Unsuspected skeletal sarcoidosis mimicking metastatic disease on FDG positron emission tomography and bone scintigraphy

Sarcoidosis is a disease process of unknown cause that exhibits heterogeneous clinical manifestations. Although the mediastinum and lungs are most commonly involved, the granulomatous process may also affect the skeleton, skin, eyes, kidneys, spleen, and liver. A 51-year-old woman with low back pain and no history of cancer was found to have a suspicious lesion at L4 on magnetic resonance imaging. Findings of bone scintigraphy were consistent with multiple metastases, and computed tomography of the chest identified two small indeterminate pulmonary nodules. Similarly, findings of fluorodeoxyglucose positron emission tomography were consistent with widespread skeletal metastases, but a primary tumor was not identified. Biopsy of a left femur lesion was diagnostic of active sarcoidosis with no evidence of cancer.