Unmasking Sarcoidosis: Fever and Arthralgia Revealing an Underlying Granulomatous Disease

Sarcoidosis is a multisystem granulomatous inflammatory disease of unknown etiology, with a highly variable clinical presentation. Diagnosis can be particularly challenging, as the condition may manifest through a wide range of nonspecific symptoms, involve multiple organs, and lack pathognomonic findings. We describe the case of a previously healthy 65-year-old man who presented to the emergency department with fever and inflammatory large-joint arthralgias, without other associated symptoms. Physical examination was unremarkable, with no palpable lymphadenopathy, rash, or inflammatory signs in any joints examined. Initial laboratory evaluation showed a cholestatic pattern of liver enzymes, increased C-reactive protein, and elevated angiotensin-converting enzyme. Chest computed tomography (CT) revealed mediastinal-hilar lymphadenopathy. During hospitalization, the patient maintained a persistent fever and arthralgias, prompting further evaluation with 18F-fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET-CT), which demonstrated symmetric FDG uptake in thoracic lymph nodes and peripheral joints. Given the unexplained cholestatic pattern, a liver biopsy and lymph node biopsy were performed; there were no findings compatible with granulomas or malignancy. After excluding infectious, autoimmune, and neoplastic causes, the hypothesis of sarcoidosis persisted even with no definitive histological support, and the diagnosis was made through bronchoalveolar lavage (BAL), which revealed lymphocytic inflammation with a CD4/CD8 ratio of 7.3, highly compatible with sarcoidosis. Corticosteroid therapy was initiated with an excellent clinical response. This case highlights the importance of a systematic and comprehensive diagnostic approach when evaluating prolonged fever and inflammatory arthralgias. It underscores the need to consider sarcoidosis, even as a diagnosis of exclusion, particularly in atypical presentations with predominant joint involvement.