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High frequency of psychosis in late-stage Parkinson's disease

Original author: Chendo I, Fabbri M, Godinho C, et al. (2021) (DOI: 10.1016/j.prdoa.2021.100119)



Content writer – Clinical

November 09, 2022


Parkinson’s disease (PD) is a neurological disorder observed mostly in elderly individuals. The symptoms include tremors, muscle stiffness, slow motion, and loss of balance. It is caused when neurons of the basal ganglia region of the brain fail to produce the neurotransmitter dopamine which regulates movement.

Psychosis is a frequent non-motor symptom (NMS) in Parkinson’s disease (PD). Its presence increases with disease progression and is associated with poor prognosis such as greater motor disability, affective dysfunction, nursing home placement, dementia, and mortality. The pattern of psychotic symptoms in Parkinson’s disease (PDP) differs from the psychosis in other neurodegenerative disorders such as schizophrenia. They include hallucinations mainly visual and delusions, and other minor symptoms. The reason for this may be attributed to the different neurobiology of psychosis in PD although the basic mechanism of psychosis is the same for all.

Estimates of the prevalence of PDP vary widely due to the usage of different samples and different diagnostic criteria to define psychosis. But it is very well established that psychosis progression increases with increasing age in Parkinson’s disease. The National Institute of Neurological Disorders and Stroke (NINDS)/ National Institute of mental health (NIMH) working group proposed the set of standard diagnostic criteria for psychosis in PD in 2007.

This criterion has not been used to determine the presence of psychosis in PD until now. So this study aims to evaluate the presence of psychosis in PD using these criteria with the help of a clinical diagnostic interview.


In a cross-sectional study, a clinical observation was performed to evaluate the presence of psychiatric disturbances (psychotic disorders, mood disorders, anxiety disorders, impulsive-compulsive disorders, and others) and characterize the neuropsychiatric symptoms occurring in a hospital-based sample of LSPD patients.

Recruitment of patients:

The inclusion criteria :

  • PD according to the UK Brain Bank criteria

  • LSPD (patients with symptoms onset from a minimum of 7 years.


 Exclusion criteria:

  • If dementia is present before Parkinson’s onset or dementia within a year following PD diagnosis.

  • If they had delirium at the moment of clinical evaluation.

Assessment procedures and data collection:

Patients were subjected to psychiatric, neurological, and neuropsychological evaluations performed by a psychiatrist, a movement disorders expert, and a neuropsychologist.

A psychiatric assessment was conducted by a trained psychiatrist who performed a Clinical Diagnostic Interview (CDI). The CDI was considered the gold standard method for PDP diagnosis, in agreement with the NINDS/NIMH diagnostic criteria. Details of medical and PD history, drug therapy, and demographic variables were obtained by direct interview with the patient and a reliable informant (family caregivers or formal caregivers from nursing homes) as well as through a review of the patient’s clinical neurologic records. Around 95% of all evaluations took place in a single session and were conducted either in patientś homes or in nursing homes. Patients were classified as psychosis positive according to the NINDS/ NIMH diagnostic criteria which include:

  1. The presence of at least one of the following characteristic symptoms – illusions, false sense of presence, hallucinations, delusions;

  2. A diagnosis of PD made according to UK Brain Bank criteria and made before the onset of psychotic symptoms;

  3. The psychotic symptoms were  recurrent or continuous for at least one month; and

  4. Exclusion of other causes such as dementia with Lewy bodies, schizophrenia, schizoaffective disorder, delusional disorder, mood disorder with psychotic features, and delirium

Neurological assessment was performed using the Movement Disorders Society – Unified Parkinson Disease Rating Scale (MDS-UPDRS).

Neuropsychiatric functions were also assessed by the same neurologist and included behavioral symptoms using the NPI. Dementia was diagnosed according to the MDS PDD Level II criteria based on neuropsychological and functional autonomy assessment and mild cognitive impairment (MCI) was diagnosed using the MDS Level II criteria.


In conclusion, psychotic symptoms were reported in around 55% of LSPD patients and among them, around 75% of patients had at least one co-morbid psychiatric diagnosis.

The use of a Clinical Diagnostic interview (CDI) along with this measuring scale helps to increase the sensitivity of detection of diseases in cognitive impairment patients.

Impact of research

  • It applied a new methodology in the context of PD.

  • Evidence for allied health professionals and physicians to know the prevalence of psychosis in Parkinson’s disease.

  • Helps to differentiate PDP from other psychosis.

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