Parkinson's Disease

Parkinson's Disease is named after Dr. James Parkinson 1755-1824), the London doctor whose essay on the Shaking Palsy was published in 1817. James Parkinson established the condition as a clinical entity and his essay continues to be recognised through the world as the classic description of the condition.

Parkinson's Disease is a progressive neurological disorder affecting learned voluntary movements such as walking, talking, writing and swallowing. There are three main symptoms: tremor, rigidity and bradykinesia (slowness of movement). However, not everyone will experience all three symptoms. The symptoms of Parkinson's are caused by a shortage of a chemical messenger (dopamine) in the basal ganglia, the part of the brain which controls movement.

The basal ganglia behave rather like the floppy disk of a computer where programs of movements are stored and adjusted. Dopamine working in balance with another chemical messenger, acetylcholine, is responsible for the feedback mechanism that enables these programs of movement to be put into action and ensures smoothness and control of movements. With Parkinson's this balance is upset, resulting in stiffness in the muscles, slowness, difficulty when starting movements, and in some people, tremor.

The symptoms of Parkinson's do not appear until about 80% of the dopamine has been lost, and the level of dopamine will continue to fall slowly over many years, causing the condition to progress. However each person is very different and the rate and progression of the condition will vary enormously from one person to another.

The incidence of Parkinson's Disease is approximately 1:1000 in the general population, rising to 1:100 over the age 65 and 1:50 over the age of 80. A little recognised fact is that 1:20 people diagnosed is aged under 40. There are more than 120,000 people with Parkinson's Disease in the United Kingdom today and it is common in all parts of the world.

The main treatment for Parkinson's Disease is drug therapy. Because no two people with Parkinson's Disease are exactly alike, the drug treatment has to be tailored to the individual and the timing of medication is as important as the dosage. With the optimum drug treatment, life expectancy for Parkinson's Disease is normal. Management plays a very important part in the care of people with Parkinson's Disease and professions such as physiotherapy and speech therapy have an important role to play. (Help for carers is also vitally important).

Drug Therapy
Although at present there is no cure, several different drug treatments are available to help control the symptoms of Parkinson's. The main aim of drug therapy in the treatment of Parkinson's is to restore dopaminergic function in the brain. This can be achieved by increasing the level of dopamine (levodopa drugs), blocking the action of acetylcholine (anticholinergics) or by using drugs which mimic the effects of dopamine (dopamine agonists).

Levodopa is the most commonly used drug to treat Parkinson's. Unfortunately the long-term treatment of Parkinson's with levodopa is often complicated by the development of a fluctuating response to drug doses. These fluctuations, which are often called "wearing off" (where an adequate dose of levodopa does not last as long as initially expected and Parkinson's symptoms recur) or the "on/off' syndrome (disabling fluctuations in ability), generally occur after about 5-10 years of levodopa treatment. Some people have likened the "on/off""' syndrome to the idea of a light being switched on or off- "off'" when there is no response to the drugs and "on" when the drugs are effective.

The benefits of levodopa can be improved by prescribing them with other drugs such as dopamine agonists or COMT inhibitors. These drugs can also sometimes be used to help treat people on levodopa who are experiencing fluctuations.

COMT Inhibitors
The body produces an enzyme called catechol-O-methyl transferase (COMT) which breaks down levodopa. COMT inhibitors are a new type of drug which work by blocking this enzyme and as a result slow the destruction of levodopa in the body. COMT inhibitors are therefore prescribed to be used with levodopa to extend or improve the benefits of levodopa and thus reduce the symptoms of Parkinson's.