Often under-recognized and under-diagnosed in people with Parkinson’s disease are a range of non-motor symptoms which can accompany the hallmark motor disturbances of this progressive, neurodegenerative brain disease. Among these are psychotic symptoms which can present as hallucinations and/or delusions. Roughly 40% of people with Parkinson’s disease will develop such symptoms, leading to poor quality of life and costly nursing home care for individuals and their caretakers.¹˒²
This primer collection includes more details and management field tips.
Parkinson’s Disease Psychosis Definition and DSM-5 Criteria
Various descriptions are used to define psychosis related to Parkinson’s disease, all of which fundamentally characterize it as part of the non-motor symptoms of the disease.
DSM-5 Criteria
The DSM-5 places PDP under the category “Psychotic Disorder Due to Another Medical Condition” and include the following diagnostic criteria:³
prominent hallucinations or delusions that cannot be attributed to another mental disorder
episodes that cause significant impairment to the patient and cannot solely occur when the patient is delirious
psychosis that can be linked to the disease through laboratory findings, patient history, or on physical examination
Other Definitions
The American Parkinson’s Disease Association defines Parkinson’s disease psychosis (PDP) x as “a non-motor symptom of Parkinson’s disease that causes patients to experience hallucinations and/or delusions.”⁴
In 2007, the National Institute of Neurological Disorders and Stroke, National Institute of Mental Health (NINDS, NIMH) Work Group developed a shortened set of criteria for PDP. It requires a formal diagnosis of Parkinson’s and the exclusion of other more probable causes of psychosis. Characteristic symptoms of PDP, whether they be illusions, sense of presence, hallucinations, or delusions, must also be present for at least 1 month.⁵
Other experts prefer to apply a definition of psychosis associated with Parkinson’s disease only to those individuals who experience psychotic symptoms without insight into their symptoms.⁶
All of this suggests that a definition for PDP is still evolving, which makes screening difficult.
Parkinson’s Disease Psychosis Causes and Risks
While the cause of psychosis related to Parkinson’s was long thought to be a side effect of treatments used to address the motor symptoms of the disease, more recent understanding points to underlying mechanisms secondary to the disease itself, such as neuronal damage to multiple transmitter systems (dopamine, serotonin, and glutamate) caused by the deposition of Lewy bodies.¹˒²
People at risk of developing psychosis include:
those with more advanced Parkinson’s disease
those with cognitive impairment
advanced age
history of depression
sleep disorders
low daily activities
Psychotic Symptoms in Parkinson’s Disease
As with many conditions, prevalence rates for Parkinson’s disease-related psychosis can be difficult to determine with wide ranges given by different cohort studies. One of the most recent review articles (2020) places prevalence at about 40%.⁷
Presentation of psychosis also differs from person to person. Hallucinations and delusions are the main symptoms of psychosis related to Parkinson’s disease and can manifest in various ways with varying degrees of severity and disruption to a person’s life.⁸⁻¹¹
Hallucinations in Parkinson’s Disease
Visual hallucinations are most common, including seeing animals and people. Most studies suggest that hallucinations worsen over time, while other data show that in some patients, symptoms may remain stable over time and, in a minority of patients, may resolve.¹⁰
Up to 25% of people experience visual hallucinations while 20% show signs of auditory hallucinations. Complex visual hallucinations often involve persons, living or deceased, who are either known or unknown to the patient. They frequently present in dim lighting, last several seconds, and can occur multiple times a week. Individuals with PDP largely experience complex visual hallucinations over simple hallucinations such as flashes of light. Auditory hallucinations can involve hearing conversations or music in the background. Minor phenomena such as seeing inanimate objects as living, passage illusions (seeing animals or people passing by), or sense of presence (perceiving someone nearby), can exist in just over 70% of patients.⁹˒¹¹⁻¹⁴
PDP often begins with visual illusions and worsens to include visual hallucinations with insight, visual hallucinations without insight, and ultimately delusions.
Delusions in Parkinson’s Disease
Delusions are firm, false beliefs that are not based in reality. Delusions are less common than hallucinations and affect about 8% of people with Parkinson’s disease. Common delusions include:¹¹
paranoid or accusatory delusions, such as “my food is being poisoned”
delusions of jealousy (eg, unfaithful spouse)
somatic delusions (eg, obsessional preoccupation with body parts or health)
Onset of Psychotic Symptoms
Some data suggest that psychotic symptoms arise 10 years or more after the initial diagnosis of Parkinson’s disease, with more updated evidence suggesting that these symptoms can arise in nearly 50% of patients within 4 years of diagnosis.⁷
Data from hospital-based studies report hallucinations in 8% to 40% of patients receiving long-term treatment for Parkinson’s disease, while other recent data show that 55.4% of people with late-stage Parkinson’s disease (ie, 7 or more years after symptom onset of disease) have psychotic symptoms and 72.5% present with a comorbid psychiatric diagnosis.⁸
Treating Motor and Non-Motor Symptoms of Parkinson’s
Even with a better understanding of the etiology of and risk factors for Parkinson’s disease psychosis, diagnosis and treatment remain challenging. Making the differential diagnosis requires ruling out other conditions with similar symptoms including delirium with psychotic features, depression with psychosis, medication and substance-induced psychosis among others. Treatment requires carefully balancing management of the psychosis without exacerbating the underlying motor symptoms of Parkinson's disease.
Consequently, initial treatment should always be with non-pharmacologic interventions. If these are not helpful and the psychotic symptoms are impacting the quality of life of the patient and/or caregivers, pharmacotherapy is advised.
Use of atypical antipsychotics for treating PDP is controversial since these medications are not approved for this indication and carry significant risk of side effects. At present, only pimavanserin is FDA-approved for the treatment of PDP. However, it also carries a boxed warning relative to the potential for increased risk of death in people with dementia.¹⁵˒¹⁶