[123I]-Meta-Iodobenzylguanidine Scintigraphy in Sarcoidosis: Exploring Cardiac Autonomic Dysfunction in Patients with Unexplained Cardiac Symptoms

Background/Objectives: Sarcoidosis is a systemic inflammatory disease that can cause cardiac autonomic dysfunction (SCAD), often underrecognized despite its clinical importance. While [ ¹⁸F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography ([ ¹⁸F]FDG PET/CT) and cardiac magnetic resonance imaging (CMR) assess cardiac involvement, [ ¹²³I]-meta-iodinebenzylguanidine ([ ¹²³I]MIBG) scintigraphy evaluates cardiac sympathetic innervation, offering complementary insights to potentially improve SCAD detection and management. This retrospective study explores the role of [ ¹²³I] MIBG scintigraphy in detecting SCAD among patients with unexplained cardiac symptoms. It focuses on its potential to provide complementary diagnostic information in patients where established imaging techniques, such as [ ¹⁸F]FDG PET/CT and CMR, fail to detect cardiac sarcoidosis. Methods: Sarcoidosis patients referred to the St. Antonius Hospital (2017–2024) who underwent [ ¹²³I]MIBG scintigraphy were included. Collected data encompassed demographics, SCAD symptoms, cardiac imaging findings, and carvedilol treatment outcomes. [ ¹²³I] MIBG abnormalities were defined as a heart-to-mediastinal ratio ≤1.6 or a washout rate ≥20%. Results: Among the final cohort of 40 sarcoidosis patients with unexplained cardiac symptoms and normal [ ¹⁸F]FDG PET/CT and CMR findings, 19 patients (48%) showed abnormal [ ¹²³I] MIBG scintigraphy results suggestive of SCAD. No significant differences were observed in clinical characteristics between patients with normal and abnormal [ ¹²³I]MIBG findings. Of the 16 patients treated with carvedilol, 88% reported symptom improvement, although 50% experienced side effects. Conclusions: [ ¹²³I]MIBG scintigraphy revealed abnormalities in a substantial number of sarcoidosis patients with unexplained cardiac symptoms despite normal [ ¹⁸F]FDG PET/CT and CMR. These findings indicate a potential role for [ ¹²³I]MIBG in detecting SCAD, but prospective studies are needed to confirm their clinical significance.