Multisystem FDG-avid sarcoidosis with osseous involvement mimicking disseminated metastatic malignancy

Sarcoidosis may closely mimic disseminated malignancy on FDG-PET/CT because active granulomatous inflammation can demonstrate intense multisystem FDG uptake. We report a 59-year-old woman with previously diagnosed pulmonary sarcoidosis who presented with acute dyspnea and right leg pain and was found to have segmental and subsegmental pulmonary emboli on CT pulmonary angiography. FDG-PET/CT demonstrated extensive intensely hypermetabolic mediastinal, hilar, abdominal and pelvic lymphadenopathy with pulmonary, hepatic, splenic and multifocal osseous involvement, including a right iliac lesion (SUVmax 12.3), raising strong suspicion for disseminated metastatic malignancy or lymphoproliferative disease. CT-guided biopsy of the iliac lesion revealed non-necrotizing granulomatous inflammation without evidence of malignancy or infection, confirming multisystem sarcoidosis with osseous involvement. This case highlights the importance of histological confirmation when FDG-PET/CT findings in sarcoidosis mimic metastatic disease.