FDG PET Positive Cardiac Amyloidosis

Abstract

Background Cardiac positron emission tomography (PET) is routinely utilized to diagnose cardiac sarcoidosis, but may be positive in other cardiac conditions that result in myocardial inflammation. ATTR cardiac amyloidosis, an infiltrative disease that causes atrial arrhythmias and heart failure, is not typically thought to present with an inflammatory process. However, we observed four cases in which 18F-flurodeoxyglycose (FDG) PET scan findings were suspicious for cardiac sarcoidosis, but right ventricular endomyocardial biopsy (RV EMB) pathology specimens revealed ATTR wild-type (ATTRwt) cardiac amyloidosis. Methods Retrospective chart review was performed on patients with a positive cardiac FDG PET scan who also had a concomitant diagnosis of ATTR cardiac amyloidosis at Mayo Clinic Rochester between January 1, 2000 and March 24, 2019. Results Four patients with clinical presentation suggestive of cardiac sarcoidosis had positive FDG PET scans but were found to have biopsy-proven ATTRwt cardiac amyloidosis. All four patients were male with an average age of 71 years (62, 75). Two patients presented with ventricular arrhythmias and had transthoracic echocardiograms that were not suggestive of cardiac amyloidosis. FDG PET scans of these two patients revealed myocardial FDG uptake, similar to what can be seen in cardiac sarcoidosis. Both patients underwent RV EMB, with pathology specimens and mass spectrometry revealing ATTRwt cardiac amyloidosis. One of these two patients had a positive nuclear 99mTechnetium-pyrophosphate (PYP) scan (H/Cl ratio 1.9) and the other had a negative PYP scan (H/CL 1.2). The third patient, with a history of biopsy proven pulmonary sarcoidosis, presented with atrial fibrillation and conduction abnormalities. FDG PET scan revealed myocardial perfusion defects and patchy FDG uptake, but RV EMB revealed ATTRwt cardiac amyloidosis. Nuclear PYP was positive (H/Cl ratio of 1.8). The fourth patient presented with intermittent high grade AV block and underwent pacemaker implantation. He later developed frequent monomorphic premature ventricular contractions. Cardiac FDG PET scan illustrated FDG uptake, but the concurrent CT trunk did not illustrate any FDG uptake suspicious for extra-cardiac sarcoidosis. RV EMB was consistent with ATTRwt cardiac amyloidosis, but PYP was negative. Discussion These findings suggest that inflammation could play a role in ATTR cardiac amyloidosis. We have previously seen inflammatory changes of lymphohistiocytic infiltration around areas of amyloid protein deposition on biopsy specimens in ATTR cardiac amyloidosis. The role of therapy targeted at stabilizing transthyretin versus immunosuppressive agents in this subgroup remains unclear.