Background Although most patients with Parkinson's disease (PD) show decreased cardiac 123I-metaiodobenzylguanidine (MIBG) uptake, some exhibit normal uptake. We evaluated the clinical characteristics of such patients. Methods We enrolled 154 non-demented patients showing parkinsonism with normal cardiac MIBG uptake and had been clinically followed up during 29.9 ± 27.6 months. We defined the patients who did not fit the exclusion criteria for PD and demonstrated > 30% reduction in the Unified Parkinson's Disease Rating Scale (UPDRS) motor score after anti-Parkinson agent administration as probable PD. We compared clinical characteristics and the cardiac MIBG heart-to-mediastinum (H/M) ratio between the probable PD group (N = 37) and other groups (N = 117). Results The probable PD group showed significantly higher UPDRS motor scores and greater incidence of tremor/rigidity than those of other groups. In addition, they showed a significantly lower cardiac MIBG H/M ratio in the delayed phase (delayed, p < 0.0001). Washout-rate (WR) was significantly higher in probable PD cases (p < 0.0001). Among 16 probable PD patients undergoing serial cardiac MIBG scintigraphy, the delayed phase cardiac MIBG H/M ratio showed a significant decrease and WR significantly increased during follow-up periods. Conclusions An increase in WR and lower delayed phase cardiac MIBG uptake were found to be characteristics of such patients.
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