FDG PET for Cardiac Sarcoid
A 56-year-old female patient with no relevant prior medical history presented to the emergency department with sustained monomorphic ventricular tachycardia (VT). After cardioversion, she developed 3rd degree atrioventricular (AV) block requiring transvenous pacing. During admission, coronary angiography was performed and normal coronaries were found. A cardiac magnetic resonance imaging (MRI) was done and showed decreased left ventricular systolic function with hypokinesia of the anteroseptal, inferoseptal, and inferior walls and subepicardial and mid left ventricle (LV) wall areas of late gadolinium enhancement (LGE) in the anteroseptal, inferoseptal, inferior, and anterolateral walls, consistent with nonischemic regions of fibrosis (Figure 1).
Given the MRI results as well as the history of VT followed by 3rd degree AV block, a fluorodeoxyglucose (FDG) positron emission tomography (PET) (cardiac and whole body) scan was subsequently performed and showed a mismatch between perfusion and metabolic imaging to further confirm the diagnosis and provide an imaging reference for future follow-up. FDG images demonstrate intense focal uptake in the basal and mid segments of the inferior, inferoseptal, and anteroseptal walls and also moderate uptake in the RV free wall. Rest images with Rubidium-82 showed perfusion defects in the same segments, suggesting areas of scar (or impaired perfusion caused by microvascular compression, likely due active inflammation). The gated images showed a moderate to severe reduction (32%) of the LV ejection fraction (LVEF) (Figure 2). The whole body FDG PET scan showed multiple FDG-avid lesions in the lungs, mediastinal and hilar lymph nodes, as well as in the lumbar spine, iliac wings, and ribs that were compatible with active systemic inflammatory disease.
An endomyocardial biopsy (EMB) was performed and revealed non-caseating granuloma. The diagnosis of cardiac and extra-cardiac sarcoidosis (CS) was made. A pacemaker/implantable cardiac defibrillator (ICD) was implanted, and immunosuppressive therapy was initiated with prednisone 50 mg daily. The patient was discharged and followed as an outpatient in a CS clinic.
Six months later, follow-up FDG PET imaging was performed and showed improvement in the LVEF (32-42%) and in the perfusion images (inferior and septal segments) as well as significant decrease in myocardial FDG uptake. The whole body scan showed interval resolution of FDG-avid mediastinal and hilar lymphadenopathy and no evidence of extra-CS. At that time, the patient had no cardiac complaints, and the steroid dose was tapered (Figure 3).
On follow-up at 21 months, device interrogation showed runs of nonsustained VT and paroxysmal atrial fibrillation. LVEF had improved to 51%. At 26 months, the patient had an appropriate ICD shock for polymorphic VT. One month later, another appropriate shock occurred. Medical therapy was adjusted. Subsequently, the patient has had no cardiac symptoms for 1 year and no VT on interrogation of her ICD (Figure 4).
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