Striatal dopamine activity and myocardial ¹²³I-metaiodobenzylguanidine uptake in early Parkinson's disease

Introduction: Dopamine transporter imaging and myocardial ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) scintigraphy have been widely used to diagnose and discriminate degenerative parkinsonism. Many studies have reported that both imaging findings are associated with a variety of motor and non-motor phenomena in Parkinson's disease (PD). However, the association between striatal dopamine activity and myocardial ¹²³I-MIBG uptake has not been well investigated. The objective of this study is to identify the dopamine transporter activity of the corpus striatum and thalamus according to myocardial ¹²³I-MIBG uptake in PD. Methods: Ninety-six newly diagnosed, non-medicated PD patients were enrolled. All patients underwent ¹²³I-MIBG myocardial scintigraphy, positron emission tomography (PET) using ¹⁸F[sbnd]N-(3-fluoropropyl)-2beta-carbon ethoxy-3beta-(4-iodophenyl) nortropane and T1-weighted magnetic resonance imaging (MRI). Patients were stratified into normal and decreased ¹²³I-MIBG groups according to their delayed heart-to-mediastinum ratio (cutoff value = 1.78). After normalizing the PET images with spatially normalized MRI, the regional standardized uptake value ratios (SUVRs) were analyzed with a volume-of-interest template between the two groups. Results: Thirty-one patients showed normal myocardial ¹²³I-MIBG uptake, and 65 patients showed reduced uptake. The SUVR of the globus pallidus in the group with reduced ¹²³I-MIBG uptake was significantly lower than the SUVR in the normal ¹²³I-MIBG uptake group. The heart-to-mediastinum ratio was correlated well with the SUVR of the globus pallidus, independent of age, disease duration, and the severity of motor symptoms. Conclusion: Early PD patients with normal ¹²³I-MIBG uptake showed a relatively preserved dopamine reserve in the globus pallidus than patients with reduced ¹²³I-MIBG uptake.