What Is Parkinson's Disease


Parkinson’s disease (PD) is the second most prevalent  neurodegenerative disease globally, following Alzheimer’s disease.1  The disorder is currently estimated to affect 8.5 million individuals, however, its prevalence is expected to increase to 13 million by 2040, alongside our ageing population.  

PD is a progressive neurological condition, which causes damage to the nerve cells, especially in an area of the brain called the substantia nigra,3 over-time this contributes to the physical and cognitive dysfunction observed in PD. PD largely affects the dopaminergic neurons found in  the substantia nigra.3 This brain region is responsible for our voluntary movements, so the degeneration of dopaminergic neurones plays a fundamental role in the development of PD symptoms. 

Read on to learn more about the causes, symptoms and treatments of PD. 

How does Parkinson’s progress?

PD's progression is unpredictable, and how the symptoms present themselves will differ for everyone. However, it can be helpful to understand the stages of PD typically observed. 

​​Parkinson’s disease can be categorised into three different phases:5

  • The Preclinical phase: Eurodegeneration of dopmainergic neurones has begun, but there is no evidence of clinical symptoms. This can occur decades before any symptoms manifest4
  • The Prodromal phase: Some clinicla symptoms have emerged, however, they are not enough for a clinical diagnosis of PD
  • The Clinical phase: Parkinsonian symptoms are clearly evident and clinicians are able to make a diagnosis of PD

Alternatively, PD can be classified into five stages that clinicians can use to track the progression of motor symptoms.

  • Stage One: Mild symptoms are present but do not interfere with the individual’s daily life. Symptoms usually only affect one side of the body in this early stage
  • Stage Two: Symptoms worsen and start to affect motor functions on both sides of the body. The severity of symptoms means that individuals can still carry out daily tasks by themselves
  • Stage Three: A key symptom that presents itself in this stage is a loss of balance. Other motor symptoms continue to worsen, and the disability is considered mild to moderate in severity. Individuals can still live independently but may be somewhat restricted
  • Stage Four: This marks when symptoms have become fully developed and the disability is considered severe. Individuals are unable to live independently
  • Stage Five: This is considered the advanced stage of the disease and occurs when the individual requires full-time care and assistance. The severity of symptoms such as muscle stiffness and other motor issues mean the individual cannot walk or even stand. At this stage the individual requires 24-hour assistance and care

Causes of Parkinson's disease

PD is caused by the degeneration of dopaminergic neurons in a part of the brain called the substantia nigra.6 This degeneration is caused by the presence of alpha-synuclein-containing Lewy bodies in neurones leading to neuronal death.  This causes the brain to function atypically and can manifest as increased involuntary movements.

The death of dopaminergic neurones in the substantia nigra results in the amount of dopamine in the brain being reduced. This can result in symptoms such as slowed movements. 

But what triggers the degeneration of dopaminergic neurones in the substantia nigra? 

The reason for the degeneration of dopaminergic neurones is not currently well understood. Research indicates that a combination of genetic and environmental factors may be responsible. 

  1. Genetic. While the exact cut It is very rare for Parkinson’s to run in families, however, research estimates that 5-10% of cases involve some genetic component7

Genetic risk factors that have been identified by researchers include: 

  1. Environmental. There is some evidence that environmental factors may cause PD. Some environmental risk factors that have been identified are listed below: 
    • Exposure to pesticides and herbicides may contribute to PD
    • Traumatic brain injury6
    • Pathogens: bacterial or viral6
    •  History of melanoma6

Signs and symptoms of parkinson's disease

The symptoms associated with PD typically appear gradually when an estimated 50% of dopaminergic neurones in the substantia nigra have been lost.  However, the severity and the order these symptoms develop differ greatly between individuals. This means there is no ‘typical’ Parkinson’s patient. 

Parkinson’s disease is defined by its three cardinal motor features:7 

  • Bradykinesia (slowness in movements)
  • Resting tremor 
  • Rigidity 

While Parkinson’s disease is often considered a movement disorder, it causes other physical  and cognitive symptoms. The non-motor symptoms are often the first to develop during a period called the prodromal phase.1

Physical symptoms include: 

Cognitive symptoms:

Diagnosis of parkinson's disease

If you suspect that you may have Parkinson’s symptoms it is important that you seek medical attention. If your GP suspects that your symptoms may be a result of PD you will be referred to a speicalist. 

The specialist will ask you to perform a series of physical exercises which help them to assess if you are displaying the motor-based symptoms of PD. Brain scans can also be carried out to eliminate other explanations for your symptoms. Non-motor symptoms are also taken into account as supporting evidence. 

Management and treatment options for parkinson's disease

Unfortunately, there is currently no cure for PD, instead treatment focuses on helping individuals manage their symptoms and improve their quality of life.

The medication used to manage the symptoms of PD differ depending on the individual. The main types of medication used by clinicians are:

  • Levodopa6 The use of levodopa increases the level of dopamine, which can help to improve movement problems. An increased levodopa dose over time is normal. Unfortunately, Levodopa is associated with some side effects such as dyskinesias.
  • Dopamine agonists Dopamine agonists can be used at the same time as levodopa, so that a smaller dose of levodopa can be administered. Dopamine agonists are also associated with some serious side effects such as hallucinations, increased confusion and the development of compulsive behaviours
  • COMT inhibitors are often prescribed at an advanced stage of PD. They prevent the breakdown of levodopa by COMT6
  • MAO-B inhibitors are often prescribed during advanced stages of PD. They work by preventing the breakdown of dopamine in the brain6

In addition to medications, there is supportive care such as physiotherapy or occupational therapy that can help individuals with PD manage their symptoms on a day-day basis. For some, surgery may be an option. A type of surgery called deep brain stimulation can be used. 

A specialist in PD will be able to help you make an informed decision about which treatment option is best for you. 


Can parkinson's disease be prevented

Parkinson’s disease cannot be prevented but some studies have highlighted factors that appear to reduce the risk of developing the disease, including:

Importantly, these are only based on association-based studies and do not necessarily prevent the disease. 

Who are at risks of Parkinson's disease

The risk of Parkinson’s disease increases with age and peaks at approximately 80 years,1 with 65-70 years being the average age for the onset of the disease.7 Parkinson’s affects slightly more men than women, but the disease appears to progress more rapidly in women.3 Other factors that may increase your risk of Parkinson’s include exposure to pesticides, a history of melanoma, and traumatic brain injuries.1

How common is Parkinson's disease

It is estimated that Parkinson’s affects 100-200 individuals per 100,000.7

What can I expect if I have Parkinson's disease

Most people, once diagnosed, respond well to treatment and are expected to have a normal life expectancy. Someone with Parkinson’s disease can expect the symptoms to progressively worsen over time . You might not develop all the symptoms listed above, and those you experience may differ in their severity. You may need regular check-ups to help monitor the progression of the disease and how you’re responding to any treatments. 

When should I see a doctor

You should see a doctor if you are experiencing any of the signs and symptoms of the disease. 


Parkinson’s disease is a progressive neurodegenerative disease that affects the substantia nigra, the part of the brain that controls our voluntary movements. Because of this, it is largely thought of as a movement disorder, but there are many non-motor symptoms that also result from the disease. Advances in treatments now mean that many people can manage their symptoms and have a great quality of life. While it largely affects individuals 65 years and older, at any age, if you think you might be experiencing any of the signs and symptoms, you should see a doctor. 


  1. Ascherio A, Schwarzschild MA. The epidemiology of Parkinson’s disease: risk factors and prevention. Lancet Neurol. 2016 Nov;15(12):1257–72. https://pubmed.ncbi.nlm.nih.gov/27751556/
  2. Launch of WHO’s Parkinson disease technical brief [Internet]. [cited 2023 Apr 7]. Available from: https://www.who.int/news/item/14-06-2022-launch-of-who-s-parkinson-disease-technical-brief
  3. Cerri S, Mus L, Blandini F. Parkinson’s disease in women and men: what’s the difference? JPD [Internet]. 2019 Jul 30 [cited 2023 Apr 7];9(3):501–15. Available from: https://www.medra.org/servlet/aliasResolver?alias=iospress&doi=10.3233/JPD-191683
  4. Pajares M, I Rojo A, Manda G, Boscá L, Cuadrado A. Inflammation in parkinson’s disease: mechanisms and therapeutic implications. Cells. 2020 Jul 14;9(7):1687. https://pubmed.ncbi.nlm.nih.gov/32674367/
  5. Stages of parkinson’s | parkinson’s foundation [Internet]. [cited 2023 Apr 7]. Available from: https://www.parkinson.org/understanding-parkinsons/what-is-parkinsons/stages
  6. Jankovic J, Tan EK. Parkinson’s disease: etiopathogenesis and treatment. J Neurol Neurosurg Psychiatry [Internet]. 2020 Aug [cited 2023 Apr 7];91(8):795–808. Available from: https://jnnp.bmj.com/lookup/doi/10.1136/jnnp-2019-322338
  7. Tysnes OB, Storstein A. Epidemiology of Parkinson’s disease. J Neural Transm [Internet]. 2017 Aug [cited 2023 Apr 7];124(8):901–5. Available from: http://link.springer.com/10.1007/s00702-017-1686-y
  8. Parkinson’s disease [Internet]. nhs.uk. 2017 [cited 2023 Apr 7]. Available from: https://www.nhs.uk/conditions/parkinsons-disease/
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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