Treatment options for Parkinson’s disease

This review explained the different types of treatment available for Parkinson’s disease. The authors outlined several types of oral medications and surgical treatments used to treat motor based symptoms.

Parkinson’s disease (PD) is a progressive degenerative disorder where the number of dopamine-producing nerve cells in the brain are reduced or impaired. This means there is a reduction in the amount of dopamine, as well as other chemicals in the brain, which can lead to symptoms that can be physical and/or cognitive. There are a wide range of symptoms caused by PD, therefore it is important for patients to be aware of the different types of treatments available.

This review summarised a lot of the different treatments available to treat PD symptoms.

Levodopa is one of the most common treatments used for PD. It works by helping the body make the chemical dopamine, which is normally reduced in PD. An increase in dopamine leads to a reduced number of tremors and can improve a patient’s motor function. Levodopa is normally taken with other treatments, such as carbidopa, that work to localize the dopamine production to the brain therefore reducing side effects of dopamine in the bloodstream.

As this is a long term treatment, there are many side effects linked to continued levodopa. These include dyskinesias (abnormal involuntary movement), nausea, hypotension (low blood pressure), hallucinations and dopamine dysregulation syndrome (addictive behaviors).

Monoamine oxidase B inhibitors (MOA-B inhibitors) are used to block chemicals that naturally break down dopamine in the brain. Clinical trials show that these drugs are beneficial at improving motor function in PD patients. They have been used as an add-on therapy combined with levodopa to increase effectiveness. Side effects of these drugs include dizziness, headache and constipation.

Catechol-O-methyl transferase inhibitors (COMT inhibitors) are also used to block chemicals that naturally break down dopamine. Entacapone (Comtan) and tolcapone (Tasmar) are used to boost the effectiveness of levodopa. Common side effects include nausea, orthostatic hypotension (low blood pressure after standing up), urine discoloration and diarrhea. There have been rare incidences of fatal liver problems after treatment with tolcapone, therefore monitoring liver function is advised.

Amantadine (Symmetrel) is an antiviral drug usually used to treat the influenza virus. It has been shown to be effective at treating dyskinesias and fatigue in PD patients when used in combination with levodopa. Side effects include nausea, dry mouth, ankle edema (swelling), mottled skin, hallucinations and confusion.

Anticholinergics are used to treat tremors in PD patients. They may also be effective at treating sweating and sialorrhea (excessive saliva production). They are not commonly used due to the frequency of side effects such as hallucinations and cognitive impairments.

Dopamine agonists carry out the same role as dopamine in the brain. They are usually recommended for early stage PD as they last longer in the body than levodopa and have a lower rate of dyskinesias. In later stages however levodopa treatment is usually added. Side effects include orthostatic hypotension, nausea, ankle edema, dizziness, excessive daytime sleepiness and other sleep disturbances. Other side effects involve impulse control problems, and patients can experience hypersexuality, compulsive gambling and binge eating.

For patients with advanced PD, continuous delivery of levodopa or a dopamine agonist called apomorphine (Apokyn) via pump is possible. This can be used to treat patients with severe motor fluctuations (periods with no response to medication), however the same side effects are seen.

Deep brain stimulation (DBS) uses implanted electrodes to stimulate targeted parts of the brain to block the signals that cause some of the motor symptoms that occur in PD patients. This type of treatment is used for patients with advanced PD and severe motor complications that cannot be controlled by oral medications. DBS has been shown to improve motor function and can also improve tremor even when levodopa and other medications have failed. In some cases, DBS treatment can reduce treatment fluctuations leading to a reduction in oral medication dose,s however this depends on the area of the brain being stimulated.  Side effects are mainly psychiatric such as depression and anhedonia (inability to feel pleasure). Other less common side effects from stimulation include dysathria (difficult speech), paresthesia (prickling sensation felt in the limbs) and apraxia of the eyelid (difficulty opening eyelid). As it involves brain surgery, normal surgical risks such as hemorrhage or infection can also occur.

The authors of this review highlighted the broad range of treatments available for PD. They specified the side effects associated with each medication and outlined different treatments for early and late stage PD.