Facts about PD
An estimated one million people in the United States and over five million worldwide are living with Parkinson’s disease.
- PD affects 1 in 100 people over the age of 60. In the US, 60,000 new cases will be diagnosed this year alone.
- Average age of onset is 60. Some people are diagnosed under the age of 40.
- Non-movement related symptoms include sleep and digestion problems, cognitive dysfunction, and mood disorders such as depression and apathy.
- There is no known cure for Parkinson’s disease. Current treatments can only mask some symptoms.
Parkinson’s disease is a chronic, degenerative neurological disorder. There is no objective test, or biomarker, for Parkinson’s so the rate of misdiagnosis can be relatively high, especially when the diagnosis is made by a non-specialist. Therefore, estimates of the number of people living with the disease vary.
Parkinson’s disease was first characterized extensively by an English doctor, James Parkinson, in 1817. Today, we understand Parkinson’s to be a disorder of the central nervous system that results from the loss of cells in various parts of the brain, including a region called the substantia nigra. The substantia nigra cells produce dopamine, a chemical messenger responsible for transmitting signals within the brain that allow for coordination of movement. Loss of dopamine causes neurons to fire without normal control, leaving patients less able to direct or control their movement. PD is one of several diseases categorized by clinicians as a movement disorder.
What are the symptoms of Parkinson’s disease?
People are generally most familiar with the motor symptoms of PD, as they are the most evident signs of the disease to an observer. These symptoms, also called the “cardinal” symptoms, are resting tremor, slowness of movement (bradykinesia), postural instability (balance problems) and rigidity. Some other physical symptoms, such as gait problems and reduced facial expression, are also of note. These are due to the same lack of coordination of movement that causes the better-known symptoms of tremor and slowness.
There is also increasing recognition of the importance of other symptoms of PD, referred to as “non-motor” or “dopamine-non-responsive” symptoms. While neither of these terms are entirely inclusive, these symptoms are quite common and can have a major impact on the lives of people with PD. For example, cognitive impairment occurs frequently and can,range from mild memory difficulties to dementia, and also can include mood disorders, such as depression and anxiety. Also common are sleep difficulties, loss of sense of smell, constipation, speech and swallowing problems, unexplained pains, drooling, constipation and low blood pressure when standing.
Parkinson’s symptoms manifest differently in different patients. Many patients experience some symptoms and not others, and even the pace at which the disease progresses varies from individual to individual.
How is Parkinson’s disease diagnosed?
The cardinal symptoms of Parkinson’s (resting tremor, slowness of movement (bradykinesia), balance problems (postural instability) and rigidity are the hallmarks of the disease. These symptoms, which often appear gradually yet with increasing severity, are usually what first bring patients to a neurologist for help. Typically, symptoms begin on one side of the body and migrate to the other side over time.
Currently, there is no test (such as a blood test, brain scan or EEG) to make a diagnosis of PD. Instead, diagnosis is made by a doctor taking a careful medical history and performing a thorough neurological examination. Physicians look for two or more of the cardinal signs of PD to be present to make a diagnosis. Frequently, the doctor will also look for responsiveness to Parkinson’s medications as further evidence that PD is the correct diagnosis.
Because there is no definitive test for PD and because Parkinson’s symptoms are similar to those of other neurological conditions, the misdiagnosis rate of PD is significant. It is worthwhile for patients who are diagnosed to consider a second opinion and to reach out to a neurologist with specific expertise in movement disorders.
What causes Parkinson’s disease?
The exact cause of Parkinson’s disease is unknown, although research points to a combination of genetic and environmental factors. If a continuum existed with exclusively genetic causes at one end and exclusively environmental causes at the other, different patients would likely fall at many different places along that continuum.
In the past 10 years, researchers have identified a number of rare instances where Parkinson’s disease appears to be caused by a single genetic mutation. In these cases, the mutated gene is passed from generation to generation, resulting in many Parkinson’s cases within an extended family. On the opposite of end of the continuum is a group of heroin users in California in the early 1980s who took drugs contaminated with a substance called MPTP. After ingesting this chemical, the drug users were stricken with a form of PD that was primarily, if not exclusively, “environmental” in origin.
For most Parkinson’s patients, the cause lies somewhere in the middle. While many patients report one or more family members with the disease, it is not always clear that one or several genes are the cause. Similarly, while some patients suspect that exposure to one or another chemical or environmental toxin caused their PD, this also cannot be proven conclusively. Scientists currently believe that genetic and environmental factors interact to cause PD in the majority of cases. Research into this subject continues aggressively every day, however it is generally impossible to determine what specifically caused an individual’s PD.