Abstract

Objective: Age at onset has an impact on cardiac meta-iodobenzylguanidine (MIBG) uptake in Parkinson’s disease (PD), but not in other parkinsonism. In the present study, we hypothesized that there is an interaction between age at onset and disease group for heart-to-mediastinum (H/M) ratios.

Methods: Ninety-two patients with parkinsonism, including 60 patients with PD and 32 patients with other neurodegenerative parkinsonism, 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 and heart-to-mediastinum ratio was used to quantify cardiac uptake.

Results: 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 demonstrated that no significant difference was found between PD and other neurodegenerative parkinsonism 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 patients with PD, there was significant difference in H/M ratio for both early (P=0.004) and delayed scan (P=0.002) between early-onset and lateonset patients. In patients with other neurodegenerative parkinsonism, no significant difference was found in H/M ratio for either early (P=0.314) or delayed scan (P=0.902) between early-onset and late-onset patients. Using ROC analysis, H/M ratio can be used to differentiate PD from other neurodegenerative parkinsonism (AUC=0.749 and 0.784 for early and delayed scan, respectively). By deselecting early-onset patients, the discrimination power can be further improved (AUC=0.812 and 0.824 for early and delayed scan, respectively) in late-onset patients.

Conclusion: 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.

Keywords: 131I-MIBG, cardiac sympathetic scintigraphy; Parkinson’s disease; parkinsonism; age at onset; early onset parkinsonism; progressive supranuclear palsy; multiple system atrophy; interaction effect.