Sarcoidosis Mimicking Metastatic Disease: Multisystem Involvement With Osseous Manifestations.

Sarcoidosis is a chronic granulomatous disease of unknown etiology that can affect multiple organs, most frequently the lungs, lymph nodes, skin, and eyes. Osseous involvement is a rare manifestation, typically affecting small bones, although axial skeleton lesions may also occur. We report the case of a 42-year-old woman with no relevant past medical history who presented with fatigue, night sweats, diffuse joint pain, and low back pain. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography demonstrated multiple hypermetabolic pulmonary nodules, predominantly in the right upper lobe, associated with bilateral hilar, mediastinal, and supraclavicular lymphadenopathy, as well as focal uptake in the right iliac bone, sacrum, and L4 vertebral body. Given the imaging pattern and metabolic activity, disseminated malignancy was initially suspected. Histopathological examination of mediastinal lymph node and iliac bone biopsies revealed noncaseating granulomatous inflammation. Laboratory results showed elevated serum angiotensin-converting enzyme, negative interferon-gamma release assay, and negative autoimmune serologies. Following a multidisciplinary discussion, a diagnosis of sarcoidosis was established. The patient was treated with systemic corticosteroids followed by methotrexate, with significant clinical improvement. This case highlights an uncommon presentation of multisystemic sarcoidosis with axial skeletal involvement and imaging findings mimicking metastatic disease, underscoring the importance of histological confirmation and multidisciplinary assessment in establishing an accurate diagnosis and guiding management.