Summary: People diagnosed with schizophrenia have an increased risk of developing Parkinson’s disease later in life, researchers report. The reason could be due to alterations in the brain’s dopamine system cause as a result of dopamine receptor antagonists or neurophysiological changes associated with schizophrenia itself.
Source: University of Turku
A new study conducted at the University of Turku, Finland, shows that patients with a schizophrenia spectrum disorder have an increased risk of Parkinson’s disease later in life. The increased risk may be due to alterations in the brain’s dopamine system caused by dopamine receptor antagonists or neurobiological effects of schizophrenia.
The record-based case-control study was carried out at the University of Turku in collaboration with the University of Eastern Finland. The study examined the occurrences of previously diagnosed psychotic disorders and schizophrenia in over 25,000 Finnish Parkinson’s disease (PD) patients treated in 1996-2019.
In the study, patients with Parkinson’s disease were noted to have previously diagnosed psychotic disorders and schizophrenia more often than the control patients of the same age not diagnosed with PD.
“Previous studies have recognised several risk factors for PD, including age, male sex, exposure to insecticides, and head injuries. However, the current understanding is that the development of PD is due to a joint effect of different environment, hereditary, and patient-specific factors. According to our results, a previously diagnosed psychotic disorder or schizophrenia may be one factor that increases the risk of PD later in life,” says Doctoral Candidate Tomi Kuusimäki from the University of Turku who was the main author of the research article.
Study changes conception of the association between Parkinson’s disease and schizophrenia
PD is currently the most rapidly increasing neurological disorder in the world. It is a neurodegenerative disorder that is most common in patients over 60 years of age. The cardinal motor symptoms include shaking, stiffness and slowness of movement. In Finland, circa 15,000 patients are currently living with a PD diagnosis.
In Parkinson’s disease, the neurons located in the substantia nigra in the midbrain slowly degenerate, which leads to deficiency in a neurotransmitter called dopamine. As for schizophrenia, the dopamine level increases in some parts of the brain.
In addition, the pharmacotherapies used in the primary treatment of PD and schizophrenia appear to have contrasting mechanisms of action. PD symptoms can be alleviated with dopamine receptor agonists, whereas schizophrenia is commonly treated with dopamine receptor antagonists.
“The occurrence of Parkinson’s disease and schizophrenia in the same person has been considered rare because these diseases are associated with opposite alterations in the brain’s dopamine system. Our study changes this prevailing conception,” says Kuusimäki.
About this schizophrenia and Parkinson’s disease research news
Source: University of Turku
Contact: Tomi Kuusimäki – University of Turku
Image: The image is in the public domain
Original Research: Open access.
“Increased Risk of Parkinson’s Disease in Patients With Schizophrenia Spectrum Disorders” by Tomi Kuusimäki et al. Movement Disorders
Increased Risk of Parkinson’s Disease in Patients With Schizophrenia Spectrum Disorders
PD comorbid with schizophrenia has been considered rare because these diseases associate with opposite alterations in the brain dopamine system. The objective of this study was to investigate the risk of PD after a diagnosis of a schizophrenia spectrum disorder.
Regionally, this was a retrospective record‐based case–control study. The cohort included 3045 PD patients treated 2004–2019 in southwestern Finland. Nationally this was a nested case–control study using registers to examine Finnish patients who received a clinically confirmed PD diagnosis 1996–2015 (n = 22,189). PD patients with previously diagnosed schizophrenia spectrum disorder (separate analysis for schizophrenia) were included. Comparable non‐PD control groups were derived from both data sets. All PD diagnoses were based on individual clinical examinations by certified neurologists.
In PD patients, the prevalence of earlier schizophrenia spectrum disorder was 0.76% in regional data and 1.50% in nationwide data. In age‐matched controls, the prevalence in the regional and national data was 0.16% and 1.31%, respectively. The odds ratio for PD after schizophrenia spectrum disorder diagnosis was 4.63 (95% CI, 1.76–12.19; P < 0.01) in the regional data and 1.17 (95% CI, 1.04–1.31; P < 0.01) in the national data.
Schizophrenia spectrum disorder increases the risk of PD later in life. This association was observed in both individual patient data and nationwide register data. Therefore, despite the opposite dopaminergic disease mechanisms, schizophrenia spectrum disorder increases rather than decreases the risk of PD. The increased PD risk could be related to risk‐altering effects of dopamine receptor antagonists or to the increased vulnerability of the dopamine system induced by illness phase‐dependent dopamine dysregulation in schizophrenia/schizophrenia spectrum disorder.