Assessing bone (marrow) involvement in sarcoidosis using F18-FDG PET/CT

Objectives The incidence of bone involvement in sarcoidosis is not obvious. Previous studies, based on morphologic imaging, suggest an incidence of 2-3%, most frequently affecting the phalanges. Till now the usefulness of PET/CT in detection of osseous involvement has not been evaluated. The aim of this study was to determine the frequency and distribution pattern of bone and bone marrow involvement as detected by PET/CT in sarcoidosis patients.

Methods Between June 2006 and September 2010, 123 patients suffering from severe sarcoidosis underwent a PET/CT scan. Of these 123 patients 94 (76%) had PET-positive findings associated with sarcoidosis. Subsequently, these 94 PET/CT scans were screened for the presence of bone or bone marrow localisations. All low-dose CT scans were examined by an experienced musculoskeletal radiologist to exclude other causes of enlarged bone uptake.

Results In 32 (34%) of the 94 patients, PET positive bone or bone marrow localisations were present. Sixty % (19/32) showed obvious focal bone lesions at various locations: axial skeleton (47%), pelvis (40%), extremities (34%), and skull (2%)). In 40% (13/32) diffuse enlarged uptake in both the axial and peripheral bone marrow, without focal lesions were found. Both diffuse and focal uptake was seen in 34% (11/32), whereas in 25% (8/32) only focal lesions. In all but 2 (6%) patients no bone-abnormalities on low dose CT were found.

Conclusions A substantial number (34%) of PET/CT positive sarcoidosis cases had osseous sarcoidosis features on PET/CT, 26% (32/123) of all studied patients. This is far more as could be expected from previous literature. The majority of these lesions (94%) could not be detected on low dose CT. There was no single location of preference. These preliminary results stress the importance of functional PET-imaging as a sensitive tool to investigate bone involvement in sarcoidosis