Whole body and cardiac metaiodobenzylguanidine kinetics in Parkinson disease and multiple system atrophy: implications for the diagnostic role of imaging.

Purpose of the Report: This study investigates whether combined analysis of I-123 metaiodobenzylguanidine (MIBG) kinetics in the heart and in the whole body can improve the accuracy of differential diagnosis between idiopathic Parkinson disease (PD) and a Parkinson variant of multiple system atrophy (MSA-P). Materials and Methods: A total of 30 patients with clinical suspicion of PD (n = 16) or MSA-P (n = 14) underwent MIBG whole-body planar imaging. Final diagnosis was confirmed at follow-up. Images were collected 30 minutes and 4 hours after tracer injection. Myocardial uptake was evaluated by measuring heart/mediastinum (H/M) ratio and the percent fraction of the injected dose retained by the heart (calculated by whole-body counts). Tracer washout was measured from both the heart and the whole body. RESULTS: H/M ratio was lower in PD than in MSA-P at early imaging (1.32 ± 0.21 vs. 1.81 ± 0.46, respectively, P < 0.01), although a large overlap in individual data was observed. By contrast, % of injected dose taken up by the heart documented a large difference between PD and MSA-P (0.97% ± 0.51% vs. 1.91% ± 0.66% of the dose, P < 0.01), and a very small overlap in individual values. There was no difference in the heart washout between the 2 Groups (31% ± 13% vs. 32% ± 15%, P = 0.9), while tracer loss from the whole body was higher in PD than in MSA-P (29% ± 12% vs. 19% ± 10%, P < 0.01). CONCLUSIONS: PD and its correlated global postganglionic dysfunction alter MIBG kinetics in the heart and in the whole body. Image analysis accounting for tracer kinetics in the whole body may improve the diagnostic accuracy of this test in patients with suspected PD or MSA-P.