SESSION TITLE: Medical Student/Resident Lung Pathology SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: Miliary nodules are randomly dispersed pulmonary micronodules found on chest radiograph and CT imaging that can be the manifestation of many diseases, carrying a broad differential based on imaging alone. While an infectious process is most likely, it is important to avoid anchoring on a single diagnosis with this finding, especially in the face of inconclusive data. CASE PRESENTATION: A 49-year-old male nonsmoker with past medical history of hypertension, hyperlipidemia, diabetes mellitus, and stable ulcerative colitis presented to the Emergency Room from his primary care physician’s office with a 3-week history of cough, dyspnea on exertion and a chest x-ray concerning for diffuse airspace disease. He denied fevers, chills, or night sweats, but endorsed unintentional weight loss. He has had extensive international travel, and most recently traveled to England and Vietnam, where he was in predominantly urban areas. On arrival, he was afebrile, hemodynamically stable, but hypoxemic on room air. Chest CT demonstrated diffuse pulmonary nodular opacities in a miliary pattern bilaterally with a 1.7 cm cavitary lesion in the LUL. He was admitted and placed in airborne isolation amid concern of miliary tuberculosis. BAL on day 2 of multiple lung zones was performed. Mtb PCR and AFB smears were negative for tuberculosis, but positive for PCP PCR in only one LUL sample. His respiratory symptoms persisted despite antibiotic therapy; he was not started on anti-tuberculoid therapy. VATS was then performed, and tissue biopsies revealed non-small cell lung carcinoma with bilateral pulmonary metastases. Pathology and genotyping demonstrated poorly differentiated HER2+/EGFR- lung adenocarcinoma. DISCUSSION: We describe a middle-aged nonsmoking male with a subacute cough and progressive dyspnea in the setting of extensive international travel and randomly dispersed pulmonary micronodules on CT. Miliary pattern is thought to be due to hematogenous spread of disease. In areas where tuberculosis is endemic, image findings can often be diagnostic, however these must be differentiated from centrilobular or perilymphatic patterns of distribution. While this presentation had several features suspicious for miliary tuberculosis, BAL Mtb PCR specimens were negative, forcing reconsideration of non-infectious etiologies. Rapid evaluation by VATS tissue biopsy diagnosed primary lung adenocarcinoma with pulmonary metastasis. The data on genotyping intrapulmonary carcinomatosis as a means of further characterization is still growing, and the HER2+ mutation is found in only 1% of non-small cell lung cancers. CONCLUSIONS: This case represents the importance of rapid testing, without premature diagnostic closure for distinguishing two potentially fatal, but treatable diseases such as miliary tuberculosis and poorly differentiated HER2+ lung adenocarcinoma. Reference #1: Walker C, Abbott G, Greene R, Shepard JA, Vummidi D, Digumarthy S. Imaging Pulmonary Infection: Classic Signs and Patterns. American Journal of Roentgenology (2014);202: 479-492. DISCLOSURES: No relevant relationships by Irmgard Behlau, source=Web Response no disclosure on file for Augustin Delago; No relevant relationships by Joseph Khoory, source=Web Response No relevant relationships by David Miller, source=Web Response No relevant relationships by MARIANA STOLERU, source=Web Response