Refractory Lupus Nephritis Presenting with Myeloperoxidase (MPO)-ANCA-Positive, Rapidly Progressive Glomerulonephritis: A Case Report

Introduction: Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and systemic lupus erythematosus (SLE) are both autoimmune disorders that can present with rapidly progressive glomerulonephritis (RPGN). While clinical criteria and serological markers are used to classify these conditions, discrepancies can arise, as autoantibody profiles do not always correspond with disease activity or organ involvement. We present a case of steroid-resistant MPO-ANCA-positive lupus nephritis (LN), initially negative for anti-dsDNA antibodies. Case Description: A 61-year-old male was referred to our department with progressive systemic edema. He had no previous history of renal impairment. On admission, laboratory results showed hypoalbuminemia (1.9 g/dL) and elevated serum creatinine (2.56 mg/dL). Urinalysis revealed hematuria (>100 RBC/HPF), proteinuria (urine protein-to-creatinine ratio (UPCR) 9.5 g/gCr), and various urinary casts, consistent with nephrotic syndrome and RPGN. Immunological tests revealed an ANA titer of 1:40, anti-dsDNA 6 U/L, hypocomplementemia (C3 45 mg/dL, C4 5 mg/dL), and elevated MPO-ANCA (30 U/mL). Renal biopsy revealed fibrous crescents in all glomeruli without evidence of vasculitis on light microscopy. Immunofluorescence showed a full-house pattern, and electron microscopy demonstrated disrupted glomerular tufts with dense deposits. The patient was diagnosed with ISN/RPS class IV LN. The modified NIH activity and chronicity scores were 9/24 and 6/12, respectively. He received two courses of intravenous methylprednisolone (500 mg/day for three days), followed by daily intravenous prednisolone (80 mg). Despite high-dose steroid therapy, his renal function worsened, requiring hemodialysis (HD) on day 38. Rituximab (500 mg, weekly, four courses) was then administered, resulting in gradual clinical improvement. On day 110, he was able to discontinue HD. Maintenance therapy with azathioprine (100 mg/day) was initiated, allowing a tapering of prednisolone to 5 mg/day. Discussion: This case illustrates successful treatment of steroid-resistant lupus nephritis using rituximab. Patients with ANCA-positive lupus nephritis are more likely to experience severe and refractory renal disease, and rituximab may provide a valuable therapeutic alternative in such cases.