Six Parkinson’s symptoms people don’t talk about

Parkinson’s is more than a tremor. From your head to your feet, Parkinson’s can affect all areas of the body. We take a look at some of the lesser known symptoms of the condition, and how research is helping to improve them.

Lynn Duffy
Apr 15 · 8 min read
J. Parkinson, An essay on the shaking palsy. Credit: Wellcome Collection. CC BY

Tremor or shaking, especially affecting the hands, is probably the most well known and obvious symptom of Parkinson’s. In fact, James Parkinson’s defining essay on the condition called it the “Shaking Palsy”.

But Parkinson’s is more than a tremor. In fact, people with Parkinson’s tell us that tremor is often the least of their problems.

What is Parkinson’s?

When we think of Parkinson’s, we think of dopamine cells in the brain being lost, leading to problems with movement. This is true, but it doesn’t cover everything that changes with the condition. Many different areas of the brain are affected. And this causes a number of different symptoms.

In fact, researchers think that the loss of dopamine-producing cells in the substantia nigra is one of the last regions of the brain to be affected in Parkinson’s.

Last year, we highlighted six lesser-known symptoms of Parkinson’s and the research that’s happening to help.

A year on, following the GDNF documentary, awareness of Parkinson’s has increased, but there’s still a long way to go. So in this new blog, we highlight six more symptoms (or medication side effects) of Parkinson’s that people just don’t talk about:

  1. Loss of smell

1. Loss of smell

Losing your sense of smell is often an early symptom of Parkinson’s, sometimes appearing years before the visible problems with movement develop. It’s also quite common — around 75% of people with Parkinson’s have a poorer sense of smell compared with people of the same age.

This strange symptom is thought to be caused by a build-up of clumps of a protein called alpha-synuclein in the area of the brain responsible for the sense of smell, known as the olfactory bulb.

What research is being done?

Researchers are investigating whether “scratch and sniff” tests can be used to improve diagnosis, helping to separate Parkinson’s from other similar conditions.

Being an early symptom of Parkinson’s, researchers are also hoping that loss of smell may allow researchers to identify people in the earliest stages of Parkinson’s, years before diagnosis.

2. Apathy

Described as a complete lack of motivation… or emotion… or passion — a feeling of total detachment — apathy can be a frightening symptom of Parkinson’s.

Although the research evidence is limited, studies suggest it may affect up to 70% of people with the condition.

The symptom is the result of having lower levels of dopamine in the reward pathways of the brain. When we anticipate a reward or danger, our brain cells release dopamine. This encourages us to act and get ready to move. In Parkinson’s, activity becomes more of an effort as there’s no longer the necessary ‘leg up’ from dopamine.

What research is being done?

We’re funding Dr Claire O’Callaghan at the University of Cambridge to find a treatment for apathy in Parkinson’s. She’s focusing on a hormone called noradrenaline, which we know can be lower in the brains of people with Parkinson’s.

Researchers think there’s a link between noradrenaline and feelings of motivation. So Claire is testing a drug called atomoxetine, which increases the levels of noradrenaline. She wants to establish if it could be used as a treatment to address poor motivation on a day-to-day basis in people with Parkinson’s.

3. Changes in eyesight

Our visual system is complicated, with many different cell types, muscles, and areas of the brain all working together to allow us to see the world around us.

In Parkinson’s, problems with eyesight are common.

Dopamine plays a key role in the retina of the eye. The retina is a layer of nerve cells that line the back wall inside the eye. When light hits the retina, nerve signals are sent from the eye into the processing areas of the brain, turning the light signals into an image we see. Dopamine-producing nerve cells in the retina help the eye adapt to changing light levels. In Parkinson’s, the loss of these dopamine-producing cells can make it harder for people to see different shades of colours, or to discriminate an object from its background.

In order to take in the full view of the world around us, our eyes need to be able to move, and sometimes quickly. It takes seven different muscles to control eye movement. And each of these muscles can be affected by Parkinson’s. For people with the condition, vision can be blurred, or a bit jerky. Double vision and dry eyes (caused by problems with blinking) are also common.

What research is being done?

They say the eyes are the window to the soul. More accurately, they are the window to the brain. Researchers can look at what’s happening in the eyes, and that gives them some clues about what’s going on in the brain.

Thinning of the retina, caused by loss of dopamine-producing cells, seems to happen early on in Parkinson’s. And it’s thought these changes might be linked to the loss of nerve cells in the substantia nigra, causing the movement problems.

This ‘biomarker’ for Parkinson’s gives researchers an opportunity to understand more about the early stages of the condition. As the retina is easy to image, scientists can quickly test drugs to see if they have an effect on the dopamine cells in the eye. If they do — it’s hoped they’ll also work in the other areas of the central nervous system affected by Parkinson’s.

4. Sleep

Problems with sleep are common in Parkinson’s. People report symptoms like insomnia, disturbed sleep, or excessive daytime sleepiness, all of which can have a dramatic impact on quality of life.

Sleep problems can be more common because of other Parkinson’s symptoms, such as tremor, stiffness, pain and restless legs syndrome, all of which can disturb sleep. And this can lead to daytime sleepiness.

But changes in the brain can also cause problems with sleeping — and may be one of the earliest symptoms of Parkinson’s. Researchers believe the loss of nerve cells in areas of the midbrain and lower brain stem can affect the sleep-wake cycle. You can read more about the early symptoms of Parkinson’s below.

What research is being done?

Evidence is mounting that one particular sleep problem may be one of the earliest symptoms of Parkinson’s, and could even help predict who will go on to develop the condition.

Rapid eye movement (REM)sleep behaviour disorder is a condition where people act out vivid dreams, often shouting out or thrashing around in their sleep. Research has uncovered a link between REM sleep disorder and an increased risk of Parkinson’s. It’s hoped that learning more about this symptom could help us to predict Parkinson’s or even diagnose it earlier.

We’re funding Professor Nicola Pavese and her team at Newcastle University to scan the brains of people affected by REM sleep behaviour disorder in the hope of identifying changes in the brain related to early-stage Parkinson’s. This study could help identify areas in the brain that could be targeted in future drug discovery research in Parkinson’s.

5. Hallucinations

Visual hallucinations — seeing something that doesn’t exist — can affect up to 74% of people living with Parkinson’s for 20 years or more.

Hallucinations and delusions usually happen in the later stages of Parkinson’s, most commonly as a side effect of the medication, rather than as a direct symptom. People with Parkinson’s take dopamine-based medication to help manage their symptoms. But too much dopamine in the brain can cause visual hallucinations.

Unfortunately, the usual treatment for hallucinations — anti-psychotics — can’t be used in Parkinson’s, as they work by reducing dopamine levels in the brain, risking movement problems getting worse.

What research is being done?

The hunt is on to find anti-psychotics that could be effective for treating hallucinations in Parkinson’s.

Pimavanserin has been specifically designed to treat hallucinations and delusions without worsening the motor symptoms of Parkinson’s. It works by blocking receptors that respond to serotonin in the brain, leaving the dopamine pathways untouched. Research published in 2017 showed that pimavanserin is particularly effective in treating Parkinson’s with dementia.

Unfortunately, though licensed in the USA, pimavanserin has not been granted a license here in the UK. We’re hoping this will change soon.

6. Involuntary movements

How the brain controls movement is complicated — a delicate balance of chemicals, all working together to allow the body to move as we want it to.

This balance is disrupted in Parkinson’s when dopamine levels are decreased. The current medical solution to this is quite crude — more dopamine is given in the form of levodopa to restore the balance. But when the medication is taken, the amount of dopamine in the brain can suddenly spike. This can overload the system, causing the unwanted side effect of dyskinesia — uncontrolled, often jerky movements.

Around half of all people with Parkinson’s will experience it after just 5 years of taking levodopa, and up to 80% of people will experience it after 10 years.

What research is being done?

The solution to too much dopamine may lie with another chemical entirely. Brain cells that produce the chemical serotonin can also interact with levodopa, turning it into dopamine and releasing it when they release serotonin. This leads to a loss of control of dopamine signalling.

Drugs that trick serotonin cells into thinking they are releasing too much serotonin could be the answer as it would slow the release of both dopamine and serotonin.

The Parkinson’s Virtual Biotech invested in a drug called NLX-112, which targets the serotonin receptors in the brain. The study was a success and NLX-112 can now go forward into phase 2 clinical trials testing to see if it can treat Parkinson’s-related dyskinesia.

Join us!

It’s vital that people affected by Parkinson’s are involved in research — helping to set the priorities, shape the questions and find the answers to problems like those highlighted in this blog.

Parkinson’s UK

Get the latest research news, discover more about Parkinson’s and read about how others are getting involved. For information and support, visit

Thanks to Dr Beckie Port

Lynn Duffy

Written by

Scientific copy writer @ParkinsonsUK. Lover of tea. Views are my own

Parkinson’s UK

Get the latest research news, discover more about Parkinson’s and read about how others are getting involved. For information and support, visit

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