This case report describes the diagnostic and therapeutic management of a 67-year-old female with a 40-year history of Sjögren disease (SjD) who was hospitalized for evaluation of recurrent fever lasting over one month. The patient' s initial diagnosis of SjD was established four decades earlier based on clinical manifestations, serological findings, and evidence of glandular damage. Her clinical presentation included recurrent parotid gland enlargement accompanied by sicca symptoms, notably persistent xerostomia and xerophthalmia, followed by progressive dental caries. Serological studies demonstrated positivity for antinuclear antibodies, anti-SSA/Ro, and anti-α-fodrin antibodies. Objective assessments confirmed significant ocular involvement (Schirmer' s test ≤5 mm/5 min) and pulmonary interstitial changes on chest CT, consistent with the 2016 American College of Rheumatology and European League Against Rheumatism (ACR/EULAR) classification criteria for SjD. The patient' s condition remained stable under low-dose corticosteroids and disease-modifying anti-rheumatic drugs (DMARDs) until the recent onset of prolonged fever, necessitating evaluation for fever of unknown origin. Differential diagnoses considered disease flare, infection, and malignancy. The European Sjögren' s Syndrome Disease Activity Index (ESSDAI) score was 5 points, indicating moderate systemic disease activity. Initial laboratory investigations revealed no evidence of infection, and empirical anti-infective therapy proved ineffective. Notably, despite the absence of lymphadenopathy, laboratory findings including borderline positive IgM λ M-protein, elevated lactate dehydrogenase, hyperferritinemia, and increased β2-microglobulin levels raised suspicion for lymphoproliferative disorders, given the established association between SjD and lymphoma. Bone marrow aspiration showed no significant abnormalities, but PET/CT imaging detected hypermetabolic lesions in the left breast and right distal femur, suggesting potential malignancy. Subsequent histopathological examination of the breast lesion confirmed non-Hodgkin' s lymphoma (NHL), specifically diffuse large B-cell lymphoma (DLBCL) of the germinal center B-cell (GCB) subtype. Treatment with R-CHOP chemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) induced complete metabolic remission after three cycles. However, she subsequently developed treatment-related complications, including myelosuppression and pulmonary infection. This case underscores the importance of maintaining a high index of suspicion for atypical site involvement in SjD patients, particularly when lymphoma risk factors are present. Comprehensive differential diagnosis should include lymphoma and other malignancies, and the diagnostic value of PET/CT and histopathological examination in disease evaluation is emphasized. SjD complicated by breast lymphoma is exceptionally rare, and its pathogenesis may involve lymphocytic infiltration, abnormal activation of lymphocytes, formation of ectopic germinal centers in the breast, and eventual malignant transformation. These mechanisms require further investigation through clinical and basic research studies.

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作者贡献说明  宁圆：收集、整理数据，撰写论文；张晓盈、李雪：分析数据，参与论文修改；李原：收集整理数据；何菁、金月波：总体把关和审定论文。