Hallucinations, Illusions, and Delusions: What’s the Difference?

Experts explain the nuances between these symptoms of psychosis and what it means for someone with Parkinson’s.

by Judy Koutsky Health Writer

If you have a loved one with Parkinson’s, you may be familiar with some of the mild symptoms of psychosis. It can start with confusion and lead to seeing things that aren’t there or believing things that are not true. We asked the experts to explain the difference between hallucination, illusions, and delusions and what it means for someone with Parkinson’s disease psychosis. Here’s what they had to say.

Parkinson’s Disease Psychosis (PDP), in a Nutshell

Parkinson’s affects the central nervous system and the results are tremors, slow movement, stiffness, and loss of balance. Sometimes, psychosis or other cognitive changes can develop along with the physical ones. “Psychosis can be defined in two ways: a symptom of a medical condition characterized by a loss of contact with reality; or a psychiatric disorder that produces psychotic symptoms,” says Michael Okun, M.D., chair of neurology and executive director at the Norman Fixel Institute for Neurological Diseases at University of Florida Health in Gainesville. In most PD cases, psychosis occurs as a side effect of the disease and medications. Dr. Okun explains that 20% to 40% of people with Parkinson’s experience hallucinations, illusions, or delusions. But these three cognitive disturbances are not one and the same.

What Are Hallucinations?

The term “hallucination” describes something you see, hear, smell, taste, or feel that is not actually there, explains Dr. Okun. Hallucinations are not dreams or nightmares. They happen when you are awake and can occur at any time of day or night. “Some kinds of hallucinations can be felt (tactile), smelled (olfactory), or tasted (gustatory), but they are less common than visual hallucinations in Parkinson’s disease-associated psychosis.” One example? Someone has a hallucination that an insect or animal is crawling on them, but there's really nothing there, says Dev Patel, M.D., a psychiatrist who practices virtually at TeleMed2U.

What Are Illusions?

Illusions are another sensory misperception, but instead of seeing things that are not there (like hallucinations), people with illusions misinterpret real external stimuli. “In other words, they see or hear something wrong, such as mistaking hats on a coat rack for heads or hearing a chant instead of the air conditioner,” says Dr. Okun. Illusions tend to be less common in Parkinson's disease psychosis.

What Are Delusions?

Delusions are false, fixed, idiosyncratic beliefs. “They are not deliberate, cannot be controlled and are very real to the person with Parkinson’s,” says Dr. Okun. Delusions are ongoing and can be subtle. They often begin as generalized confusion at night and progress from there. What separates a delusion from, say, simply being misinformed? It's the inability to change your thinking, even when there is evidence against your belief, says Dr. Patel. Examples can include believing that a person is trying to poison your food or drinks, a spouse is having an affair, or family members are stealing from you.

What Are the Risk Factors for PDP?

“Patients with PD may develop a wide spectrum of non-motor symptoms during illness,” says Ann Kriebel-Gasparro, DrNP, a family and gerontological nurse practitioner in Ardmore, PA, and faculty member at Walden University. “Psychosis is a common non-motor symptom of PD.” Kriebel-Gasparro notes that Parkinson's disease psychosis is a leading cause of disability and nursing home placement for PD patients, and impacts quality of life for both patients and their caregivers. “PDP has a lifetime prevalence of up to 60% among PD patients," she says. "Risk factors include older age, greater disease severity, affective disorder, greater autonomic symptom burden, disorders of sleep and wakefulness, and cognitive impairment.”

How Do You Treat Hallucinations, Illusions, and Delusions?

Dealing with hallucinations, illusions, and delusions is frustrating and at times scary. While the trio of psychosis symptoms are different, the plan for treating them is the same: Your neurologist can help by adjusting your PD medications, which can sometimes lead to psychosis symptoms. A psychiatrist can help you manage your symptoms if attempts to control the psychosis through PD medication adjustments are unsuccessful. Counselors, support groups, and care givers also play important support roles. Nothing about Parkinson's is easy, and that includes psychosis. But there is every reason to believe you can manage your symptoms with the right approach.

Judy Koutsky
Meet Our Writer
Judy Koutsky

Judy Koutsky is an award-winning writer and editor and her work has appeared in over 30 publications including Conde Nast Traveler, Travel + Leisure, Parents, WebMD, Prevention and Scholastic. You can see her work at JudyKoutsky.com or follow her on Instagram @JudyKoutsky.