Overview
Parkinson's disease is a disease of the nervous system that causes people
to lose control over their muscles. About one in every 250 people over the
age of 40, and about one in every 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.
In itself, Parkinson's is not a fatal condition. However, the end-stage of
the disease can lead to pneumonia, choking, severe depression, and death.
Causes
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 the stem of the brain (the basal ganglia).
In Parkinson's, dopamine-producing cells in the brainstem are lost. In most
cases, we don't know why. Primary Parkinson's disease is the diagnosis
in the majority of cases where the doctor doesn't know why these cells are dying.
Secondary Parkinsonism is due to some disease 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 and confusion
in the elderly
- metoclopramide, a commonly prescribed anti-nausea drug
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 in the years 1918 to 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. However, a major U.S. 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.
Symptoms
The first sign of Parkinson's in most people is a trembling hand. Later,
the arms and legs may be affected. The jaw, tongue, eyelids, and forehead may
also show signs of the condition. Tremors only appear at rest, and not when
the person is making purposeful movements. About 25% of people with Parkinson's
don't have tremors; rather, they find their limbs or other areas turning stiff
or rigid. Most people, however, have both. The rigidity becomes worse as the
disease progresses, making movement difficult.
The balance reflexes tend to become impaired, making it difficult to turn quickly
or negotiate narrow corners and doorways. It's often hard to make an initial
movement with the foot when wanting to walk.
The following symptoms are common in Parkinson's, though no one person will
have all of them:
- abnormal gait
- decreased arm swing
- excessive salivation
- feelings of depression or anxiety
- general slowness of movement
- increase in dandruff or oily skin
- lack of facial expression (hypomimia)
- less frequent blinking and swallowing
- lowered voice volume (hypophonia)
- slight foot drag
- slow reflexes if pushed off balance
- small cramped handwriting (micrographia)
- stiffness of limbs
- stooped posture
- tremor when resting
Depression is common in Parkinson's sufferers. People with Parkinson's run
a higher risk of developing dementia, which often results in problems with memory
or concentration similar to what is seen in Alzheimer's disease.
Treatment
Anyone who has Parkinson's will eventually end up taking a medication containing
levodopa.* Dopamine, the substance that's in too-short supply for these
sufferers, can't be given directly. It can't cross the blood-brain barrier,
a lining that insulates the brain from the rest of the body. Levodopa does get
into the brain, where it is converted to dopamine, which is then used to replace
the missing dopamine and improve control of movements.
Levodopa has some drawbacks, however. After about 2 to 5 years on the drug,
many people find that it has become less effective. They may suffer alternating
bouts of disabling stiffness and uncontrolled movements called dyskinesias.
Some doctors believe this is due to the levodopa and may wait to prescribe it
until Parkinson's has progressed. Others argue that it's part of the natural
process of the disease, and prescribe levodopa immediately to improve the patient's
quality of life.
Levodopa can have other side effects, including hallucinations and nightmares.
It's often given with another drug, such as carbidopa or benserazide, that allows
smaller doses of levodopa to deliver more benefit.
Fortunately, new medications for Parkinson's are being released that may help
people in addition to levodopa. These include bromocriptine, pergolide, pramipexole,
and ropinirole. Rather than replacing dopamine, these drugs directly stimulate
the areas that usually respond to dopamine.
For patients who have a hard time moving despite (or because of) levodopa,
there are surgical options. Pallidotomy usually results in a temporary
improvement that lasts for a number of years. On the other hand, it involves
deliberately damaging part of the brainstem.
There are many busy avenues of research in Parkinson's - and some promising
experimental results. Deep brain stimulation is an area of particular focus.
An electrical charge is sent through a wire to the base of the brain. A small
surgically implanted battery is at one end of the wire. Exactly where in the
brain the other end should go is the subject of current research. Several areas
have shown promise. Stimulation of the thalamus has been approved in the U.S.
since 1997. It's effective for tremors but not for rigidity. Stimulating other
parts of the brainstem may turn out to be more effective. However, there's a
small risk of dangerous bleeding in the brain.
Regular exercise and physical therapy can help stave off loss of motor control.
Keeping active and eating a good diet are vital in the management of Parkinson's
disease.
*All medications have both common (generic) and brand names. The brand name
is what a specific manufacturer calls the product (e.g., Tylenol®).
The common name is the medical name for the medication (e.g., acetaminophen).
A medication may have many brand names, but only one common name. This article
lists medications by their common names. For more information on brand names,
speak with your doctor or pharmacist.
Other tips:
There's no definitive test for Parkinson's disease. Diagnosis is based
purely on the symptoms and a physical examination. The fact that trembling in
Parkinson's is at its worst when the muscles are resting distinguishes it from
other kinds of tremors. People with Parkinson's also tend to have an odd gait
or walk, which is stooped and shuffling with little or no spontaneous arm swinging.
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