The logic and challenges of imaging sarcoidosis with whole body FDG PET

Excerpt

Sarcoidosis is an idiopathic systemic granulomatous disease that can affect multiple organs. The adjusted annual incidence among black Americans is roughly three times that among white Americans (35.5 cases per 100,000, as compared with 10.9 per 100,000).1 Sarcoid involvement of the lungs and/or heart can lead to significant morbidity and mortality. Even though cardiac sarcoidosis (CS) appears to be underdiagnosed clinically, it is considered the second leading cause of death by sarcoidosis in the United States and the leading cause in Japan.2,3 Inflammatory granulomas or post-inflammatory scarring may lead to conduction abnormalities, arrhythmias, sudden cardiac death, and congestive heart failure. CS frequency is debated, with an approximate incidence of 5% based on clinical assessment,4 27% in autopsy studies,5 and 39% in an imaging study that used cardiac MRI or PET.6 Obtaining ante-mortem diagnosis of cardiac sarcoidosis is challenging as the diagnostic gold standard, i.e., biopsy is invasive, subject to sampling error7 and has a sensitivity of only 20%–30%, because it misses the often patchy areas of cardiac involvement.1,8,9 Additionally, the criteria for the diagnosis of cardiac sarcoidosis from the Japanese Ministry of Health and Welfare (JMHW) have an imperfect diagnostic accuracy.10,11 Therefore, the diagnosis of cardiac sarcoidosis often relies on integrating both clinical and imaging findings, including those from advanced imaging modalities like cardiac MRI with gadolinium and FDG PET (latter most often combined with CT, i.e. PET-CT).7 While the typical delayed gadolinium enhancement seen on cardiac MRI represents sarcoid inflammation related cardiac damage and scarring, FDG uptake represents active inflammation. Both FDG PET and MRI provide high sensitivity for diagnosing cardiac sarcoidosis, but the specificity of cardiac MRI is better.12 Advantages of FDG PET include the biologic nature of the imaging signal, the ability to identify cardiac and extracardiac sarcoidosis involvement in one exam, feasibility of imaging patients with electrical/metallic devices and renal impairment, assessment of therapy response and risk stratification.7,13,14 …