Case Report: A case of rituximab for membranous nephropathy secondary to primary Sjogren’s syndrome and literature review

Background: Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease characterized by lymphoplasmacytic infiltration of exocrine glands, leading to dry eyes and mouth. Renal involvement, particularly glomerulonephritis, occurs in approximately 5% of pSS patients. Membranous nephropathy (MN) is one of the less common forms of renal involvement in pSS. Case presentation: A 48-year-old female with a history of oral and ocular dryness for several years and bilateral symmetrical lower extremity edema for three months was admitted to our hospital. Laboratory findings revealed moderate anemia, hypoalbuminemia, and nephrotic-range proteinuria. Schirmer's test, tear break-up time, and lip biopsy confirmed the diagnosis of pSS. Renal biopsy demonstrated widespread mesangial hypercellularity and mesangial matrix expansion, thickening of the glomerular basement membrane(GBM) with prominent spikes, and subepithelial, intramembranous and mesangial electron-dense deposits under electron microscopy. Immunofluorescence showed diffuse fine granular deposits of IgG (predominantly IgG1 and IgG2). Based on these findings, secondary membranous nephropathy due to pSS was diagnosed. Treatment and outcome: The patient was treated with prednisone (30 mg/day) and two infusions of rituximab (1 g each, administered 2 weeks apart). After treatment, her 24-hour urinary protein level decreased from 8.5 g to 2.2 g. The dose of glucocorticoids was gradually tapered off. During follow-up, an additional 1 g of rituximab was administered six months later, resulting in a further reduction of proteinuria to 1.3 g/24 hours. Conclusion: This case highlights the effectiveness of rituximab in managing secondary membranous nephropathy associated with pSS. Further studies are needed to clarify the underlying mechanisms and optimize treatment strategies for this condition.