Radioactive iodine labelled MIBG cardiac sympathetic imaging is less promising in differentiating PD from other parkinsonism for early onset patients

Objectives: MIBG cardiac sympathetic imaging has been demonstrated to be promising in differentiating Parkinson’s disease (PD) from other neurodegenerative parkinsonism. Age at onset has an impact on cardiac MIBG uptake in PD, but not in multiple system atrophy (MSA) or progressive supranuclear palsy (PSP). In the present study, we hypothesized that there is an interaction between age at onset and disease group for H/M ratios. Radioactive iodine labeled MIBG cardiac sympathetic imaging is less promising in differentiating PD from other parkinsonism for early-onset patients.

Methods: Ninety-two patients with parkinsonism, including 60 patients with PD and 32 patients with Parkinson “plus” syndrome (PPS), were retrospectively reviewed. Patients were grouped into the early-onset group (age at onset ≤50 y/o) and late-onset group (age at onset >50 y/o) according to the time they first developed motor symptoms. ¹³¹I-MIBG cardiac scintigraphy was done 15min post injection for early images and 4h for the delayed scan. Regions of interest (ROIs) were manually drawn over heart contour (H) and upper mediastinum (M) for each image. Average counts per pixel in the ROIs were used to calculate heart-to-mediastinum (H/M) ratio.

Results: The clinical data were summarized in Table 1. There was no significant difference in age, age at onset, or gender between PD and other parkinsonism. The disease duration of patients in the PD group was significantly longer than PPS patients. After controlling for disease duration using one-way ANCOVA, there was a statistically significant difference in the adjusted H/M ratio (P<0.001 for both early and delayed scan) between PD and PPS patients. Using two-way ANOVA, there was a statistically significant interaction between disease group and age at onset for both early (P=0.008) and delayed H/M ratio (P=0.043). Subgroup analysis (Table 2) demonstrated that no significant difference was found between PD and PPS patients in the early-onset group for either early (2.03±0.42 vs. 2.01±0.29, P=0.882) or delayed H/M ratio (2.05±0.56 vs. 2.22±0.52, P=0.468). In the late-onset group, patients with PD demonstrated significant lower H/M ratio compared with PPS patients for both early (1.71±0.32 vs. 2.14±0.34, P<0.001) and delayed images (1.58±0.42 vs. 2.25±0.57, P<0.001). Using ROC analysis, H/M ratio can be used to differentiate PD from PPS patients (AUC=0.749 and 0.784 for the early and delayed scan, respectively). By deselecting early-onset patients, the discrimination power can be further improved (AUC=0.812 and 0.824 for the early and delayed scan, respectively) in late-onset patients.

Conclusions: There is an interaction between age at onset and disease group for H/M ratios. ¹³¹I-MIBG cardiac sympathetic imaging is less promising in differentiating PD from other parkinsonism for early-onset patients.