B-cell lymphoma initially presenting as isolated pleural effusion: a challenging diagnostic case report.

Background: B-cell lymphoma is a highly heterogeneous group of diseases with complex clinical manifestations. While lymphoma-associated pleural effusion occurs in approximately 20-30% of cases, lymphoma presenting initially with pleural effusion as the primary manifestation is relatively uncommon. This case report demonstrates a rare presentation where massive pleural effusion was the primary clinical manifestation in the absence of typical lymphoma symptoms, leading to potential misdiagnosis and delayed treatment. The unique contribution to existing literature lies in highlighting the diagnostic pitfalls and providing a systematic approach for clinicians to recognize occult lymphoma in patients presenting with unexplained pleural effusion. Case Description: This article reports the case of a 76-year-old female patient who presented with chest tightness and pleural effusion lasting for 3 months. Cytomorphological examination of the pleural effusion identified lymphoma cells, leading to a diagnosis of B-cell lymphoma. Flow cytometry immunophenotyping of the pleural fluid and whole-body positron emission tomography-computed tomography (PET-CT) confirmed B-cell lymphoma, which is considered a B-cell lymphoma, with pleural effusion as the initial and predominant manifestation. Conclusions: We discussed the pathogenesis of B-cell lymphoma involving pleural effusion, and showed that cytomorphological examination of pleural effusion is a rapid and convenient method for promptly differentiating between benign and malignant effusions, providing important diagnostic information for initial screening, and helping avoid missed diagnoses.