B80-5-36 Fulminant Metastatic Lung Adenocarcinoma Masquerading as Miliary Tuberculosis

Abstract Introduction Miliary tuberculosis (TB) remains a leading cause of diffuse micronodular lung disease, particularly in endemic areas. However, metastatic malignancies, most notably lung adenocarcinoma, may rarely mimic this radiographic appearance. Distinguishing these entities is essential, as management and prognosis differ profoundly. We present a case of stage IV lung adenocarcinoma with diffuse pulmonary, pericardial, cerebral, and osseous involvement initially treated as miliary TB in a young adult from Guatemala. Case Description A 30-year-old previously healthy man from Central America presented with progressive weakness, fatigue, weight loss, cough productive of sputum, and bilateral lower extremity pain. Chest CTA demonstrated a large pericardial effusion, diffuse bilateral pulmonary opacities, and lytic bone lesions suggestive of disseminated infection versus metastatic disease. Given the miliary pattern, empiric RIPE therapy was initiated for presumed miliary TB. QuantiFERON testing subsequently returned negative, prompting discontinuation of anti-tubercular therapy. Pericardiocentesis cytology revealed malignant adenocarcinoma cells consistent with a primary pulmonary origin. Brain MRI showed multiple metastatic lesions, and orthopedic surgery performed bilateral internal fixation to prevent pathological fractures. During hospitalization, the patient developed tachycardia, hemoptysis, and fever. Chest imaging revealed worsening diffuse infiltrates despite broad-spectrum antibiotics (piperacillin-tazobactam and vancomycin). He progressed to acute hypoxemic respiratory failure requiring intubation and ICU transfer. Bronchoscopy revealed diffuse pulmonary hemorrhage with an endobronchial mass, confirming advanced malignant spread. Given poor prognosis, the palliative care team was consulted, and the patient elected to change code status to DNR and pursue comfort-focused measures. Discussion This case underscores the diagnostic challenge posed by metastatic adenocarcinoma presenting with a miliary pattern, especially in a young adult from an endemic region without traditional lung cancer risk factors. Radiologically, diffuse micronodular opacities classically suggest miliary TB, but malignant etiologies such as hematogenous metastases from adenocarcinoma, thyroid, or renal primaries should be considered when atypical features coexist. The presence of lytic bone lesions, pericardial effusion, and negative tuberculosis testing are critical diagnostic clues favoring malignancy. Histopathologic confirmation remains the cornerstone for accurate diagnosis. Delay in recognizing malignant mimics of miliary TB can result in unnecessary anti-tubercular therapy, delayed oncologic intervention, and missed opportunities for timely palliative care. Additionally, this case highlights the increasing incidence of lung cancer in younger, nonsmoking adults, raising awareness of the need for high suspicion in atypical presentations. Maintaining a broad differential diagnosis for diffuse pulmonary infiltrates is imperative, as early tissue diagnosis can profoundly impact management, prognosis, and patient-centered decision-making. This abstract is funded by: None