Patients with a schizophrenia spectrum disorder have an increased risk of Parkinson's disease later in life.
The study indicates that the increased risk may be due to alterations in the brain's dopamine system caused by dopamine receptor antagonists or neurobiological effects of schizophrenia.
"According to our results, a previously diagnosed psychotic disorder or schizophrenia may be one factor that increases the risk of Parkinson's disease later in life," said researcher Tomi Kuusimäki from the University of Turku in Finland.
For the study, published in the journal Movement Disorders, the researchers examined the occurrences of previously diagnosed psychotic disorders and schizophrenia in over 25,000 Finnish Parkinson's disease patients treated between 1996 and 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 Parkinson's disease.
Parkinson's disease 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 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 Parkinson's disease and schizophrenia appear to have contrasting mechanisms of action.
Parkinson's disease symptoms can be alleviated with dopamine receptor agonists, whereas schizophrenia is commonly treated with dopamine receptor antagonists.