By Dr Ananya Mandal, MD
Parkinson’s disease is primarily treated using medications. Medicines may be used to treat the symptoms of Parkinson’s disease. These medicines can ease symptoms but do not cure the condition. The degree of responsiveness to the medication and the duration for which the effects persist varies between individuals.
The main types of medication are commonly used include:
This is a form of dopamine that is absorbed by the nerve cells of the brain and gets turned into active form of dopamine. It is usually taken as a tablet. Initial doses of levodopa are very small and as the response to the small dose wears off the dose is increased.
As such levodopa may be destroyed in the blood so that the brain may receive low amounts of active dopamine. This causes reduction in efficacy. For this levodopa is combined with other medication, such as benserazide or carbidopa. These agents stop the levodopa being broken down in the gut and increase the amount of active dopamine that reaches the brain. These agents also reduce the side effects caused by levodopa including nausea, vomiting, dizziness and fatigue.
Over time the efficacy of levodopa diminishes. This happens because as more nerve cells in the brain die and lesser numbers absorb the levodopa. Over long term use another side effect is seen. It is called the “on-off” effect. Here the patients may suddenly switch between being able to move (on stage) to being immobile (off stage). There may be uncontrollable, jerky muscle movements (called dyskinesias) as a side effect of levodopa as well.
Dopamine agonists may act as substitutes for dopamine in the brain and have a similar effect to levodopa. These agents include drugs like Bromocriptine. These agents have side effects including nausea, vomiting, fatigue, episodes of confusion or hallucinations etc. Newer non-ergot-derived agonists are preferred (pramipexole and ropinirole) over older agents bromocriptine, cabergoline, lisuride and pergolide.
Monoamine oxidase-B inhibitors or MAO-B inhibitors
This group includes drugs like Selegiline and Rasagiline. These agents block the effects of an enzyme called monoamine oxidase-B in the brain. MAO-B is normally responsible for destruction of dopamine. If the effects of this enzyme is blocked the action of the dopamine is prolonged. MAO-B inhibitors can improve the symptoms of Parkinson’s disease but are less effective than levodopa. They can cause side effects such as nausea, abdominal pain, headache etc.
COMT inhibitors include Entacapone and Tolcapone. These agents prevent levodopa from being broken down by the enzyme COMT. These agents can cause nausea, vomiting, liver problems and abdominal pain.
Amantadine can be used as monotherapy in early Parkinson’s disease. It has a weak and short-lived benefit. It is usually used in combination with other agents.
Medications are the usual method of treating Parkinson’s disease. However, surgery is sometimes used to treat long term patients. These surgical procedures are offered by selected centers. They may not be suitable for all patients.
The surgical treatment was developed in the mid-twentieth century before the advent of effective medical therapy. It still has a place in treatment and is under research these days.
Types of surgery
Deep brain stimulation is a surgical treatment sometimes used in patients with long term Parkinson’s disease. A small device that generates impulses is inserted in the chest wall and is connected with a fine wire placed under the skin that runs to the brain. The device releases tiny electric current that stimulates the parts of the brain that are affected by Parkinson’s disease. This may ease the symptoms but is not a complete cure.
Other surgical methods include pallidotomy (used in unilateral dyskinesia, severe 'on-off' fluctuations and drug failure), thalamic and Subthalamic surgery (for controlling tremors) etc.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)