Treatment of exostosin 1-associated membranous lupus nephritis with multiple low doses of rituximab: A case report.

RATIONALE Membranous glomerulonephritis (MN) is the leading cause of nephrotic syndrome in adults and is classified as primary or secondary. Secondary MN accounts for 20% to 30% of all MN cases and can arise from a number of conditions, including autoimmune diseases. Recently exostosin 1/exostosin 2 (EXT1/EXT2) have been identified as the common antigens in secondary autoimmune MN and are present in cases of pure membranous lupus nephritis (LN). The treatment of EXT1/EXT2-associated MN remains elusive. PATIENT CONCERNS We present the case of a 15-year-old female who presented with nephrotic syndrome, positive ANA and dsDNA, and low serum complements. A renal biopsy revealed pure membranous nephritis with IgG and C3 deposition. EXT1 was found along the glomerular capillary walls and stained positive, while phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) were negative. DIAGNOSIS The patient was diagnosed with ETX1-associated membranous LN. INTERVENTIONS She was treated with prednisone and multiple low-dose rituximab (4 200 mg doses, approximately every 2 months, based on CD19+ cells counts). OUTCOMES The patient had complete remission within 8 months later, and she remained in remission for the 16-month period of follow-up. LESSONS To our knowledge, this is the first case of EXT1-associated MN that has been successfully treated by multiple low-dose rituximab. Further studies can investigate the optimal dosage and treatment protocol.