Combination of midbrain-to-pontine ratio and cardiac MIBG scintigraphy to differentiate Parkinson's disease from multiple system atrophy and progressive supranuclear palsy

BACKGROUND: An early clinical differentiation between Parkinson's disease (PD) and multiple system atrophy (MSA) or progressive supranuclear palsy (PSP) remains a challenge. The purpose of this study was to evaluate the usefulness of the combination use of midbrain-to-pontine ratio (M/P ratio) from magnetic resonance imaging (MRI) with cardiac (123)I-metaiodobenzylguanidine (MIBG) uptake for differentiating PD from MSA and PSP. METHODS: Ninety-six parkinsonian patients (70 PD, aged 68.5 ± 9.5 years; 16 MSA, aged 67.9 ± 7.5 years; 10 PSP, aged 70.4 ± 9.4 years) who underwent MRI and cardiac MIBG scintigraphy were included in this study. Receiver operating characteristic (ROC) curve analysis was used to assess the sensitivity and specificity for distinguishing PD from MSA and PSP patients. The diagnostic accuracy of these tests was also assessed among patients at the early disease stage (defined as patients with a disease duration of 3 years or less). RESULTS: The individual diagnostic sensitivity of the M/P ratio and cardiac MIBG scintigraphy was 87.1% and 67.1% in PD vs. MSA and 78.6% and 67.1% in PD vs. PSP, respectively. The diagnostic specificity of the M/P ratio and cardiac MIBG scintigraphy was 56.3% and 100% in PD vs. MSA and 70.0% and 90% in PD vs. PSP, respectively. With the optimal cutoff values, at least one positive result (either the M/P ratio or cardiac MIBG revealed abnormalities) improved sensitivity (95.7%) without decrease of specificity (56.3%) in PD vs. MSA, as well as in PD vs. PSP (100% sensitivity, 70.0% specificity). In contrast, both positive results of two tests had good specificity but low sensitivity in PD vs. MSA (60.0% sensitivity and 100% specificity) and in PD vs. PSP (47.1% sensitivity and 90% specificity). Similar trends were observed in early-stage patients. CONCLUSION: Although M/P ratio alone was potentially useful for distinguishing PD from MSA or PSP, the combined use with cardiac MIBG scintigraphy can further improve the diagnostic accuracy of PD from MSA or PSP.