LAUSR

Background: Myeloid Sarcoma (MS) are tumors containing myeloid blasts occurring in a location other than the bone marrow, including lymph nodes, skin, and soft tissues. MS presenting as polyserositis however is very rare, with only a few cases in the literature. Case Report: A 20-year-old male presented with cough, shortness of breath and was found to have left upper lobe consolidation, left pleural effusion, pericardial effusion, and a large anterior mediastinal mass. A transthoracic echocardiogram showed pericardial effusion with tamponade physiology. He underwent emergent pericardiocentesis and thoracentesis. The fluid studies showed flow cytometry findings consistent with MS/ acute myeloid leukemia (AML) phenotype. A bone marrow aspirate and biopsy were unremarkable and showed no immunophenotypic findings diagnostic of acute leukemia or a lymphoproliferative disorder. Cytogenetics was negative for AML abnormalities per FISH analysis. Videoassisted thoracoscopy surgery (VATS) with biopsy of the mediastinal mass, pericardium, and left upper lobe of the lung was consistent with MS. He was treated with induction cytarabine and idarubicin, and a follow up PET-CT scan showed complete remission. He is currently day 200 + post stem cell transplant with no evidence of disease recurrence. Conclusion: To the best of our knowledge, this is the first case of isolated myeloid sarcoma presenting as polyserositis, without prior leukemia/ bone marrow involvement. Hence, fluid studies should involve cytometry analysis and MS should be entertained as a differential for polyserositis, even without a history of prior leukemia. Timely diagnosis can expedite aggressive chemotherapy required for a potentially life-threatening disease.