Usefulness of the combination of iodine-123-metaiodobenzylguanidine scintigraphy and iodine-123-ioflupane scintigraphy in new-onset Parkinson’s disease

OBJECTIVES: The aim of this study was to study the significance of combining iodine-123-cardiac metaiodobenzylguanidine scintigraphy (I-MIBG scintigraphy) and iodine-123-ioflupane (I-ioflupane) dopamine transporter scintigraphy (I-ioflupane scintigraphy) in patients suspected of having Parkinson's disease (PD). PATIENTS AND METHODS: We carried out a retrospective study from April 2014 to December 2015 in 48 patients suspected of having new-onset PD who underwent both I-MIBG and I-ioflupane scintigraphies within 3 months. Cases included 37 patients diagnosed as having PD. Controls included 11 patients who had never been diagnosed as having PD or other diseases showing parkinsonism. The cutoff for diagnosing PD was a heart to mediastinum ratio (H/M ratio) of less than or equal to 2.2 for I-MIBG scintigraphy in the delayed phase and a specific binding ratio (SBR) of less than or equal to 3.8 for I-ioflupane scintigraphy. The combined use of both scintigraphies was studied using the formula SBR×H/M ratio as a marker for the logistic regression model. RESULTS: Sixteen (33.3%) patients had SBR of greater than 3.8: eight with PD; eight were controls. Five of eight patients had an H/M ratio of less than or equal to 2.2 (62.5%) and had PD. In the receiver-operating characteristic analysis, the SBR×H/M ratio cutoff was 12.5, with an area under the curve of 0.844 (95% confidence interval: 0.619-1). In an age-adjusted regression analysis in patients with SBR of greater than 3.8, the SBR×H/M ratio was associated significantly with an odds ratio of 0.69 (95% confidence interval: 0.48-0.98, P=0.041). CONCLUSION: If SBR is greater than 3.8, the SBR×H/M ratio can help diagnose PD. The combined use of the two scintigraphies can improve the diagnosis of PD.