Explainer: what is Parkinson's disease?Claire Stevens, Neuroscience Research Australia
Parkinson’s disease was not always known by this name. Almost 200 years ago in 1817, when English doctor James Parkinson first described the disease, he called it Shaking Palsy. But Parkinson’s disease affects much more than just movement.
There are good reasons for why we think of this illness as largely affecting movement. Consider the actor Michael J. Fox and boxer Muhammad Ali. We know that they have Parkinson’s because of the obvious shaking in their limbs. This shaking or tremor is known as one of the four cardinal motor symptoms of Parkinson’s, but there’s much more to the illness.
Parkinson’s is a complicated and devastating disorder that currently doesn’t have a cure. But the good news is that scientists have recently taken some promising steps towards one.
Prevalence, causes and medication
Today, there are around 6.3 million people living with Parkinson’s worldwide, and approximately 80 000 of these people reside in Australia. By 2030, it’s estimated the total number of people affected by this disease will have risen to eight million due to the ageing population.
Parkinson’s affects both males and females, although males have a slightly higher risk of developing the disease. Most people are aged between 55 and 65 years when they are diagnosed, but you can be affected at any age.
The first symptoms are often trembling or shaking in one hand when it is at rest, or muscle stiffness in the limbs or whole body. But people without Parkinson’s may also experience similar symptoms so don’t jump to conclusions. Only neurologists who specialise in Parkinson’s have the expertise to diagnose the disease.
Approximately one in ten people with Parkinson’s have a family history of the disease, but the cause is not known for the other 90%. What we do know is that people with Parkinson’s slowly lose cells called neurons in a region of the brain called the substantia nigra.
Neurons in the substantia nigra produce a chemical known as dopamine, which is responsible for movement. When these neurons die, there’s not enough dopamine in the brain and this causes the four cardinal motor symptoms – tremor, slow movements, stiffness and loss of balance.
People with Parkinson’s disease can be given a number of drugs that replace the lost dopamine in the brain to improve movement. The gold standard of these drugs is called levodopa and may be given alone or in combination with other drugs. Unfortunately, medications of this kind have severe and disabling side effects including nausea, vomiting, constipation and dyskinesias (involuntary movements).
Over time, the drugs become less effective for controlling motor symptoms and patients must take higher doses more frequently to get the same benefit.
What most people don’t realise is that Parkinson’s patients also suffer from a range of other symptoms unrelated to movement. These are commonly called non-motor symptoms and include loss of smell, anxiety, depression, impotence, fatigue, loss of motivation, sleep disturbances, hallucinations and dementia.
These symptoms are often ignored, but they’re very common and can significantly affect quality of life.
Research at Neuroscience Research Australia is looking at the role of inflammation in the brains of people with Parkinson’s disease.
Cells called glia produce inflammation in the brain. Glia are very important because they perform a number of tasks that support and protect neurons from harm, including releasing chemicals that cause inflammation. But in those suffering from Parkinson’s, it’s thought the glia may be responsible for progression of the disease by releasing an excess of inflammatory chemicals that cause the destruction of neurons.
In a review article published in the journal Movement Disorders, Professor Glenda Halliday and I propose that glia are not only involved in the progression but also at the very earliest stages of Parkinson’s disease.
During these early stages, neurons are still alive and the motor symptoms of Parkinson’s are not yet present. We think scientists must understand the causes of the early changes in glia to successfully prevent neurons from dying.
This work is supported by findings showing that people who take the anti-inflammatory drug ibuprofen at least twice a week, are less likely to develop Parkinson’s disease.
This is exciting because it might mean that ibuprofen protects the brain by reducing inflammation – but there are other possible explanations as well. And it also doesn’t mean that people should immediately start consuming the drug because if taken regularly, ibuprofen can have severe side effects, such as gastrointestinal bleeding and an increased risk of heart attack and stroke.
More research is needed to fully understand what this finding means for Parkinson’s patients.
People suffering from Parkinson’s must endure a spectrum of symptoms ranging from motor problems, such as tremor and stiffness, to the less-recognised non-motor problems, such as dementia and hallucinations.
Although medications are available to treat some of these symptoms, they have severe and disabling side effects. It’s critical that scientists researching this disease concentrate their efforts on developing new treatments to improve the quality of sufferers' lives and lead us closer to finding a cure.