Neuropsychiatric symptoms and striatal monoamine availability in early Parkinson’s disease without dementia

Background and objective: Neuropsychiatric symptoms are relatively common in Parkinson’s disease (PD). Many studies have revealed that striatal monoamine availability is associated with specific neuropsychiatric symptoms. This study was aimed to investigate the association between comprehensive neuropsychiatric symptoms and striatal monoamine availability in patients with early PD without dementia. Methods: A total of 156 newly diagnosed patients with PD without dementia were included. All patients’ mental and behavioral problems were assessed with the 12-item Neuropsychiatric Inventory (NPI). They underwent positron emission tomography (PET) with ¹⁸F-N-(3-fluoropropyl)-2beta-carbon ethoxy-3beta-(4-iodophenyl) nortropane and brain magnetic resonance imaging (MRI). Patients were divided into no neuropsychiatric symptoms and neuropsychiatric symptoms groups according to total NPI score. After normalizing the PET images to spatially normalized MRI, regional standardized uptake value ratios (SUVRs) with a volume of interest template were analyzed for the two groups. Results: Ninety-eight patients had more than one neuropsychiatric symptom. The SUVR of the thalamus in neuropsychiatric symptoms group was significantly lower than the SUVR in no neuropsychiatric symptoms group independent of age, sex, disease duration, or severity of motor symptoms. Conclusion: Patients with early PD who have neuropsychiatric symptoms had a lower monoamine availability in the thalamus than those with no neuropsychiatric symptoms. This finding suggests that decreased monoamine transporter availability in the thalamus may be an imaging biomarker of neuropsychiatric symptoms in patients with PD.