LONDON - Thinking that somebody is standing behind you when they’re not could be an early sign of Parkinson’s disease, a new study has suggested.

Experiencing a strong sensation that a person is behind you, when no one really is, is known as a ‘presence hallucination’, which could be a frequent but under-reported predictor of the condition.

While patients may ignore strange experiences and pass them off as a side effect of medication, researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, warned they appear in a third of Parkinson’s patients before the onset of trembling and other motor symptoms typically associated with the brain disease that worsens over time.

Once the motor symptoms have started, hallucinations affect half of all patients.

Writing in Nature Mental Health, experts discovered patients recently diagnosed with the disease who experience the hallucinations are more likely to have a rapid cognitive decline.

The disease is traditionally defined as a movement disorder, with typical motor symptoms including resting tremor, rigidity and slow movements, but it also leads to a wide variety of non-motor symptoms.

By focussing on early signs like hallucinations, the team hope to challenge the current reality that Parkinson’s is often diagnosed too late, limiting the availability of successful preventative and disease-modifying therapies.

Michael J. Fox, 61, recently shared the story behind his ongoing health battle with the condition in a Netflix documentary.

He was first diagnosed with early onset Parkinson's in 1991, dealing with it privately to begin with, but eventually the father-of-four found peace in going public.

He officially retired in 2020 after struggling to learn lines – though thus far exceeded the timeline doctors had originally given him.

Despite his acceptance of his diagnosis, he said honestly: "Parkinson’s is still kicking my ass. I won’t win at this. I will lose." But, he added, "There’s plenty to be gained in the loss."

The actor recently experienced a fall on stage at a fan event, prompting him to admit he was in "intense pain" due to his condition.

Other celebrities who have spoken about living with Parkinson's disease include Jeremy Paxman, Ozzy Osbourne and Billy Connolly.

What is Parkinson's disease?

Parkinson's disease is a condition where parts of the brain become progressively damaged over many years, explains the NHS website.

It is caused by a loss of nerve cells in the substantia nigra (a part of the brain), which leads to a reduction in dopamine (known as one of the 'happy hormones').

More specifically, dopamine also helps to regulate the movement of the body, with a lack of it responsible for many of the symptoms of the disease.

Who is most at risk of Parkinson's disease?

It is unclear exactly what causes the loss of nerve cells that leads to Parkinson's, but many experts think it is a result of a combination of genetic and environmental factors.

While Parkinson's can run in families due to 'faulty genes' being passed on by a parent, it is rare for it to be inherited this way.

Parkinson's disease affects roughly one in 500 people, according to the NHS. Most people with the condition start to develop symptoms when they're over 50. That said, around one in 20 people also first experience symptoms when they're under 40.

Men are slightly more likely to get the disease than women.

Parkinson's disease symptoms

There are three main symptoms of Parkinson's, which are:

- involuntary shaking of particular parts of the body (known as a tremor)

- slow movement

- stiff and inflexible muscles

Someone with Parkinson's disease can also experience a variety of other physical and psychological symptoms, including:

- depression and anxiety

- balance problems (this may increase the chances of a fall, which could help to explain Paxman's accident, for example)

- loss of smell (known as anosmia)

- sleeping problems (insomnia)

- memory problems.

The 'Parkinson's mask' – previously referred to by Paxman – is known as 'facial masking' or 'hypomimia', which links to the stiffness of muscles some people experience.

Nurse Linda, from the Parkinson's UK helpline, explains on the charity's website that the lack of dopamine in the brain can stop your facial muscles from working how they used to.

When this happens, people can look like they have a blank expression, even if they are experiencing a strong emotion. Having a Parkinson's mask is a common symptom and it doesn't mean someone with the condition is necessarily feeling low or depressed – they just can't use their facial muscles to correctly express themselves.

Many people with Parkinson's also report problems with apathy (lack of interest) and motivation, which means they might not respond to emotions like they used to.
Man speaking to doctor