Semi-quantitative metabolic values on FDG PET/CT including extracardiac sites of disease as a predictor of treatment course in patients with cardiac sarcoidosis

BACKGROUND Cardiac sarcoidosis is associated with major adverse cardiac events including cardiac arrest, for which anti-inflammatory treatment is indicated. Oral corticosteroid is the mainstay among treatment options; however, adverse effects are a major concern with long-term use. It would be beneficial for providers to predict treatment response and prognosis for proper management strategy of sarcoidosis, though it remains challenging. Fluorine (F)-18 fluorodeoxyglucose (FDG)-positron emission tomography(PET)/computed tomography(CT) has an advantage over anatomical imaging in providing semi-quantitative functional parameters such as standard uptake value (SUV), metabolic volume, and total lesion glycolysis (TLG), which are well-established biomarkers in oncology. However, the relationship between these parameters and treatment response has not been fully investigated in cardiac sarcoidosis. Also, the prognostic value of extracardiac active inflammation noted on FDG-PET/CT in the setting of cardiac sarcoidosis is unclear. The aim of this retrospective study was to investigate the prognostic value of semi-quantitative values of both cardiac and extracardiac disease sites derived from FDG-PET/CT in predicting treatment course in cardiac sarcoidosis. METHODS Sixteen consecutive patients with suspected cardiac sarcoidosis, who demonstrated abnormal myocardial activity on cardiac-inflammation FDG-PET/CT encompassing the entire chest/upper abdomen and subsequently underwent corticosteroid therapy for diagnosis of active cardiac sarcoidosis, were included. Semi-quantitative values of hypermetabolic lesions were derived from all visualized organ system and were compared to daily corticosteroid dose at 6 months. RESULTS  Of the 16 patients, 81.3% (13/16) of the patients showed extracardiac involvement. The lesion with the greatest SUV was identified in the heart in 11 patients (68.7%), in the liver in 1 patient (6.3%), and in lymph nodes in 4 patients (25%). The maximum SUV across all visualized organ systems including the heart were 8.8 ± 3.1 for the patients with corticosteroid dose ≤ 10 mg and 12.5 ± 3.3 for those with > 10 mg (P = 0.04). Metabolic volume and TLG across all visualized organ systems or any values in the heart alone showed no significant statistical difference between the two groups. CONCLUSIONS Maximum SUV across all involved organ-systems of the chest and upper abdomen, not that of the heart alone, could be a predictor of treatment course of steroid therapy at 6 months in patients with active cardiac sarcoidosis.