Diagnostic Challenges in Atypical Hemolytic Uremic Syndrome: A Case of Artificial Mitral Valve Dysfunction as a Possible Trigger for Severe Thrombotic Microangiopathy

BACKGROUND Hemolytic uremic syndrome (HUS) is a severe disease classified under thrombotic microangiopathies and characterized by acute kidney injury, microangiopathic hemolytic anemia, and thrombocytopenia. HUS can be divided into 2 subtypes: typical HUS and atypical HUS (aHUS). The standard treatment for aHUS, a complement-mediated thrombotic microangiopathy, as approved in the United States and European Union involves long-term administration of eculizumab or ravulizumab with complement-mediated thrombotic microangiopathy. This report is of a 70-year-old woman with aHUS triggered by artificial mitral valve dysfunction. CASE REPORT A 70-year-old woman with history of artificial mitral valve replacement was admitted to the nephrology department with suspected HUS. She presented with malaise, dyspnea, anemia, thrombocytopenia, hemolysis, and schistocytes in blood smear. Complement factors were normal, but sC5b-9 was elevated, suggesting complement overactivation. ADAMTS-13 was >10%, ruling out thrombotic thrombocytopenic purpura. Infection with a Shiga toxin-producing bacterium was ruled out. Genetic tests for complement factors revealed no pathogenic variants. The patient was treated with eculizumab, leading to significant clinical improvement. Due to her cardiac history, a comprehensive cardiologic evaluation was performed, revealing perivalvular leakage and severe dysfunction of the mitral valve prosthesis. She subsequently underwent a 2-step intravascular mitral valve repair. The administration of eculizumab resulted in clear improvement in hemolysis, renal function, and platelet count prior to mitral valve surgery, strongly supporting the diagnosis of an aHUS-type thrombotic microangiopathy. Surgical intervention was subsequently performed and contributed to long-term stabilization. CONCLUSIONS This case underscores the challenges of treating thrombotic microangiopathy in a patient with multiple comorbidities and complicated medical history.