Presence Hallucinations as an Early Indicator of Cognitive Decline in Parkinson’s Disease

Parkinson’s disease (PD) psychosis, which includes hallucinations and delusions, can frequently occur as PD advances. Hallucinations involve seeing, hearing, experiencing or sensing things that are not there. Delusions are false beliefs that are not based in reality, such as thinking that someone is stealing from you or that your spouse is cheating on you. In PD, psychosis is a known risk factor for cognitive decline and cognitive decline is a risk factor for hallucinations.

Although psychosis is usually a symptom of advanced disease, earlier on in the disease people with PD might have experiences that can be considered minor hallucinations. One such sensation is called presence hallucinations, in which a person has a feeling that someone is standing near them, but when they turn to look, there is no one there.

A recent paper studied 75 people with PD who did not have dementia but did have minor hallucinations. EEGs were performed on the participants and results showed that those with minor hallucinations exhibited a feature called enhanced frontal theta oscillations. These patients were followed over time and at a five year follow up, neuropsychological testing showed an increased decline in cognitive function among those who had initially experienced minor hallucinations vs those who did not. Taken together, these results suggest that minor hallucinations as a clinical feature and enhanced frontal theta oscillations on EEG could both be early biomarkers of cognitive decline in PD.

These findings warrant further study, but in the meantime, if you think you are experiencing minor hallucinations, bring them to the attention of your neurologist.