Relapse in Cardiac Sarcoidosis: Patterns and Predictors on Serial 18F-FDG PET Imaging.

BACKGROUND: Cardiac sarcoidosis follows a relapsing-remitting course, but imaging patterns and predictors of relapse remain poorly defined. OBJECTIVES: To characterize spatial and metabolic features of relapse in cardiac sarcoidosis and identify predictors using serial 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). METHODS: Patients with cardiac sarcoidosis who underwent three serial FDG-PET-baseline (PET 1), response (PET 2), and follow-up (PET 3)-at a tertiary center in Toronto, Canada (2011-2024) were included. Eligibility required abnormal myocardial FDG uptake at PET 1 and metabolic response at PET 2, defined as ≥20% reduction in total cardiac metabolic activity (tCMA) relative to PET 1. Left ventricular segmental FDG analysis assessed spatial patterns. Candidate predictors included baseline inflammatory burden and response-phase imaging features. Imaging-defined relapse was defined as ≥20% increase in tCMA from PET 2 to PET 3. Logistic regression identified predictors. RESULTS: Among 50 patients (median age 54; 60% male), 23 (46%) had relapse. Most relapses (91%) occurred in previously affected myocardial segments, with 70% showing lower FDG intensity and extent. Relapsed patients had higher baseline tCMA (564.0 vs 120.1; p=0.006) and more extracardiac involvement (2.61 vs 1.19 organs; p=0.01). Higher odds of relapse were observed among patients with residual myocardial FDG uptake (adjusted OR 5.30; 95% CI, 1.14-29.13; p=0.039). CONCLUSIONS: Relapse occurred in nearly half of patients after an initial response, typically involving previously affected myocardial regions with lower inflammatory burden. Residual FDG uptake on response-phase imaging was associated with relapse, supporting the role of serial FDG-PET for surveillance in cardiac sarcoidosis. (Word count: 250/250).