Prognostic value of hypermetabolic bone sarcoidosis observed by ¹⁸F-fluorodeoxyglucose positron emission tomography

Objectives: Sarcoidosis is a multisystemic granulomatosis diagnosed mainly in young adults. F-18-fluorodeoxyglucose (F-18-FDG) PET/CT is useful in sarcoidosis cases to search for a biopsiable site or assess disease activity.F-18-FDG PET/CT can reveal bone hypermetabolism in sarcoidosis patients, even in the absence of osteoarticular symptoms. The aim of this study was to describe metabolic bone involvement in sarcoidosis patients and to evaluate its prognostic impact. Methods: This was an observational, comparative, retrospective, monocentric study. Inclusion criteria were a confirmed diagnosis of sarcoidosis according to the World Association of Sarcoidosis and Other Granulomatous Diseases (WASOG) criteria and at least one F-18-FDG PET/CT scan during follow-up. Metabolic bone involvement of sarcoidosis was defined as focal bone hypermetabolism with no argument for a differential diagnosis of bone F-18-FDG uptake. Patients with and without bone involvement were compared. Results: Among the 175 included patients, 32 (18%) had metabolic bone involvement of sarcoidosis. The metabolic bone involvement was mainly axial and mostly without bone abnormalities on CT. Metabolic bone involvement was associated with intrathoracic and extrathoracic lymph node involvement and with a greater number of organs involved. Patients with metabolic bone involvement more frequently received corticosteroids, methotrexate and TNF-alpha inhibitors and a greater number of treatments. Relapse of sarcoidosis occurred sooner in patients with metabolic bone involvement. Conclusion: These results suggest that metabolic bone involvement is associated with more diffuse and more severe sarcoidosis.