A Rare Presentation of Lupus Nephritis: Postpartum Complement-Mediated Hemolytic Uremic Syndrome Mimicking Thrombotic Thrombocytopenic Purpura

Complement-mediated hemolytic uremic syndrome (CM-HUS) is a rare form of thrombotic microangiopathy (TMA) that may complicate systemic lupus erythematosus (SLE) and can be difficult to distinguish from thrombotic thrombocytopenic purpura (TTP), because both present with thrombocytopenia, microangiopathic hemolytic anemia, and end-organ injury. We report a 21-year-old woman with obesity, type 2 diabetes mellitus, nonalcoholic steatohepatitis, hypertriglyceridemia, and a positive antinuclear antibody who presented four months postpartum with nausea, vomiting, headache, and facial swelling. Evaluation revealed severe hypertension, anemia, thrombocytopenia, acute kidney injury, nephrotic-range proteinuria, and hematuria, and a peripheral smear showed schistocytes consistent with microangiopathic hemolytic anemia. Given concern for TTP, she underwent therapeutic plasma exchange and received high-dose corticosteroids with initial improvement. Further workup demonstrated markedly elevated anti-double-stranded DNA antibodies, profound hypocomplementemia, and biopsy-proven Class III lupus nephritis with thrombotic microangiopathy, while ADAMTS13 activity was preserved at 94%, effectively excluding TTP and supporting lupus-associated CM-HUS. Plasma exchange was discontinued and the patient was treated with hydroxychloroquine, mycophenolate mofetil, tacrolimus, and corticosteroids; complement inhibition with eculizumab was deferred given an ongoing response. At follow-up, platelet count and renal function normalized and hemoglobin stabilized on immunosuppression alone. Pregnancy and the postpartum period are recognized complement-amplifying states that may precipitate endothelial injury and unmask autoimmune disease. This case underscores that preserved ADAMTS13 activity, active lupus serologies, hypocomplementemia, and biopsy-proven lupus nephritis are critical to distinguishing CM-HUS from TTP and to guiding lupus-directed therapy that can achieve favorable hematologic and renal recovery.