Proteinuria With Functionally Normal Kidneys: A Hidden Clue to the Diagnosis of Diffuse Large B-cell Lymphoma (DLBCL) With Secondary Glomerular Infiltration.

Diffuse large B-cell lymphoma (DLBCL) is an aggressive, rapidly progressive type of non-Hodgkin lymphoma that arises from mature B lymphocytes and is characterized by diffuse involvement of lymph nodes as well as possible extranodal tissues. It typically presents with fever, night sweats, weight loss and lymph node enlargement. While extranodal organ involvement is relatively common, the renal involvement remains a rare and under-recognized manifestation. We report the case of a 66-year-old female patient initially admitted with lower respiratory tract infection (LRTI), who was later diagnosed with DLBCL involving the kidneys. The fever began a week before admission, and despite receiving appropriate treatment for LRTI, she continued to spike intermittent fevers. Clinical assessment revealed pedal oedema, hypoalbuminemia and nephrotic range proteinuria, with preserved renal function. A fluorodeoxyglucose positron emission tomography (FDG PET) scan demonstrated metabolically active cervical lymphadenopathy, and subsequent biopsies of kidney and cervical lymph node confirmed the diagnosis of DLBCL. Timely initiation of the polatuzumab vedotin, rituximab, cyclophosphamide, doxorubicin, and prednisolone (Pola-R-CHP) chemotherapy regimen led to significant clinical improvement within six weeks of diagnosis. This case highlights the importance of recognizing renal involvement in atypical presentations of DLBCL, emphasizing the need for clinical vigilance to facilitate early diagnosis, timely management, and improved patient outcomes.