Parkinson’s disease is a chronic, degenerative neurological disorder that affects one in 100 people over age 60. While the average age at onset is 60, some people are diagnosed at 40 or younger. There is no objective test, or biomarker, for Parkinson’s disease, so the rate of misdiagnosis can be relatively high, especially when the diagnosis is made by a non-specialist. Estimates of the number of people living with the disease therefore vary, but recent research indicates that at least one million people in the United States, and more than five million worldwide, have Parkinson’s disease.
Parkinson’s disease was first characterized extensively by an English doctor, James Parkinson, in 1817. Today, we understand Parkinson’s disease 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. Parkinson’s disease is one of several diseases categorized by clinicians as movement disorders.
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 Parkinson’s 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 a great number of Parkinson’s disease cases within an extended family. On the opposite end of the continuum, in the early 1980s, a group of heroin users in California took drugs from a batch contaminated with a substance called MPTP. After ingesting this chemical, the drug users were stricken with a form of Parkinson’s disease that was primarily, if not exclusively, “environmental” in origin.
For most Parkinson’s patients, the cause lies somewhere in the middle. While many Parkinson’s 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 Parkinson’s disease, this also cannot be conclusively proved. Scientists currently believe that in the majority of cases, genetic and environmental factors interact to cause Parkinson’s disease. Research into this subject continues aggressively every day. Unfortunately, however, it is generally impossible to determine what specifically caused an individual’s Parkinson’s disease.
What Are the Motor Symptoms of Parkinson’s Disease?
People are usually more familiar with the motor symptoms of PD, as these are the signs of the disease that are noticeable from the outside. These symptoms, known as the “cardinal” symptoms of PD, include:
- Bradykinesia (slowness of movement) – slowing down and loss of spontaneous and voluntary movement
- Rigidity – unusual stiffness in a limb, the face or other body part
- Resting tremor – an uncontrollable movement that affects a limb when it is at rest and stops for the duration of a voluntary movement
Other motor symptoms also appear in PD:
- Postural instability – problems with standing or walking, or impaired balance and coordination
- Other physical symptoms, such as gait problems and reduced facial expression, may also occur due to the same disruption of movement that causes the better-known tremor and slowness
What Are the Non-motor Symptoms of Parkinson’s Disease?
Doctors are increasingly recognizing the presence and effects of other symptoms of PD that are sometimes called “non-motor symptoms” or “dopamine-non-responsive.” These symptoms are common and can have a major impact on Parkinson’s patients. They can include:
- Cognitive impairment – decline in ability to multi-task and/or concentrate and potentially decline in intellectual functioning
- Mood disorders – depression and anxiety
- Problems sleeping – REM Sleep Disorder, where individuals act out their dreams
- Low blood pressure when standing
- Speech and swallowing problems
- Unexplained pains, drooling and smell loss
Is Parkinson’s Disease Causing my Symptoms?
Even if you experience symptoms common among people with PD, they may in fact be brought on by a different condition. Consult a doctor if you notice a change in your body with no obvious cause. While visiting the doctor, try to be as specific as possible when describing your symptoms. You may be referred to a movement disorders specialist , a neurologist with particular expertise in PD and other movement disorders.
Dr. Joseph Jankovic , a member of the MJFF Scientific Advisory Board , developed the screening questionnaire we use to help determine PD and parkinsonism (a range of neurological disorders that resemble PD).
Remember: Parkinson’s disease is rare. Even if your answer to several of these questions is yes, it’s more likely that you don’t have Parkinson’s than that you do. The most important step you can take is to see your doctor and get information about what is causing your symptoms.