Introduction: Sarcoidosis is a systemic disease with distinct clinical phenotypes associated with varying degrees of organ involvement. [18F]FDG PET/CT allows for the assessment of the location and activity of inflammation.
Objectives: Attempt to identify organ involvement and identify PET phenotypic patterns of sarcoidosis based on FDG PET imaging
Materials and Methods: Carb-free [18F]FDG PET/CT whole-body scans were performed in 90 steroid naïve patients diagnosed with sarcoidosis. PET/CT images were qualitatively analyzed to assess the presence of active organ lesions with particular attention to cardiac involvement. A dominant phenotype based on organ involvement revealed by metabolic activity was determined in each patient. It was assumed that phenotypes may overlap, therefore an individual patient could be assigned to more than one phenotypic group.
Results: In 15/90 patients, no active lesions were detected. In 20 cases, active lesions were limited to the lungs and mediastinum; in the remaining cases, multi-organ involvement was observed. Seven patterns of organ involvement (PET phenotypes) could be identified: rheumatological (11), laryngological (10), parenchymal (11), nodal (9), hematological(16), pulmonary (20), and isolated cardiac (5) In 10 cases, phenotypic overlap was detected. Cardiac activity was seen in 30 patients - isolated in 5 and with multi-organ involvement in the remaining 25 patients, with a considerable variety in the level of metabolic activity.
Conclusions: We were able to identify distinct [18F]FDG PET/CT phenotypes of sarcoidosis. Cardiac uptake was variable, what may have implied either sarcoidosis infiltrates or other nonspecific lesions including both pathological conditions and inadequate patient preparation. We postulate that [18]FDG PET may identify distinct sarcoidosis phenotypes, however these finding needs to be translated to clinical practice to enhance therapeutic decisions. Detected cardiac abnormalities should be interpreted with caution. Further relation between distinct [18F]FDG PET/CT patterns and clinical phenotypes of sarcoidosis will be investigated.