Fluid Overload-Associated Large B-Cell Lymphoma Presenting as Isolated Pleural Effusion

Primary effusion-based lymphomas are uncommon and may pose significant diagnostic challenges. Fluid overload-associated large B-cell lymphoma is a recently recognized entity in the 5th edition of the World Health Organization Classification of Hematolymphoid Tumors and should be included in the differential diagnosis of effusion-based lymphomas, particularly in elderly immunocompetent patients with conditions that predispose to fluid overload. <b>Background and Clinical Significance:</b> We report a case of fluid overload-associated large B-cell lymphoma to add to the limited literature and highlight distinguishing features from other primary effusion lymphomas. <b>Case Presentation</b>: A 77-year-old male with end-stage renal disease on hemodialysis and heart failure with reduced ejection fraction was admitted for respiratory failure and found to have a right-sided pleural effusion. Two pleural fluid specimens examined several weeks apart revealed sheets of large atypical lymphoid cells positive for CD20, Pax-5, CD79a, CD45, MUM1, BCL2, BCL6 (weak) and negative for TTF1, CD68, MOC31, BER EP4, WT1, Calretinin, CD3, CD138, CD30, and cMYC. Human Herpesvirus-8 and Epstein-Barr virus were negative. Staging showed a few mildly fluorodeoxyglucose-avid mediastinal lymph nodes which were benign. Ultimately, the patient was diagnosed with fluid overload-associated large B-cell lymphoma and treated with rituximab, cyclophosphamide, vincristine sulfate, and prednisone, but passed away three months after diagnosis. <b>Conclusions</b>: Fluid overload-associated large B-cell lymphoma is a new and important diagnostic consideration in effusion-based lymphomas. It may be mistaken for other conditions such as primary effusion lymphoma or other diffuse large B-cell lymphomas. The presence of a Human Herpesvirus-8-negative effusion-based lymphoma in an elderly immunocompetent patient without nodal or tissue involvement should prompt consideration of fluid overload-associated large B-cell lymphoma.