Parkinson's disease is a slowly progressing disease of the nervous system that causes people to lose control over their muscles.
About 1 in 250 people over the age of 40, and about 1 in 100 people aged 65 or older, are affected by Parkinson's disease. Although the average age of onset is 57, Parkinson's occasionally appears in childhood. Men are more likely to develop Parkinson's than women.
Parkinson's is not a fatal condition. But the end stage of the disease can lead to pneumonia, choking, severe depression, and death.
Although the brain cells that control movement (the motor neurons) are located along the top of the brain, they rely on a chemical called dopamine that's manufactured in an area of the brain called the substantia nigra.
In Parkinson's, dopamine-producing cells in the substantia nigra are lost. In most cases, we don't know why. Primary Parkinsonism is the diagnosis in the majority of cases where the doctor doesn't know why these cells are dying. One thing researchers do know is that in the majority of people with Parkinson's disease, a protein called synuclein accumulates to form protein deposits called Lewy bodies. Researchers believe that Parkinson's disease is a late complication of protein accumulation, where the protein can accumulate in other areas of the brain, spinal cord, peripheral nerves, and in the intestinal tract.
Secondary Parkinsonism is due to some disease (e.g., nervous system conditions, heart disease, brain tumors, viruses) or chemical interfering with or damaging dopamine-producing cells in the brainstem. The most common cause is side effects of medication for other problems. Medications that can cause secondary Parkinsonism include:
- haloperidol* and other medications used to treat hallucinations
- metoclopramide (an antinausea medication)
Less common causes of secondary Parkinsonism include poisoning by carbon monoxide or manganese (a type of mineral), lesions and tumors in the brainstem, and a rare illicit drug called N-MPTP. An outbreak between 1918 and 1924 of a disease called von Economo's encephalitis left thousands of people across North America with Parkinson's.
A number of genetic mutations have recently been identified, suggesting that Parkinson's may run in some families. But a major US twin study suggested that environment plays a larger role than inheritance. The current consensus is that genetic factors are dominant only in Parkinson's that appears before age 50.