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Often-ignored hallucinations may be an early warning of Parkinson’s and cognitive decline. Image credit: Bárbara Tamura/Stocksy.
  • New research suggests that people diagnosed with Parkinson’s disease who have hallucinations early on face a greater risk of rapid cognitive decline.
  • However, minor hallucinations often go underreported and ignored by Parkinson’s disease patients and clinicians.
  • European experts ran a long-term study that tied Parkinson’s disease and early hallucinations to “a stronger decline in frontal-subcortical functions.”
  • Experts encourage anyone with Parkinson’s disease who has hallucinations to inform their healthcare provider promptly.

Parkinson’s disease (PD) and related neurodegenerative diseases are often far advanced before diagnosis. This severely limits prevention and treatment options.

Parkinson’s disease has long been regarded primarily as a movement disorder. However, growing research points to impaired executive function as a major factor in its progression.

European researchers may have found a novel way to determine the early onset of Parkinson’s disease and related cognitive decline by observing cognitive and psychiatric symptoms.

Experts at the Swiss Federal Institute of Technology (EPFL) in Switzerland and Sant Pau Hospital in Barcelona, Spain, found that people with Parkinson’s disease and early hallucinations may lose executive function more rapidly.

Their study appears in Nature Mental Health.

Hallucinations are false sensations of things that are not present.

People with Parkinson’s disease may experience one or several types of hallucinations involving, sight, hearing, touch, smell, or taste.

Scientists already understand that complex visual hallucinations can be a marker of cognitive decline in Parkinson’s disease and related neurological conditions.

However, these kinds of hallucinations tend to occur at a later stage of the disorder, which rules out using them as early Parkinson’s disease markers.

Minor hallucinations happen in the early stages of Parkinson’s disease, but current research has not yet confirmed their relationship with cognitive impairment.

They can present before more common motor symptoms of Parkinson’s disease, such as trembling, rigidity, and bradykinesia.

What are minor hallucinations?

There are three main types of minor hallucinations:

  • Presence hallucinations — intense perceptions of the presence of someone who is not there.
  • Passage hallucinations — cause a person to think they see someone or something passing in their peripheral visual field.
  • Pareidolias — cause someone to think they see a face or object in formless or patterned visual stimuli such as clouds or a carpet.

In this joint study between EPFL and Sant Pau Hospital, researchers gathered data on 75 people with a Parkinson’s disease diagnosis. The patients were around 60 to 70 years of age.

The team investigated whether individuals with Parkinson’s disease who experienced minor hallucinations might ”show altered brain oscillations and whether such minor hallucinations-related […] changes are associated with cognitive impairments that increase over time.”

The study participants undertook psychiatric interviews to determine whether they were experiencing minor hallucinations. They also underwent neuropsychological testing to measure cognitive function.

The researchers collected electroencephalography (EEG) data as well.

Follow-up neuropsychological tests took place 2 years later with 68 patients and five years later with 54 patients.

Dr. Bernasconi and his colleagues observed that frontal theta oscillations in Parkinson’s disease patients with minor hallucinations correlated with reduced cognitive frontal-subcortical functions. Doctors believe that frontal-subcortical deficits are an indicator of cognitive impairment.

They noticed that the results of the neuropsychological tests were similar among the patients with and without minor hallucinations. This confirmed that neuropsychology alone is not enough to detect minor hallucinations-related changes.

A 5-year follow-up confirmed the oscillations and showed a more pronounced decline in frontal-subcortical functions in the individuals who had reported minor hallucinations at the study outset.

Neurosurgeon Dr. Gurneet Singh Sawhney from Neurolife in Mumbai, India, not involved in the research, remarked to Medical News Today that the study’s conclusion makes “an important finding as it highlights the need for neurologists to monitor their Parkinson’s disease patients closely for signs of cognitive impairment.”

Dr. Sawhney explained why the researchers are investigating the correlation between electrophysiological measures of theta oscillations and clinical symptoms of hallucinations.

He noted: “Theta oscillations are electrical signals in the brain, typically measured by EEG scans, that have been linked with various cognitive processes such as decision making and working memory. […] Parkinson’s disease patients often exhibit decreased theta activity in the frontal lobe, which is associated with impaired executive functions such as working memory and decision making.”

MNT asked the study’s lead author, Dr. Fosco Bernasconi, of EPFL’s Laboratory of Cognitive Neuroscience, about other procedures under consideration for detecting Parkinson’s disease early.

He replied that robotic technology and virtual reality have allowed him and fellow researchers to analyze and quantify hallucinations safely. However, the unpredictable, subjective nature of hallucinations makes them challenging to study.

He said: “We are currently further developing our methods and will start testing our approach to assessing whether we can identify individuals with Parkinson’s disease who may develop hallucinations in the future.”

Dr. Bernasconi noted that these tests are still in their early phases and will require continued follow-up with patients.

Hallucinations may happen regularly in at least one out of two people with Parkinson’s disease. However, many people do not acknowledge or discuss them as symptoms of Parkinson’s disease with their healthcare professionals. Dr. Bernasconi told MNT that “this is often due to a fear of stigma.”

“In addition,“ he further shared, “the so-called ‘minor’ hallucinations, which include presence hallucinations — the sensation that someone is behind the individual experiencing the hallucination, but no one is there — might be not always disturbing or distressing for the individual experiencing it and is usually associated with neutral and sometimes positive emotional sensations.”

If the experience is not unpleasant, the lead author said, a person is not likely to report symptoms to their healthcare provider.

In the meantime, the study authors hope their work alerts people to the urgency of disclosing the occurrence of early hallucinations.

“We believe that it is important to make individuals aware that such hallucinations are part of the disease and that it’s important to share those symptoms with health professionals and family,” said Dr. Bernasconi.

Dr. Sawhney also emphasized that:

“It is […] essential for neurologists to monitor the electrophysiological measures of their patients, particularly those suffering from Parkinson’s disease, to detect any signs of cognitive impairment or decline.”

“Usually, individuals with Parkinson’s disease are mostly followed by movement specialists. To have a global view of the symptoms affecting the patient, we believe that it is important that they also assess systematically the presence of non-motor symptoms, especially those that might be related to changes in cognitive functions, such as ‘minor’ and complex [visual] hallucinations,” Dr. Bernasconi further noted.