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What is Parkinson’s disease?

Parkinson’s disease (PD) is a chronic, progressive movement disorder causing nerve cells (neurons) that are essential for normal movement and coordination to stop working properly.

These neurons communicate with each other by producing a chemical messenger called dopamine. Loss of dopamine leads to the symptoms of PD.

Parkinson’s disease affects over six million people worldwide [1].

The exact causes are unknown but 10-25% of people have a history of PD in the family [2,3].

For a diagnosis of PD to be considered, patients must experience at least two movement symptoms. These symptoms must include bradykinesia in conjunction with rigidity, rest tremor, or both [4], described further in Table 1.


Core motor symptoms

  • Slow/reduced movement, mask-like facial expression, less blinking
  • Difficulty performing repetitve movements
  • Short, shuffling steps
  • Soft speech
Rest tremor
  • One-sided (usually) slow tremor of forearm/hand/finger
  • Sometimes in leg
  • Tremor disappears when limb is used
  • Can worsen with stress
  • Muscles are stiff, causing less mobile joints, especially neck/shoulders
  • Reduced arm swing when walking
  • Can be painful

Gait “freezing” when about to take a first step or change direction, and tendency to fall backwards are also symptoms.

Because PD is an expression of reduced dopamine, and accumulation of abnormal protein “Lewy bodies” in the brain, non-motor symptoms can occur. These may precede motor symptoms by years (called “prodromal PD”) e.g. [2,3]:

  • Loss of sense of smell/taste
  • Sleep problems including vivid dreams
  • Constipation
  • Erectile dysfunction
  • Cognitive problems including dementia
  • Hallucinations.

There is no definitive test for PD, so history, examination and symptom assessments are carried out by a neurologist specialising in Parkinson’s disease [5].

Although there is no cure or way to slow its course, there are many treatments available, including:

  • Diet and exercise
  • Medications
  • Neurosurgery.

Diet and exercise

A healthy diet is recommended, avoiding too much fat or protein which can affect medication absorption.

For constipation, increased fluid and fibre is recommended, and sometimes laxatives and/or exercise.

If swallowing is a problem, a swallowing assessment and advice including thickened fluids or softer diet may be needed.

Exercise should be tailored to the person’s needs and wishes. This might include falls and balance training, stretching, strengthening, aerobic exercise, or tai chi.


The different drug classes work in diverse ways. Levodopa or dopamine agonists are typically used first as they are most effective. Table 2 summarises commonly used drugs.


Common drug treatments for Parkinson’s disease

Drug class Benefits

Levodopa prescribed in combination pill with:

  • carbidopa (to reduce side effects)
  • benserazid

Increases brain dopamine levels

Dopamine agonists e.g. pramipexole, rotigotine, ropinirole, apomorphine

Mimics action of dopamine

Catechol-O-methyltransferase inhibitor (COMT inhibitor) e.g. entacapone

Prolongs Levadopa effect

Monoamine oxidase type B inhibitors (MAO-B inhibitors) e.g. selegeline, rasaglin

Blocks Levadopa breakdown

Anticholinergics e.g. benztropine, trihexyphenidyl

Reduce activity of chemical messenger, acetylcholine

Reduces tremor

N-methyl-D-aspartate (NMDA) receptor antagonist – amantadine

Reduces dyskinesia (see limitations of PD treatments”)

Limitations of Parkinson’s disease drug treatments

As well as needing to take medications, often multiple times daily, after five years most people experience complications, such as [7]:

  • Dyskinesia – involuntary writhing movements
  • Wearing-off – occurs when a dose is running out, leading to motor or non-motor symptoms. Can be unpredictable and severe to point of “freezing”
  • Constipation
  • Erectile dysfunction
  • Impulse control disorders – may occur due to certain PD medications, such as compulsive gambling, overspending, hypersexuality


Since 1993, deep brain stimulation (DBS) has been an effective alternative treatment for thousands of patients whose advanced PD is no longer responding to medications. One or more electrodes are surgically implanted into specific areas of the brain. The electrodes modulate abnormal patterns of brain activity, via a connected electrical impulse generator under the skin of the chest. After implantation, location, size, strength, and the shape of the stimulating electric field can be adjusted at clinic reviews. However, this classic “open-loop” system does not enable automatic changes in electrical impulse generation from patient feedback, which is a problem in a disease which often fluctuates as well as progresses [7].

Benefits of DBS can vary depending on where the electrodes are implanted, with improvements reported in rigidity, bradykinesia, tremor, dyskinesia, “wearing-off” time and quality of life [7]. However, problems include [7]:

  • Improved gait and balance may be difficult to achieve
  • Some patients experience speech or mood problems
  • Patients must be awake during surgery to provide feedback to their surgeons
  • Errors in electrode placement can result in side effects or ineffective therapy

Surgery where part of the brain is removed under the guidance of scans may be an option for some patients.

Medical disclaimer

This article contains general information relating to a medical condition. Such information is provided for informational purposes only and does not replace medical advice given by your healthcare professional.


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2. Parkinson’s Foundation. A Guide to Parkinson’s Disease [Internet]. 2018. p. 1–50. Available from:

3. Lee TK, Yankee EL. A review on Parkinson’s disease treatment. (CC BY 4.0). Neuroimmunol Neuroinflammation [Internet]. 2021 Dec 21 [cited 2022 Feb 20];8:222–44. Available from:

4. Postuma RB, Berg D, Stern M, Poewe W, Olanow CW, Oertel W, et al. MDS clinical diagnostic criteria for Parkinson’s disease. Mov Disord [Internet]. 2015 Oct 1 [cited 2022 Feb 20];30(12):1591–601. Available from:

5. Marsili L, Rizzo G, Colosimo C. Diagnostic criteria for Parkinson’s disease: From James Parkinson to the concept of prodromal disease. (CC BY). Front Neurol [Internet]. 2018 Mar 23 [cited 2022 Feb 20];9:156. Available from:

6. Mudiyanselage SB, Watts JJ, Abimanyi-Ochom J, Al. E. Cost of Living with Parkinson’s Disease over 12 Months in Australia: A Prospective Cohort Study. (CC BY). 2017;1–13. Available from: chrome-extension://dagcmkpagjlhakfdhnbomgmjdpkdklff/enhanced-reader.html?

7. Hickey P, Stacy M. Deep brain stimulation: A paradigm shifting approach to treat Parkinson’s disease. (CC BY). Front Neurosci. 2016 Apr 28;10(APR):173.

8. Bionics Institute. 2019– 2020 Annual report [Internet]. 2020. Available from: