Unknown: Parkinson Disease
Unknown: Parkinson Disease
Parkinson disease, or PD, is an age-related movement disorder characterized by tremor (repeated rhythmic shaking or trembling); short, jerky movements and muscular rigidity; difficulty keeping one's balance; walking with a stooped posture and without the associated arm swinging; and slowing down of voluntary movements. It is named for James Parkinson (1755–1824), a British doctor who first described it in 1817.
Parkinson disease is a disorder that affects the patient's ability to move smoothly and at a normal rate. It is a progressive disease, meaning that the symptoms get worse over time. It develops gradually over a period of years (usually about twenty years) and tends to affect only one side of the body at first. Patients may notice trembling or shaking in only one hand, which comes and goes and usually disappears during sleep. The tremor might involve the lips or chin rather than the hand. Patients might also notice a slight dragging of one foot when they walk. Other early symptoms include fatigue, depression, constipation, and sleep
problems; none of these are unique to PD and are often attributed to other disorders or simply to the aging process.
The next symptoms to appear are typically increasing difficulties with gait (a person's normal pattern of walking), coordination, and keeping one's balance. Some patients notice that it takes them longer to get dressed, to write notes, or complete other tasks that require flexibility in their hands. They may find that they cannot type or play the piano without making many more errors than they used to.
Most patients with PD eventually develop depression, anxiety, memory loss, and problems with speech or swallowing as well as difficulties with movement. Although it is unusual for patients with Parkinson disease to suffer from dementia (loss of thinking and problem-solving abilities in the early stages of the disorder, some do develop dementia—including hallucinations—in its later stages.
Parkinson disease is almost entirely a disorder of older adults. It is one of the most common movement disorders in the elderly, affecting about 1 percent of adults over sixty in the United States. It is rare for people younger than forty to be diagnosed with PD. Worldwide, the frequency of Parkinson disease is thought to be about 120 persons in every 100,000.
Men are one-and-a-half times as likely as women to develop Parkinson disease. PD appears to affect most races and ethnic groups equally. There are a few exceptions, such as the Parsis population in India, which have a higher than average rate of PD.
People who have a parent or sibling with Parkinson disease have a slightly increased risk (5 percent) of developing the disease themselves.
The cause or causes of Parkinson disease are not completely understood. Seven different gene mutations have been identified since the 1990s in Italian, Greek, English, and German families with a history of PD. Researchers are not yet certain, however, whether there are additional genes that play a role in the development of PD, and if so, how they interact to produce the symptoms of the disease. Another area of research is the role of pesticides in possibly triggering PD, although this theory is still debated. It is clear, however, the many people developed Parkinsonism after the influenza pandemic in 1918–1919, but the modern strains of influenza do not have this association.
What is known is that the tremor and other muscle-related symptoms of Parkinson disease are caused by damage to a part of the brain called the substantia nigra. The cells in this area produce a chemical called dopamine, which transmits nerve signals between the substantia nigra and another part of the brain that governs movement. Most Parkinson patients have lost 60 to 80 percent or more of the dopamine-producing cells in the substantia nigra by the time the first symptoms appear. The reason for the loss of these cells, however, has not yet been identified.
There are four symptoms of PD that are considered primary symptoms:
- Tremor. This is often the symptom that prompts patients to see their doctor.
- Muscle rigidity. Some patients with PD have muscles that are so stiff they cause pain.
- The slowing down of normal voluntary movements.
- Impaired balance. The patient may walk with a shuffling gait as well as being at high risk of falling. This symptom is usually the last of the primary symptoms to appear, usually about eight years after the early symptoms.
Other symptoms that may or may not occur in patients with PD include:
- The face lacks expression; may look like a mask.
- Anxiety and depression. Many patients become fearful and insecure in social situations, or irritable and moody.
- Difficulty with swallowing and chewing. The patient may drool or have difficulty eating enough food to maintain good nutrition.
- Speech problems. About 50 percent of patients with PD have difficulty talking; they may slur their speech, speak too softly, or speak too fast.
- Skin problems. The skin may become either very oily or extremely dry.
- Heavy sweating.
- Difficulty sleeping. The patient may have difficulty falling asleep at night, have vivid nightmares, or may fall asleep suddenly during the day.
- Dementia and cognitive (thinking-related) problems. The dementia that occurs in PD may affect the patient's memory, language, reasoning, or other mental skills; it occurs in about 30 percent of patients.
The diagnosis of Parkinson disease can be difficult because there is no single diagnostic test for the disorder. The symptoms of PD can occur with several other disorders, including stroke, head injuries, carbon mon-oxide poisoning, the side effects of certain medications, and hydrocephalus. Misdiagnosis is not unusual; in the recent past, when diagnosis was based on the patient's having two of the four primary symptoms of PD, the diagnosis was incorrect in 25 percent of cases.
The diagnosis of PD is usually based on taking the patient's history, including a family history of Parkinson disease if any, and a medication history. Blood tests and imaging studies are not helpful because the results are usually normal in patients with Parkinson disease. In some cases the doctor may need to see the patient several times over a period of months to determine whether the symptoms are consistently present.
The patient may be referred to a neurologist who specializes in movement disorders for a detailed evaluation. The specialist will examine
the patient's reflexes and other parts of the nervous system as well as the ability to move normally. The patient might, for example, be asked to walk across the room and back, write a note, or perform other simple tasks involving the hands. The findings that are considered the most accurate indicators of PD are:
- Two or more of the following primary symptoms: tremor, muscle rigidity, and slowed motion.
- Symptoms on only one side of the body.
- Tremor that is more noticeable when the patient's hands are resting in the lap than when they are moving.
- A strong response to levodopa, a drug that is used to treat PD.
To date, there is no cure for Parkinson disease. Medications are the first line of treatment for PD. The first drugs that are prescribed are drugs that give the person greater control over muscle rigidity and other movement problems, especially levodopa, a drug that is taken by mouth which the body can convert into dopamine. However, levodopa can have serious side effects, including involuntary movements, mental confusion, and hallucinations. In addition, it usually works for only four to six years before it starts to lose its effectiveness in controlling the patient's symptoms.
Other drugs that may be given include drugs like bromocriptine; they mimic the effects of dopamine on the brain rather than being converted into dopamine itself. Still other drugs may be given to inhibit the effects of an enzyme in the brain that breaks down dopamine. These drugs help to prolong the effects of levodopa and may eventually allow the doctor to reduce the person's dose of levodopa. A newer medication, selegiline, appears to slow down the destruction of the cells in the substantia nigra, and is often given to patients in early-stage PD.
In addition to drugs to help the patient control movement, the doctor may also prescribe antidepressants if the person has become depressed, or antipsychotic medications if the person is having hallucinations. The types of drugs prescribed and the dosages are individualized, since patients diagnosed with PD do not all have the same symptoms with the same severity.
There are some surgical treatments used for patients with advanced PD. One option is surgery that destroys specific parts of the brain that contribute to tremor or muscle rigidity. This type of surgery is
permanent, however, and has been largely replaced by deep brain stimulation or DBS. DBS is a procedure in which an electrode is implanted within the brain and connected to a pulse generator implanted beneath the patient's collarbone. The pulse generator stimulates the brain periodically with a mild electrical current that eases at least some of the symptoms of Parkinson disease. DBS cannot, however, be used with people with memory problems, hallucinations, a poor response to levodopa, severe depression, or general poor health.
Physical therapy, occupational therapy, speech therapy, and support groups are also recommended forms of treatment for PD.
PD is not by itself a fatal disease but gets worse over time; in the later stages of the disease, PD may cause complications like choking, pneumonia, and falls that can lead to the patient's death. The speed of progression varies from patient to patient; some patients may be able to function relatively well for nearly twenty years after diagnosis while others become completely dependent on caregivers within a few years. There is no way to predict how quickly the disease will progress in an individual patient. Patients who are diagnosed with Parkinson disease are usually advised to plan ahead for the time when they may require a full-time caregiver or transfer to a nursing home.
There is no known way to prevent Parkinson disease because its causes are still being investigated.
One area of investigation in Parkinson disease is the search for a bio-marker (abnormal body chemical) in patients with PD that could be used as a screening tool to identify people at increased risk of developing the disease before the first symptoms appear. Another area of research is the use of an imaging technique called positron emission tomography (PET). PET may allow scientists to understand more about the disease process and the possible causes for the loss of the nerve cells that produce dopa-mine. Still a third field of investigation is the hunt for additional genes and gene mutations involved in PD.
SEE ALSO Alzheimer disease; Depression; Hydrocephalus; Stroke
WORDS TO KNOW
Biomarker : A substance produced by the body that is distinctive to a particular disease and can be used to identify its presence or track its progress.
Dementia : Loss of memory and other mental functions related to thinking or problem-solving.
Dopamine : A chemical produced in the brain that is needed to produce smooth and controlled voluntary movements.
Gait : A person's characteristic pattern of walking.
Tremor : An unintentional shaking or trembling movement. Tremor is a characteristic symptom of PD.
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