Parkinson's disease is a slowly progressive neurologic condition characterized by involuntary trembling (tremor), muscular stiffness or inflexibility (rigidity), slowness of movement and difficulty carrying out voluntary movements. Degenerative changes occur in areas deep within the brain (substantia nigra and other pigmented regions of the brain), causing a decrease in dopamine levels in the brain. Dopamine is a neurotransmitter, which is a chemical that sends a signal in the brain. Parkinsonian symptoms can also develop secondary to hydrocephalus (a condition in which the head is enlarged and areas of the brain accumulate excessive fluids, resulting in an increase in pressure on the brain), head trauma, inflammation of the brain (encephalitis), obstructions (infarcts) or tumors deep within the cerebral hemispheres and the upper brain stem (basal ganglia), or exposure to certain drugs and toxins. Parkinson's disease is slowly progressive and may not become incapacitating for many years.
Parkinson’s disease generally begins with a subtle slight tremor, especially in the hands. At first, the tremor occurs at rest, then becomes more pronounced with fatigue and emotional stress, lessening during voluntary movements. The tremor may be limited to the arms or extend to the neck, jaws and legs. Voluntary movements such as walking become increasingly difficult.
Walking becomes slow, stiff and shuffling. Perception, thinking processes and sensation generally remain normal, although some patients may experience a reduction of intellectual abilities (dementia). The depression that sometimes develops in Parkinson’s disease may be part of the disease or a reaction to it.
As the disease advances, a stooped posture and an immobile, unblinking facial expression with frequent drooling may develop. Oily skin (seborrhea) may be present on the face and scalp. A feeling of being “frozen” in a position, unable to make a voluntary movement, is a repeated symptom of Parkinson’s disease.
The cause of Parkinson’s disease is unknown in most cases. A few cases of parkinsonism have resulted from carbon monoxide or manganese poisoning. Drug-induced parkinsonian symptoms can develop from drugs used to treat psychiatric disorders (dopamine-receptor antagonistic drugs). These symptoms usually disappear when the drugs are withdrawn or the dosage is decreased, or with time during treatment. A few families with multiple cases of Parkinson’s disease have been identified. Scientists have identified the general region where the defective gene that they believe causes these cases of Parkinson’s disease may be located. The gene has been located on the long arm of chromosome 4(q21-q23). Molecular geneticists believe the gene is essential for production of the protein called alpha synuclein. Others believe they have located a second gene on Chromosome 2 that may be responsible for Parkinson’s disease occurring in families.
In two studies reported in early 2005, investigators found that a mutation in the gene LRRK2 appears to occur in at least one of every 60 people who have the disease. Overall, the mutation could be responsible for up to 5 percent of Parkinson’s disease in people with a family history of the disease and may account for 1.5 to 2 percent of cases in individuals who do not have a family history of the disease.
Although 10 to 20 percent of all cases of Parkinson’s disease are diagnosed in individuals under the age of 40 years, this disorder occurs primarily in the middle-aged and elderly population. Parkinson’s disease affects approximately 1 percent of people over the age of 65. There are approximately 500,000 cases of classic Parkinson’s disease in the United States. About 50,000 new cases are reported every year. As the National Institute of Neurological Disorders and Stroke reported in a study of major neurologic disorders in biracial populations, the occurrence of Parkinson’s disease shows no gender (male to female) or racial differences.
Treatment for the symptoms of Parkinson's disease may include any or a combination of medications, surgery, or physical therapy.
The Food and Drug Administration approved the drug rasagiline (Azilect) in July 2006 for the treatment of Parkinson's disease. Azinlect functions by blocking the breakdown of dopamine, which is the chemical that sends information to the parts of the brain that control movement and coordination.
The U.S. Food and Drug Administration (FDA) has approved apomorphine (APOKYN) as an injectable drug for treating Parkinson's patients during episodes of “hypomobility”, the “off periods” when the patient becomes immobile or unable to perform activities of daily living. APOKYN was given priority review because injectable apomorphine is the first therapy approved to treat these episodes as they are happening (acutely). APOKYN was designated an orphan product.
A number of medications provide degrees of symptomatic relief for individuals with Parkinson's disease. These include levodopa, anticholinergic drugs, and amantadine, a dopamine-releasing agent that acts in coordination with levodopa. Anticholinergic agents such as trihexyphenidyl, benztropine mesylate, biperiden and diphenhydramine help control tremors and rigidity. Amantadine hydrochloride helps reduce tremors and rigidity and improves spontaneous movements. Bromocriptine (Parlodel) and/or pergolide (Permax) may be useful in some cases, particularly in conjunction with other drugs such as the combination of levodopa and carbidopa (Sinemet).
The treatment of choice is a combination of levodopa, which is an amino acid, and a precursor of the neurotransmitter dopamine, carbidopa (an enzyme inhibitor). This drug (Sinemet) tends to become less effective over time. Some doctors have suggested that patients try to prevent the “on-off” phenomenon by taking Sinemet an hour before meals since protein is found in almost all foods composed of amino acids which compete with levodopa for access to the brain. However, since many Parkinson's patients are debilitated due to the combined effects of the disease and aging, and may also have difficulty eating regularly due to tightened throat muscles, good nutrition is often difficult to maintain. Therefore, depleting protein in the diet of Parkinson's patients could be harmful or dangerous. Proper diet will permit absorption of the drug by the brain's receptor cells so that the protein in the meal will have much less effect on the drug's usefulness. If patients experience nausea with this method, they can take the drug with soda crackers or a similar non-protein snack.
A tablet combining levodopa, carbidopa, and entacapone known as Stalevo was approved in September 2003 for patients who experience signs of wearing off of drug effectiveness. Entacapone extends the time levodopa is active in the brain. For information about Stalevo, contact the manufacturer, Novartis Pharmaceuticals Corporation.
Bromocriptine (Parlodel) and pergolide (Permax), both mentioned above, are dopamine agonists that may supplement or, in some cases, be used as substitutes for Sinemet therapy. Dopamine agonists provide dopamine-like effects by stimulating areas on the surfaces of certain nerve cells (neurons) that bind to the neurotransmitter dopamine (dopamine receptors). There are several types of dopamine receptors, including those known as D1, D2, D3, etc. D1 and D2 dopamine receptors appear to function together to control movements. Bromocriptine stimulates D2 receptors, whereas pergolide stimulates D1 and D2 receptors and has some D3 activity.
Ropinirole (Requip), a D2 dopamine agonist, has been approved for use as a treatment for individuals with early Parkinson's disease without levodopa therapy and for individuals with advanced Parkinson's as an adjunct to levodopa therapy. Ropinirole stimulates D2 and D3 dopamine receptors. In one study, Requip successfully managed symptoms associated with Parkinson's disease for up to five years. In addition, there was a low risk of developing severe, uncontrollable, jerky body movements (dyskinesia), despite prolonged use of the drug. Requip is manufactured by GlaxoSmithKline.
The dopamine agonist pramipexole (Mirapex) has been approved by the Food and Drug Administration (FDA) for the treatment of Parkinson's disease. Mirapex is distributed by the Pharmacia Corp. Pramipexole also stimulates D2 and D3 dopamine receptors.
Treatment guidelines established in June 2001 recommend using dopamine agonists to treat early-stage Parkinson's disease and adding levodopa to treatment as the disease progresses. The reason for this is that some patients experience a motor side effect resulting in severe jerky body movements (dyskinesia) when taking levodopa.
In a small number of cases some people taking Mirapex and Requip for Parkinson's disease have reported irresistible sleep attacks that come on suddenly and without warning. Patients taking these drugs are advised not to drive until they have been taking the drugs long enough to learn if they may be susceptible to sleep attacks.
The drug tolcapone (Tasmar) has been approved by the FDA for the treatment of Parkinson's disease. Tolcapone is manufactured by Hoffman-LaRoche, Inc.
The orphan drug selegiline (Eldepryl) was approved for marketing by the Food and Drug Administration (FDA) in 1989. This drug is a monoamine oxidase inhibitor that may be used in late-stage Parkinson's disease in combination with levodopa and carbidopa. More recent research suggests that Eldepryl given to people with early-stage Parkinson's disease may delay the need for stronger drugs such as Sinemet. Due to potential serious side effects, the Food and Drug Administration has recommended avoiding the combination of Eldepryl with tricyclic or SSRI-type antidepressant drugs.
Surgery may be considered as an option for patients who have been treated with medications and no longer find that approach satisfactory. Two procedures that have been used are pallidotomy and thalamotomy, both of which involve surgical destruction of brain tissues. Deep-brain stimulation is a newer surgical procedure that has become a preferred surgical option.
A brain implant device, Activa Tremor Control System, has been approved by the FDA to help control drug-resistant tremors in individuals with essential tremor and Parkinson's disease. The device is an electrode that is implanted in the thalamus to cause deep-brain stimulation. Initial studies have shown that deep-brain stimulation is as effective as thalamotomy and has fewer negative effects. More studies are needed to determine the long-term safety and effectiveness of this device as a symptomatic treatment for essential tremor and Parkinson's disease. Studies are also needed to determine the effect on individuals when it is necessary to replace lead wires and the long-term effects of electrical stimulation on brain tissue. See the Investigational Therapies section of this report for information on current studies regarding deep-brain stimulation.
Physical therapy for individuals with Parkinson's disease may include exercises for speaking, swallowing, and overall muscle tone. Exercises will not stop the disease's progression but may reduce disability. Exercise may also improve an affected individual's emotional well-being.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources, contact:
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