Diagnostic Efficacy of 123Iodo-Metaiodobenzylguanidine SPECT/CT in Cardiac vs. Neurological Diseases: A Comparative Study of Arrhythmogenic Right Ventricular Cardiomyopathy and α-Synucleinopathies

<b>Background/Objectives</b>: ¹²³Iodo-metaiodobenzylguanidine single photon emission computed tomography/computed tomography (¹²³I-MIBG SPECT/CT) is used to evaluate the cardiac sympathetic nervous system in cardiac diseases such as arrhythmogenic right ventricular cardiomyopathy (ARVC) and α-synucleinopathies such as Parkinson's diseases. A common feature of these diseases is denervation. We aimed to compare quantitative and semi-quantitative cardiac sympathetic innervation using ¹²³I-MIBG imaging of ARVC and α-synucleinopathies. <b>Methods</b>: Cardiac innervation was assessed using ¹²³I-MIBG SPECT/CT in 20 patients diagnosed with definite ARVC and 8 patients with clinically diagnosed α-synucleinopathies. Heart-to-mediastinum-ratio (H/M-ratio), as semi-quantitative, was evaluated. Additionally, standardized uptake value (SUV), as quantitative, was measured as SUV_median, SUV_max, and SUV_peak in the left ventricle (LV), the right ventricle (RV), and in the global heart, based on a CT scan following quantitative image reconstruction. <b>Results</b>: The quantification of ¹²³I-MIBG uptake in the LV, the RV, and the global heart was feasible in patients suffering from α-synucleinopathies. SUV_median, and SUV_peak demonstrated a significant difference between ARVC and α-synucleinopathies across all regions, with the α-synucleinopathy group showing a lower uptake. In addition, the H/M ratio showed significantly lower uptake in patients with α-synucleinopathies than in patients with ARVC. <b>Conclusions</b>: Patients with α-synucleinopathies demonstrate significantly lower cardiac innervation in semi-quantitative and quantitative examinations than ARVC patients. The comparison of semi-quantitative and quantitative examinations suggests that quantitative examination offers an advantage. Quantitative analysis can be performed separately for the LV, RV, and global heart. However, analyzing the LV or RV does not provide additional benefit over analyzing the global heart in distinguishing between α-synucleinopathies and ARVC. Considering the different clinical manifestations of these two diseases, the absolute SUV values should not be generalized across different pathologies, and disease-specific ranges should be used instead.