Tuberculous Pericardial Effusion Mimicking Malignant Pericardial Disease in a Patient With Metastatic Duodenal Neuroendocrine Tumor.

Tuberculous pericarditis remains an important differential diagnosis for pericardial effusion in tuberculosis-endemic regions, even in patients with established malignancy. We report a 55-year-old female diagnosed with a metastatic well-differentiated Grade 1 duodenal neuroendocrine tumor with hepatic and nodal metastases based on gallium-68 DOTATOC positron emission tomography/computed tomography, histopathology, and immunohistochemistry findings. Transthoracic echocardiography revealed a large circumcardiac pericardial effusion that was initially presumed to be malignant because of the underlying metastatic disease. Diagnostic pericardiocentesis demonstrated a lymphocyte-predominant exudative effusion with negative cytology for malignant cells. Although pericardial fluid adenosine deaminase (ADA) levels were low, Xpert Mycobacterium tuberculosis/rifampicin assay detected Mycobacterium tuberculosis complex with rifampicin sensitivity, establishing the diagnosis of tuberculous pericardial effusion. The patient was treated with anti-tubercular therapy, adjunctive corticosteroids, and somatostatin analog therapy with close liver function monitoring. This case highlights the diagnostic challenge of differentiating tuberculous and malignant pericardial effusion in oncology patients and emphasizes that low ADA levels do not exclude tuberculous pericarditis. Comprehensive microbiological evaluation, including molecular diagnostic testing, remains essential for accurate diagnosis in tuberculosis-endemic regions.