What treatment options are available for Parkinson’s disease (PD)?
A variety of medications is available for the treatment of PD symptoms. The most powerful drug for treatment of PD symptoms is levodopa, a chemical found naturally in plants and animals. Nerve cells can use levodopa to make dopamine, which replenishes the low amount in the brain. Levodopa is often used in combination with carbidopa (Sinemet®) to prevent or diminish some of the side effects of the medication. However, there are concerns about the long-term side effects of levodopa, especially the development of involuntary movements (dyskinesias) which can be disabling. Newer medications, such as the dopamine agonists, are much less likely to produce dyskinesias. As a result, most experts recommend against using levodopa early in the course of the disease and to use dopamine agonists instead. If the patient cannot get sufficient relief with the dopamine agonists, particularly the newer generation of dopamine agonists, levodopa/carbidopa (Sinemet) can be added.
Dopamine agonists, such as the newer generation ropinirole (Requip®) and pramipexole (Mirapex®) and the older agent, bromocriptine (Parlodel®), are agonist drugs used to treat PD. These drugs mimic the role of dopamine in the brain and work by stimulating certain parts of the brain and nervous system. They can also be used in combination with levodopa, but are generally less effective in controlling rigidity and bradykinesia. Most experts will use these medications first and only add levodopa if the symptoms cannot be controlled sufficiently.
Another class of drugs used to treat the symptoms of PD is called COMT inhibitors because they block an enzyme that breaks down levodopa and dopamine. Examples of these are tolcapone (Tasmar®) and entacapone (Comtan®). Alone, the medications aren't helpful, but they work well in combination with levodopa. Tolcapone and entacapone slow the body's ability to get rid of levodopa, so it lasts longer and is more consistent. Because they increase the effectiveness of levodopa, tolcapone and entacapone may also increase its side effects, such as involuntary movements. Tolcapone has been associated with liver failure and is thus rarely used. When tolcapone is used, regular blood monitoring for liver damage is required. Other medications include amantadine (Symmetrel®), selegiline (deprenyl), and rasagiline (Azilect®). These drugs can be used in early PD on their own or can be combined with levodopa later in the course of the illness.
There are now a number of safe and effective surgical options available for the treatment of PD. Generally, surgery is only considered when medication cannot provide adequate control.
Deep brain stimulation involves placing an electrode permanently in one of three locations deep in the brain. The electrode is then connected to a type of pacemaker implanted under the skin on the chest. Once activated, the device sends continuous electrical pulses to the targets, blocking the impulses that cause tremors. Deep brain stimulation has many significant advantages. First, it does not require purposeful destruction of any part of the brain and therefore, has few complications. Deep brain stimulation is adjustable and can be changed as the patient's disease or response to medications change. If deep brain stimulation is causing excessive side effects, the stimulator can be turned off and the effects reverse, which is not the case with older destructive surgeries.
Older surgeries required the purposeful destruction of parts of the brain and had a higher risk of complications. They are rarely done today. In pallidotomy, a small section of the brain that is overactive due to PD is permanently destroyed using surgical techniques. This treatment can eliminate rigidity and significantly reduce tremor, bradykinesia, and balance problems. Thalamotomy is a similar procedure where a section of the thalamus, the part of the brain that controls messaging, is destroyed using surgical techniques. This treatment is used only to control tremors and is not generally recommended because of better targets.
Clinical Trial Participation
There are now several treatment options being tested for PD. These include:
- Medications that slow the progression of disease or alleviate the symptoms of PD.
- Surgical procedures that look into other brain targets or test new devices.
- Non-pharmacological interventions such as exercise, physical, behavioral, and cognitive therapy.
Most of these "clinical trials" allow the Parkinson patient to continue with their usual medications while participating in the study. During clinic visits, patients and their caregivers should ask their health care provider if some of these clinical trials are available as an option. Participating may improve their care while contributing to the advancement of PD treatment.