect one or both sides of the body, with varying degrees of loss of function. Some people also become severely depressed. Although early loss of mental capacities is uncommon, with severe Parkinson's the person may exhibit overall mental deterioration. Dementia can also be a side effect of some of the medications used to treat the disorder.

Internationally, Parkinson's disease affects about one to two in every 1000 persons, striking Europeans and North Americans more frequently than Asians or Africans and most often develops after age 50. It is also slightly more common in men than in women and is one of the most common neurologic disorders of the elderly.

Currently, research is being done on a test that may detect Parkinson's disease in its early stages, before it affects speech and movement.

Signs and Tests
Symptoms may be difficult to assess, particularly in the elderly. An examination may show "cogwheel" rigidity (the movements are jerky and stiff), tremors of the Parkinson's type, and difficulty initiating or completing voluntary movements. Reflexes are essentially normal.

Tests are not usually specific for Parkinson's, but they may be required to rule out other disorders that cause similar symptoms.

Treatment
There is currently no cure for Parkinson's disease, its symptoms can be treated with several different types of medication. The type of medication, the dose, and the amount of time between doses, or the combination of medications used may need to be adjusted as symptoms change. Many of the medications may cause severe side effects.

Deprenyl may be started early in the disorder to slow progression of symptoms and reduce the need for other medications. Amantadine and/or anticholinergic medications may be used to reduce early or mild tremors. Levodopa is a medication that the body converts to dopamine. It may be used to increase the body's supply of dopamine, which may improve movement and balance. Carbidopa is a medication that reduces the side effects of Levodopa and makes the Levodopa work better.

Additional medications to help reduce symptoms or control side effects of primary treatment medications include antihistamines, antidepressants, bromocriptine, monoamine oxidase inhibitors, and others.

Good general nutrition and health are important. Regular rest periods and avoidance of stress are recommended. Physical therapy, speech therapy, and occupational therapy may help promote functioning, positive attitude, and independence.

Experimental or less common treatments may be recommended. For example, surgery to destroy tissues responsible for tremors may reduce symptoms in some people. Transplantation of adrenal gland tissue (and fetal brain tissue) to the brain has been attempted, with variable results.