Background: Early diagnosis of Parkinson's disease (PD) is of primary importance. The
delayed (3-4 h after injection) Iodine-123-Metaiodobenzylguanidine (123I-mIBG) scintigraphy has
been proven to be effective in early differential diagnosis for Lewy body disease. But early imaging
(15-30 min after injection) has only been marginally studied for its possible diagnostic role. In
this prospective study, a threshold for the early Heart-to-Mediastinum (H/M) count ratio has been
investigated, obtaining a diagnostic accuracy analogous to conventional, delayed imaging.
Methods: One hundred and eight patients with suspected Parkinson's disease (PD) were acquired
after 15 and 240 minutes from the injection of 150-185 MBq of 123I-mIBG. The early and late
H/M (He/Me and Hl/Ml) were evaluated by drawing Region-of-Interests on the heart and the upper
half of the mediastinum. Optimal threshold (Youden index) and overall predictive performance
were determined by receiver operating characteristic curve, classifying tentatively patients having
an Hl/Ml lower than 1.6 as suffering from PD.
Results: He/Me was not significantly different from Hl/Ml (p-value=0.835). The Area-under-curve
was 0.935 (95%CI: 0.845-1.000). The He/Me optimal threshold was 1.66, with sensitivity, specificity,
and diagnostic accuracy of 95.5%, 85.7 and 90.7% respectively.
Conclusion: The He/Me Ratio is almost as accurate as the widely used delayed 123I-mIBG imaging,
reducing the burden of delayed imaging but preserving the diagnostic accuracy of the method.
Moreover the differential diagnosis in Parkinson's disease can be made in just 25 minutes against
the 4 hours currently needed, lowering costs of the healthcare system and improving patients compliance.