Parkinson's Disease
Parkinson's disease (PD) is a degenerative central nervous system (CNS) disorder characterized by uncontrolled body movements, rigidity, tremor, and gait difficulties. The American Parkinson Disease Association estimates that one million Americans are affected by the disease. The risk for developing PD increases with age, and onset usually occurs at around 50 years of age or older, although the disease is not unknown in people in their 30s and 40s. Parkinson's disease affects men and women equally. There are two types of Parkinson's disease: idiopathic PD and secondary PD. Idiopathic PD, also known as primary PD, has no known recognizable cause; secondary PD may result from trauma, tumor, or cerebrovascular disease, or may be drug induced. Patients with both types of PD are classified into stages (early, moderate, or advanced) based on the progression of disease. There is no known cure for the disease; rather, the treatment goal for patients with either form of PD is to control the symptoms and provide quality of life.
Parkinson's disease is actually a group of related CNS disorders caused by the destruction of the substantia nigra (pigmented brain cells), which produce dopamine (a neurotransmitter). The deficiency of dopamine results in the loss of muscle tone and voluntary muscle control seen in PD. Recent studies indicate that dopamine deficiencies in other areas of the brain and abnormalities of other neurotransmitters, such as norepinephrine and serotonin, may also contribute to the disease.
Signs and Symptoms
Although onset of PD can be rapid, it is generally insidious, with symptoms gradually progressing over a number of years until they interfere with daily activities. The four major symptoms of Parkinson's disease are
- Rigidity (stiffness when neck or extremities are moved).
- Resting tremor (involuntary movement of contracting muscles, especially when at rest).
- Bradykinesis (slowness in initiating movement).
- Poor posture and loss of balance.
Secondary symptoms of PD include
- Depression.
- Senility.
- Postural deformity.
- Speech difficulties.
- Emotional changes (patients become fearful or insecure).
- Memory loss and slowness of thought.
- Difficulty swallowing or chewing.
- Urinary dysfunction or constipation.
- Skin problems.
- Sleep disorders.
As PD progresses, patients develop a characteristic gait called festination, with which patients take small, hurried steps on tiptoe. Accidental falls occur frequently as a result of festination. As the disease progresses, it becomes more difficult for Parkinson's patients to manage daily activities, and full-time caregivers are often necessary.
Diagnosis of Parkinson's Disease
It is often difficult to diagnose the early stages of Parkinson's disease because the patient's symptoms may be vague. Often, diagnosis will be made only after the patient's tremors become readily apparent and one or more of the other classic symptoms appears. There is no specific test for the presence of the disease; rather, diagnosis is made on a thorough neurological examination. CT scans and MRIs may be ordered to rule out other diseases. There are multiple forms of PD, but the symptoms associated with all forms of the disease are similar. It is important to diagnose the specific form and the progression of PD because the treatment program will vary accordingly.
Conventional Treatment of PD
The treatment of PD patients is based on the type and stage of the disease, and is designed to alleviate symptoms. Some commonly used medications include anticholinergics (e.g., benztropine, biperiden, and orphenadine), dopamine receptor agonists (e.g., amantidine, bromocriptine, and pergolide), and monoamine oxidase (MAO) inhibitors, such as selegiline (deprenyl). Although deprenyl has been shown to be effective in the treatment of PD, recent research suggests that the effectiveness of this medication decreases over time. L-dopa, Sinemet, and Sinemet CR remain the most powerful medications for the treatment of PD, and are most often prescribed only during the advanced stage of the disease because their effectiveness decreases with time.
L-dopa can cross from the bloodstream to the brain and be converted to dopamine in the brain by the active form of vitamin B6. Dopamine itself cannot enter the brain from the bloodstream. Sinemet is L-dopa in combination with the peripheral dopa-decarboxylase inhibitor Carbidopa. Without the Carbidopa, dopa decarboxylase enzymes in the intestine would convert L-dopa to dopamine, which cannot enter the brain. Ropinirole, a synthetic, nonergot dopamine agonist receptor, has been shown to improve motor function and delay disability in PD patients. Ropinirole may be used prior to treatment with L-dopa.
Patients on long-term dopamine therapy may experience the on-off syndrome associated with the medication. During the on phase, dopamine levels in the brain are high and symptoms are controlled; during the off phase, dopamine levels in the brain decrease and the patient's symptoms return. These changes may be sudden and dramatic as dopamine levels fluctuate. The syndrome is particularly frustrating to PD patients, because there are no warning signs prior to the onset of either phase of the syndrome.
Because PD patients may experience sleep disorders and depression, sedatives and antidepressant agents may be prescribed. These medications should be used with caution in elderly patients, because of the increased risk for unsteadiness, confusion, and delirium.
