Clinical and prognostic significance of abnormal 18F-FDG PET findings in patients with cardiomyopathy

Background 18F-labeled Fluorodeoxyglucose positron emission tomography (FDG-PET) has emerged as a valuable imaging modality for evaluating myocardial metabolism, particularly in inflammatory and infiltrative cardiomyopathies. However, its role in the differential diagnosis of various cardiomyopathy subtypes, as well as prognostic significance of abnormal FDG uptake in the myocardium, remains unclear. Therefore, we investigated the final diagnoses of patients who had abnormal cardiac FDG uptake and compared their prognoses based on their respective underlying cardiomyopathy subtypes. Methods We retrospectively analyzed 1,029 FDG-PET examinations performed for cardiomyopathy evaluation at our institution between 2019 and 2024. Cases with multiple examinations or those with a pre-established diagnosis were excluded. We investigated the final diagnoses of patients who showed abnormal FDG uptake, and analyzed their subsequent prognoses. Results During the study period, 495 patients who underwent FDG-PET for primary cardiac evaluation were included in the final analysis. Among them, 209 (42%) were diagnosed as having abnormal FDG-uptake. While the most common diagnosis was cardiac sarcoidosis (CS) (n=95, 45%), more than half of the patients did not meet the definitive diagnostic criteria for CS (non-CS, n=1１4, 55%). Figure 1 illustrates the distribution of the final diagnoses among the study patients. There were no significant differences between CS and non-CS patients regarding gender (male: 60% vs 53%), LVEF (41±１２ vs 44±14%) and BNP levels (221[5.8-1496] vs 299 [4-7228] pg/ml), except for age (CS vs non-CS, 65±13 vs 60±15 years, p=0.028). Corticosteroid therapy was administered to 72% of patients with CS, compared to only 9% in non-CS patients. During the mean follow-up of 3.6 years, the mortality rate was comparable between the groups (CS vs non-CS, 10.7% vs 13.5%, p=0.88, Figure 2). Conclusions Although FDG-PET may be a valuable tool for evaluating cardiomyopathy, abnormal FDG-uptake was not an uncommon finding even in patients without CS. Clinical manifestation and cardiac function, and mortality were comparable between CS and non-CS patients, despite differences in corticosteroid use.