Suppression of Myocardial 18F-FDG Uptake Through Prolonged High-Fat, High-Protein, and Very-Low-Carbohydrate Diet Before FDG-PET/CT for Evaluation of Patients With Suspected Cardiac Sarcoidosis

Background: A major obstacle in using FDG-PET/CT to diagnose cardiac sarcoidosis (CS) is the unpredictable physiological myocardial FDG uptake. We hypothesized that a prolonged 72-hour pretest high-fat, high-protein, and very-low-carbohydrate (HFHPVLC) diet preparation could suppress physiologic myocardial uptake of FDG and thus help to identify active CS. Methods: This retrospective study included 215 FDG-PET/CT tests from 207 patients with biopsy-proven sarcoidosis and clinical suspicion for CS between July 2014 and December 2015. The patients were classified into 2 groups. Group 1 included 12 FDG-PET/CT scans from 12 patients who had 24-hour or less pretest HFHPVLC diet preparation. Group 2 included 203 FDG-PET/CT scans with 72-hour HFHPVLC diet before FDG-PET/CT. Nonadherent patients and patients with cancer were excluded. Cardiac FDG uptake was classified as: "none" and "ringlike diffuse at base" (negative for CS), "focal" (positive for CS), and "diffuse" (indeterminate for CS). FDG uptake in myocardial lesions was measured as SUVmax and compared with SUVmean of mediastinal blood pool. Final diagnoses were made with consensus among physicians in view of all available clinical information including cardiac MRI and echocardiogram results. Results: In group 1, there were 1 (1/12, 8.3%) positive, 5 (5/12, 41.7%) indeterminate, and 6 (6/12, 50.0%) negative for CS. In group 2, 10 patients were excluded (6 patients because of noncompliance with diet, 2 patients with concurrent diagnosis of cancers, 2 patients because of insulin and steroid use within 4 hours before PET/CT); the remaining 185 patients had 193 FDG PET/CT tests (8 repeats), of which there were 19 (19/193, 9.8%) positive, 7 indeterminate (7/193, 3.6%), and 167 (167/193, 86.7.%) negative for CS. The SUVmax of PET-positive myocardial lesions ranges from 3.4 to 12.5, whereas mediastinal blood pool SUVmean ranges from 1.1 to 3.6. The indeterminate rate was significantly lower in group 2 compared with group 1 (P < 0.001). Conclusions: The prolonged 72-hour HFHPVLC diet preparation protocol successfully suppressed physiological myocardial FDG uptake and may permit a more sensitive and accurate method of diagnosing active CS using FDG PET/CT.