In 1817, the British doctor James Parkinson wrote "An Essay on the Shaking Palsy," in which he described a disease that caused its sufferers to shake uncontrollably, but that left their intellect unharmed [source: European Parkinson's Disease Association]. In the 1850s, French neurologist Jean-Martin Charcot named the disease in honor of the man who had first described it -- Parkinson's disease.
Like Alzheimer's, Parkinson's is a neuro-degenerative disease. It damages nerve cells (neurons) in a part of the brain called the substantia nigra. Normally, these cells produce the chemical messenger (neuro-transmitter) dopamine, which enables the muscles to move smoothly. When 80 percent of the nerve cells in the substantia nigra become damaged or die, the result is the rigid, shaky and stiff movements that are the hallmark symptoms of Parkinson's.
Parkinson's is one of several conditions called motor system disorders, which affect dopamine-
producing cells in the brain. Other conditions in this category cause symptoms similar to those of Parkinson's disease (called parkinsonism), but they tend to get worse faster and don't respond as well to medications used to treat Parkinson's. These conditions include:
Progressive supranuclear palsy (PSP) is a rare disorder that causes clumps of cells at the base of the brain to die. This leads to rigid movements and poor balance. What distinguishes PSP from Parkinson's is that it also prevents the eyes from moving up and down. Because they can't look down, people with this condition are more likely to fall.
Multiple system atrophy (MSA) is less common than Parkinson's and tends to worsen more quickly. It involves a combination of symptoms -- the rigidity, loss of balance and lack of muscle control seen in Parkinson's, as well as a disruption in autonomic (not under conscious control) functions such as blood pressure, heart rate and digestion.
Dementia with Lewy bodies occurs when abnormal protein deposits called Lewy bodies form on nerve cells. It is the second most common type of dementia, afterPage S Alzheimer's [source: PubMed]. Its symptoms are a combination of those of Parkinson's and Alzheimer's disease, ranging from movement difficulty and tremor, to confusion and memory loss.
Vascular parkinsonism involves many of the same symptoms of Parkinson's disease (stiffness, rigidity and difficulty with balance). However, vascular parkinsonism is caused by a series of small strokes that block the vessels that feed the brain with oxygen-rich blood.
Drug-induced parkinsonism involves Parkinson's symptoms caused by drugs such as antipsychotic medications like metoclopramide, reserpine or tetrabenazine. The symptoms usually improve once the drug is stopped.
Potential Causes of Parkinson's Disease
About 1.5 million Americans have Parkinson's disease and 60,000 more are diagnosed with it each year [source: National Parkinson Foundation]. Most people who get the disease are older than 60, but about 15 percent are diagnosed before age 50 [source: National Parkinson Foundation].
Although doctors don't know what exactly causes Parkinson's, they think it stems from a combination of genetic and environmental factors. In about 5 to 10 percent of patients, there is a strong family history of the disease [source: National Parkinson Foundation]. Parkinson's may affect the same generation (siblings), or two different generations (parent and child) in this small percentage of familial cases.
Other possible causes of Parkinson's (and conditions like it) include:
Toxins: Scientists have linked exposure to manganese, carbon monoxide, cyanide and some pesticides and herbicides with a higher Parkinson's risk [sources: National Parkinson Foundation, Mayo Clinic]. However, most people with the disease haven't been exposed to these substances.
A virus: In the early 1900s, people who came down with a form of the encephalitis virus became stuck in a trancelike state in which they couldn't move or speak. When neurologist Dr. Oliver Sacks treated these people with levodopa, the same medication used to treat Parkinson's, they briefly came "back to life." (These "Awakenings" were depicted in the 1990 movie starring Robin Williams.)
Head trauma: Boxer Muhammad Ali, one of the most famous Parkinson's sufferers, developed the disease when he was only in his 40s. Researchers have been studying whether trauma to the head may play a role in the development of the disease.
Structural problems: Strokes and hydrocephalus (fluid buildup in the brain) are two conditions that may lead to an increased risk of parkinsonism.
Parkinson's Symptoms and Diagnosis
As the disease slowly destroys nerve cells in the brain, the first symptoms of Parkinson's appear. The four hallmark symptoms are tremor (shaking) of the hands, arms, legs and face; slow movement (bradykinesia); stiffness; and difficulty with balance and coordination.
The disease is different in each person. Some people may become completely disabled relatively quickly, while others have only minor symptoms and get worse very gradually. In general, the symptoms will progress until the person notices distinct changes in his or her ability to walk, talk and perform other everyday activities. In the later stages of the disease, people with Parkinson's can develop a shuffling walk, muffled speech, small and illegible handwriting, emotional changes (including depression), a blank stare, difficulty chewing and swallowing, and constipation.
No single test can identify Parkinson's disease. Usually diagnosing the condition is a matter of ruling out similar diseases with the same symptoms. The doctor will first take a thorough health history and do a neurological test. Blood tests and magnetic resonance imaging (MRI) scans can rule out other diseases. People with at least two of the four hallmark symptoms of Parkinson's disease, and who respond to the drug levodopa, are said to have the disease.
Doctors can stage the severity of the disease using the Hoehn and Yahr Staging and Unified Parkinson's Disease Rating Scale.
The Hoehn and Yahr scale helps doctors describe the severity of symptoms based on five stages:
- Stage 1 -- symptoms are only on one side of the body
- Stage 2 -- symptoms are on both sides of the body, but balance isn't impaired.
- Stage 3 -- there is some balance impairment and disability.
- Stage 4 -- disability is severe, but the person can still walk or stand without help.
- Stage 5 -- the person cannot stand or walk, and is wheelchair-bound or bedridden.
The Unified Parkinson's Disease Rating Scale helps doctors follow the course of Parkinson's by tracking:
- Intellectual impairment, depression, motivation
- Activities of daily living (speech, swallowing, handwriting, cutting food, dressing, hygiene and walking)
- Motor skills (speech, facial expression, tremor, rigidity, posture and walk)
Within each of these areas is a list of functions. Each function is rated on a four-point scale, from normal (0) to significant problems (4). There are a total of 199 points, with 0 being no disability and 199 being total disability.
For three decades, the mainstay of treatment for Parkinson's has been the drug levodopa. Nerve cells in the brain convert levodopa into dopamine, which relieves some of the tremors and stiffness -- the most common and troubling symptoms of Parkinson's. Because enzymes in the blood tend to break down levodopa before it can reach the brain, it's typically combined with the drug carbidopa, which keeps levodopa intact until it gets to the brain. Although levodopa is effective, it can cause side effects ranging from dry mouth to nausea and vomiting.
Drugs called dopamine agonists mimic the effects of dopamine in the brain. They stimulate the same parts of the brain that normally receive dopamine, so that the brain thinks it's getting dopamine. Dopamine agonists such as bromocriptine (brand name Parlodel), pramipexole (brand name Mirapex) and ropinirole (brand name Requip) can be used instead of levodopa or along with it, depending on the person's symptoms. In some people these drugs can increase the risk of compulsive behaviors, including gambling and sex.
Antivirals are normally used to treat diseases caused by a virus, but doctors have discovered that they can also relieve the symptoms of Parkinson's disease. Amantadine (brand name Symmetrel) is an antiviral drug that reduces tremor, slow movements and fatigue in Parkinson's patients. It can be given alone, or combined with levodopa or a dopamine agonist.
The first drugs used to treat Parkinson's were anticholinergic medications. They work by decreasing the activity of the chemical messenger acetylcholine which also controls movement. Anticholinergic medications can be taken alone or with levodopa and may help with tremors and rigidity in people with mild Parkinson's disease. However, anticholinergic drugs are rarely used in the elderly because they can cause confusion.
Monoamine oxidase-B (MAO-B) inhibitors like selegiline (brand name Eldepryl) and rasagiline (brand-name Azilect) inhibit an enzyme called monoamine oxidase B (MAO-B), which normally breaks down dopamine in the brain. By blocking the effect of this enzyme, MAO-B inhibitors enable both natural dopamine and levodopa to work longer in the brain. One downside to these drugs is that they can interact with other medications, including antidepressants, narcotic painkillers and decongestants.
The class of drugs known as catechol O-methyltransferase (COMT) inhibitors also blocks an enzyme that normally breaks down dopamine. The COMT inhibitor entacapone is often added to levodopa and carbidopa (the combination drug is called Stalevo) to help levodopa stay active in the brain for a longer period of time.
Although these drugs can help with symptoms, people who use them for long periods of time may find that the benefits come and go. They may have periods in which they can move smoothly, followed by periods in which they have trouble moving. This phenomenon is called "wearing off." Another side effect of using Parkinson's medications over the long-term is abnormal movements (dyskinesia). Eventually, the effects of medication become so limited that some people turn to surgery to relieve their symptoms. We'll find out about that, next.
Two types of procedures are used to treat Parkinson's: ablative procedures and deep brain stimulation (DBS). Ablative procedures like thalamotomy and pallidotomy use cold or heat to destroy a small area of brain tissue that is abnormally overactive in people with Parkinson's disease. Surgery on one side of the brain will affect the other side of the body.
In people with Parkinson's, the loss of dopamine-producing cells leads to abnormal activity in certain parts of the brain. Deep brain stimulation implants a thin electrode in the brain and attaches it to a battery-operated device called a neurostimulator (or pulse generator), which acts much like a heart pacemaker, sending impulses to correct the abnormal brain activity. DBS on one side of the brain affects symptoms on the opposite side of the body. The procedure doesn't affect dopamine production, so patients who have it will still need to take their medication, although they may not need to take as much.
In addition to medication and surgery, patients can get physical therapy to improve balance and movement, and speech therapy to help with speaking and swallowing. Parkinson's patients may also benefit from these alternative therapies and lifestyle changes:
- Massage, which reduces muscle tension and promotes relaxation
- Tai chi, which improves flexibility, strength and balance
- Yoga, which improves flexibility and balance
- Eating healthy (especially fruits, vegetables and fiber), which relieves the constipation that can be a symptom of Parkinson's
Several new therapies are under investigation for Parkinson's disease, and might lead to improved treatments in the future:
People with Parkinson's don't make enough coenzyme Q10, a substance that is essential for energy production in the cells. One study found that 1,200 milligrams a day of coenzyme Q10 reduced disability and slowed disease progression in Parkinson's patients [source: National Parkinson Foundation].
Many Parkinson's patients take vitamin E. Although research so far has not shown that vitamin E slows disease progression, this antioxidant fights cell damage caused by highly reactive molecules called free radicals.
Researchers from the National Institutes of Health (NIH) have been investigating whether creatine, an amino acid found in muscles, might improve patients' energy and muscle strength, and slow the progression of Parkinson's disease.
In early studies, the investigational drug SLV308 significantly improved tremors and slow movement in Parkinson's patients. Research, though preliminary, indicates that it might be useful in the early stages of the disease.
Stem cells, which can develop into any type of tissue in the body, are showing promise for many diseases, including Parkinson's. Researchers have already used stem cells to treat rats with symptoms of Parkinson's [sources: BBC News, MIT News]. The challenge is to coax the stem cells into becoming the damaged nerve cells, which will take more time and research.
Related HowStuffWorks Articles
More Great Links
- Dudley, David. "2006 Impact Awards." AARP Magazine, January/February 2006.
- Duenwald, Mary. "Parkinson's 'Clusters' Getting a Closer Look." The New York Times, May 14, 2002.
- European Parkinson's Disease Association. "James Parkinson." http://www.epda.eu.com/worldPDDay/jamesParkinson.asp.
- Factor SA and Weiner WJ. Parkinson's Disease: Diagnosis and Clinical Management. 14. Quantitative Measures and Rating Scales.
- Familydoctor.org. "Parkinson's Disease." http://familydoctor.org/online/famdocen/home/common/brain/disorders/187.printerview.html.
- HealthDay. "New Hope for Parkinson's Patients." http://www.nlm.nih.gov/medlineplus/news/fullstory_66163.html
- HealthDay. "Parkinson's Drugs Again Linked to Compulsive Disorders." http://www.nlm.nih.gov/medlineplus/news/fullstory_66244.html.
- Massachusetts General Hospital. "Hoehn and Yahr Staging of Parkinson's Disease, Unified Parkinson Disease Rating Scale (UPDRS), and Schwab and England Activities of Daily Living."
- Mayo Clinic. "Parkinson's Disease." http://www.mayoclinic.com/print/parkinsons-disease/DS00295/METHOD=print&DSECTION=all.
- National Institute of Neurological Disorders and Stroke. "NINDS Deep Brain Stimulation for Parkinson's Disease Information Page." http://www.ninds.nih.gov/disorders/deep_brain_stimulation/deep_brain_stimulation.htm.
- National Institute of Neurological Disorders and Stroke. Parkinson's Disease Information Page. http://www.ninds.nih.gov/disorders/parkinsons_disease/parkinsons_disease.htm.
- National Parkinson Foundation. "About Parkinson's Disease." http://www.parkinson.org/NETCOMMUNITY/Page.aspx?pid=225&srcid=201.
- Parkinson's Disease Foundation. "Medications and Treatments." http://www.pdf.org/AboutPD/med_treatment.cfm.