Metastatic Lung Adenocarcinoma Mimicking Miliary Tuberculosis: A Case Report.

Lung adenocarcinoma (LA) can present with a wide range of morphological patterns and may mimic disseminated infectious diseases such as miliary tuberculosis (TB), posing significant diagnostic challenges and potentially delaying appropriate treatment. We report a case of metastatic pulmonary adenocarcinoma that was initially misdiagnosed as miliary TB. A 35-year-old nonsmoking male presented with a progressive dry cough and shortness of breath. Chest imaging revealed diffuse bilateral micronodules and a pericardial effusion, raising suspicion for miliary TB. Although acid-fast bacilli smears and a purified protein derivative test were negative, empiric anti-TB therapy was initiated based on radiographic findings. Despite treatment, the patient's condition deteriorated. Further evaluation, including a cervical lymph node biopsy, unexpectedly revealed metastatic, moderately differentiated adenocarcinoma of pulmonary origin. A subsequent pericardial biopsy confirmed metastatic involvement. Anti-TB therapy was discontinued; however, the patient's clinical status continued to decline. This case highlights the diagnostic challenge of metastatic LA mimicking miliary TB. In low TB-burden settings, it is essential to maintain a broad differential diagnosis and to consider alternative etiologies, such as metastatic malignancies, when confronted with miliary patterns on chest imaging, particularly in the absence of classic TB risk factors or poor response to treatment. Tissue biopsy from accessible sites and immunohistochemistry remain critical for establishing an accurate diagnosis and guiding appropriate management in such complex presentations. This case underscores the limitations of relying solely on imaging and reinforces the need for a thorough diagnostic workup when evaluating diffuse micronodular lung patterns.