A Case of Metastatic Lung Adenocarcinoma, With Metastasis to the Brain, Spleen, Liver, and Bone, Mimicking Sarcoidosis.

Lung adenocarcinoma can radiologically and clinically mimic granulomatous disease, leading to diagnostic delays. Bilateral hilar and mediastinal lymphadenopathy, perilymphatic nodules, and partial corticosteroid responsiveness may anchor clinicians to a diagnosis of sarcoidosis. This case highlights the importance of maintaining a broad differential and pursuing a timely, tissue-based diagnosis when features evolve atypically. We report a previously healthy 49-year-old male, lifelong non-smoker, who presented with three months of progressive multisystem symptoms, including exertional dyspnea, nocturnal cough, constitutional complaints, neuropathic pain, visual auras, and intermittent paresthesia. Imaging revealed diffuse thoracic lymphadenopathy, pulmonary fibrosis, splenic and adrenal nodules, and multifocal enhancing brain lesions, while positron emission tomography (PET)-computed tomography (CT) demonstrated widespread fluorodeoxyglucose (FDG)-avid disease. Although sarcoidosis and infective granulomatous conditions were initially considered, a cervical lymph-node biopsy confirmed metastatic lung adenocarcinoma (stage IV). This case illustrates how radiologic mimicry and anchoring bias can delay the recognition of malignancy, emphasizes the non-specific nature of FDG avidity, and underscores the decisive role of histological confirmation. Early consideration of malignancy in "sarcoid-like" presentations, especially when systemic features or incomplete steroid response arise, is essential to ensure timely oncologic therapy and integration of supportive care.