Scadding revisited: a proposed staging system for cardiac sarcoidosis.

important problem. While autopsy findings suggest that up to 25% of patients with sarcoidosis (1) may have myocardial granulomas, only about 5% (2) of American patients with sarcoidosis manifest symptomatic cardiac disease. Cardiac involvement may result in heart block, wall motion abnormalities, cardiomyopathy, and malignant arrhythmias, all of which may adversely impact quality of life and survival (3). Since fatal arrhythmia/sudden death or cardiomyopathy may be the first manifestation of myocardial involvement (4, 5) there is interest in early identification and more precise diagnosis of cardiac sarcoidosis (CS). Advanced imaging modalities, including cardiac positron emission tomography (PET) and cardiac magnetic resonance (CMR), have emerged as critically important tests by which cardiac sarcoidosis can be identified and prognosis determined. Both modalities can image inflammation and fibrosis – the two key distinctive features of CS. PET can identify active sarcoid inflammation by means of 18-fluorodexoyglucose (FDG) uptake and fibrosis by means of Rubidium-82 (Rb-82) or Nitrogen-13 (N-13) myocardial perfusion imaging defects. CMR can identify inflammation be means of T2-weighted imaging and fibrosis by means of late gadolinium enhancement (LGE).Data comparing the diagnostic accuracy of PET vs. CMR in CS are not well developed, while data supportive of the clinical utility of each modality in isolation has been widely reported. There is no consensus upon which test is superior, with modality choice usually dependent upon institutional availability and local expertise. Data suggest that PET imaging with FDG may be more sensitive than CMR imaging for detection of myocardial inflammation in sarcoidosis, in part due to the limited reproducibility and challenge of interpretation of T2 weighted CMR imaging (6, 7). As an example, one report presented a patient in whom an initial CMR was negative while PET showed evidence of inflammation by FDG,whereas a year laterMRI showed delayed enhancement in the area previously shown to have FDG uptake on PET (8). Conversely, CMR with late gadolinium enhancement (LGE) imagingmay bemore specific for the identification of the myocardial fibrosis that can develop following granulomatous inflammation and LGE appears to predict adverse clinical outcomes including death or arrhythmic events, whereas absence of CMR-LGE appears predictive of low risk (9, 10). Despite abundant data for both modalities, there is little published guidance as to which test (CMR or PET) to use in which clinical setting and no consensus of how to report PET findings.The purpose of this document is to propose a structure for the classification of cardiac sarcoidosis using PET imaging, so as to establish a standardization of reporting for both clinical and research applications and allow for future comparison to CMR (Table 1, Figure 1).This is important in order to frame more robust comparative studies between CMR Scadding revisited: a proposed staging system for cardiac sarcoidosis based on advanced imaging