B80-6-17 Primary Lung Adenocarcinoma Mimicking Miliary Tuberculosis Pattern: A Rare Presentation

Abstract Introduction Lung adenocarcinoma, the most common subtype of non-small cell lung cancer (NSCLC), typically presents as a solitary peripheral nodule or ground-glass opacity. Rarely, it manifests with diffuse micronodular infiltrates mimicking miliary tuberculosis (TB) or fungal infections, posing a diagnostic challenge. We describe a case of primary lung adenocarcinoma initially suspected to be miliary TB due to its radiographic appearance. Case Presentation A 48-year-old woman with a history of deep vein thrombosis on apixaban and prior incarceration presented with one week of progressive dyspnea and nonproductive cough. She denied fever, weight loss, or night sweats. Chest X-ray and CT imaging (Figure-1 and 2) revealed innumerable bilateral pulmonary nodules and a left pleural effusion, suggestive of miliary TB or sarcoidosis. She had a 17-year smoking history (quit seven years prior) and reported daily marijuana use. QuantiFERON-TB Gold and PPD testing were negative. Pleural fluid cytology was exudative (Figure -3 and Table-1), and video-assisted thoracoscopic surgery (VATS) with pleurodesis confirmed primary lung adenocarcinoma. MRI of the brain demonstrated multiple enhancing lesions consistent with metastases. The patient began systemic chemotherapy following port placement and was discharged home in stable condition. Discussion Adenocarcinoma presenting with a miliary pattern is uncommon and often misdiagnosed as infection. The radiographic similarity arises from hematogenous dissemination of malignant cells producing diffuse micronodules. Unlike miliary TB, such patients may lack constitutional symptoms, and TB testing is negative. Histopathology and immunohistochemistry remain essential for definitive diagnosis. Previous reports describe this pattern in association with EGFR mutations, which may predict responsiveness to tyrosine kinase inhibitors. Brain metastases, as in this case, indicate advanced disease and portend poor prognosis. The evolving use of PD-1/PD-L1-targeted immunotherapy and molecular profiling offers improved survival in selected patients. Conclusion Miliary-pattern pulmonary nodules should not be presumed infectious, especially in patients without systemic symptoms or with smoking history. Early tissue diagnosis through biopsy and immunohistochemical analysis is critical to distinguish malignancy from infection and to initiate timely, targeted treatment. This case underscores the importance of maintaining a broad differential diagnosis when evaluating diffuse pulmonary nodules. This abstract is funded by: none