Quantitative Interpretation of FDG PET for Cardiac Sarcoidosis Reclassifies Visually Interpreted Studies and Potentially Reduces Unnecessary Downstream Interventions

Objectives: Quantitative interpretation of FDG PET/CT imaging for cardiac sarcoidosis (CS) predicts events and response to immunosuppression, and it may be more specific for CS than visual (qualitative) interpretation. However, most FDG PET imaging is interpreted visually. We aimed to evaluate whether re-analysis of FDG uptake using quantitative interpretation of initially visually interpreted FDG PET/CT images could potentially have reduced unnecessary downstream interventions (ICD placement and immunosuppression initiation/increase).

Methods: FDG PET/CT studies for the evaluation of cardiac sarcoidosis (N=162 studies; 132 patients, 63 fulfilling JMHW or HRS CS criteria) obtained from November 2013 to October 2015 were retrospectively re-analyzed. Quantitative analysis for FDG uptake using standardized uptake values (SUVs) was compared to the interpretation from the initial clinical report, which had been performed at the time of the exam by experienced readers using traditional visual qualitative analysis. Net reclassification indices for study FDG positivity were calculated, and events data (admissions for arrhythmia and CHF, ICD placement after report, immunosuppression initiation or dose increase after report, and deaths) was analyzed with respect to reclassification of FDG positivity.

Results: Out of 154 interpretable studies, 72 (47%) were initially clinically reported as visually “FDG positive”. Quantitative analyses using a 1.5X left ventricular blood pool (LVBP) SUV threshold for study positivity resulted 22/72 (31%) of these studies being reclassified as “quantitatively negative”, while only 2/82 (2%) were reclassified from “visually negative” to “quantitatively positive”. This resulted in a -13.0% net reclassification of FDG positivity compared to the initial clinical report. Average SUVMax was significantly greater (5.5 ± 0.3 g/ml; P=0.001) in studies with congruent quantitative and initial report positivity (N=50), compared to 2.3 ± 0.2 g/ml in the quantitatively negative/report positive group (N=22). In the quantitatively negative but report positive group (“false positives”), 4 patients had ICDs placed and immunosuppression was initiated or the dose increased in 7 patients. Only 2 (9%) patients in this group had an arrhythmia or CHF in comparison to 12 (23%) in the quantitatively (“true”) positive patients.

Conclusion: Re-interpretation of FDG PET/CT imaging for cardiac sarcoidosis using quantitative techniques lead to a nearly 1/3 of visually “FDG positive” studies being reclassified as normal (no FDG uptake). In 7/22 patients that were reclassified as normal, initiation or increase of immunosuppression could potentially have been avoided, thus possibly limiting toxicities of these medications. The adverse event rate for arrhythmias and CHF in patients reclassified as normal was low. This suggests quantitative interpretation of FDG PET/CT for CS could reduce unnecessary immunosuppressive treatment in some patients. Research Support: None