Cardiac MRI and FDG-PET in the diagnosis of cardiac sarcoidosis
Journal of Cardiovascular Magnetic Resonance volume 16, Article number: P299 (2014)
Sarcoidosis is a multisystem disorder with cardiac involvement in 25% of cases . Diagnosis of cardiac sarcoidosis is challenging with FDG-PET and cardiac MRI (CMRI) proving most reliable. We compare FDG-PET and CMRI with delayed enhancement (LGE) in patients with biopsy proven extra-cardiac sarcoidosis being investigated for cardiac involvement.
30 patients meeting Japanese Ministry of Health & Welfare guidelines  for clinical cardiac sarcoidosis were investigated with FDG-PET CT (Gemini TF Philips) and CMRI (Aera 1.5T Siemens) on the same day. Patients undergoing FDG-PET followed a 24 hour low-carbohydrate diet and overnight fast . CMRI examination included SSFP assessment of left ventricular (LV) function, short axis T2-weighted STIR and PSIR-LGE 10 minutes post 0.2 mmol/kg GdDTPA. Images were reviewed by experienced readers blinded to the results of the other examination. FDG-PET was considered positive if any segment (AHA 17 segment model) had an SUVmax > 3.6 (3). CMRI was considered positive if any segment showed 'sarcoid-type' LGE. In no case was edema present on STIR imaging without LGE in the same segment on subsequent PSIR.
FDG-PET and CMRI were positive in 10 patients; FDG-PET +ve and CMRI -ve in 3; FDG-PET -ve and CMRI +ve in 4; both -ve in 13. Distributions of FDG and LGE throughout the myocardium are summarized in Figure 1. In 2 cases where FDG and CMRI were +ve, LGE was in an ischemic pattern and both patients had known recent iscemic events (sub-endocardial). 6 of the remaining 8 had impaired LV function (EF < 50%). All FDG +ve/CMRI -ve cases had intense mediastinal/lung FDG uptake. All 4 FDG -ve/CMRI +ve had either long-standing sarcoidosis ( > 2 years) or absent node/lung FDG activity. Seven of the cases, -ve by both modalities, had no significant or minimal node/lung FDG uptake (SUVmax < 2.5).
Previous single modality studies have suggested sensitivity and specificity for FDG-PET of 89% and 78% and CMRI of 75% and 77% respectively. In our study, 43% showed no cardiac sarcoidosis by either modality and half of these had minimal or no FDG-PET evidence of active sarcoidosis elsewhere. Are these false -ve FDG-PET/CMRI studies or are the clinical criteria too sensitive? Our findings suggest FDG-PET and CMRI-LGE show different degrees of cardiac sarcoid involvement: FDG-PET indicating active inflammatory disease, LGE showing severe edema and scar. Those patients with LGE and no myocardial FDG uptake appear to have 'burnt-out' disease.
Iwai : Sarcoidosis. 1994
Hiraga : Japanese Ministry of Health & Welfare. 1993
Coulden : Eur Radiol. 2012
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Coulden, R., Jones, H., Sonnex, E. et al. Cardiac MRI and FDG-PET in the diagnosis of cardiac sarcoidosis. J Cardiovasc Magn Reson 16 (Suppl 1), P299 (2014). https://doi.org/10.1186/1532-429X-16-S1-P299