Primary splenic diffuse large B-cell lymphoma masquerading as systemic lupus erythematosus: a case report.

Background: Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma, whereas primary splenic DLBCL (PS-DLBCL) is exceedingly rare. Lymphomas that mimic systemic lupus erythematosus (SLE) are clinically heterogeneous and share overlapping manifestations with SLE, rendering diagnosis extremely challenging. Case presentation: We report a case of an elderly patient presenting with recurrent fever, a hyperinflammatory state, and cytopenias, along with positivity for multiple autoimmune antibodies and lupus anticoagulant, which strongly suggested a clinical diagnosis of SLE. However, the patient showed no response to adequate doses of glucocorticoid therapy. Subsequent bone marrow and peripheral blood flow cytometry revealed a minor population of aberrant phenotype B cells, and positron emission tomography-computed tomography demonstrated mild splenomegaly with diffuse increased fluorodeoxyglucose uptake in the splenic parenchyma. A definitive diagnosis of PS-DLBCL was established following splenectomy. Unfortunately, the patient suffered sudden cardiac death shortly after diagnosis. Conclusion: This case highlights that PS-DLBCL can present with lupus-like manifestations as an atypical clinical feature, and such variant presentation may herald a poor prognosis.