Abstract Introduction Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy resulting from dysregulation of the alternative complement pathway, leading to uncontrolled complement activation and microvascular thrombosis. It is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. aHUS can be associated with various infectious and non-infectious triggers, including bacterial infections (most commonly Shiga toxin-producing Escherichia coli), pregnancy, and certain medications. Here, we present a rare case of a 50-year-old female with a history of well-controlled lupus who presented with Legionella pneumonia and was subsequently diagnosed with aHUS. Case Presentation A 50-year-old woman with SLE, hypertension, and CKD stage IIIb presented with three days of generalized weakness, poor intake, and altered mentation without diarrhea or vomiting. On presentation she was febrile with temperature 103 °F, tachycardic, and significantly hypertensive with blood pressure 220s/100s mmHg. She appeared lethargic with diffuse weakness, coarse crackles over both lung bases, and mild abdominal tenderness. She was admitted to the ICU and started empirically on vancomycin, cefepime, and metronidazole. Infectious workup revealed a positive Legionella urine antigen, negative blood and urine cultures, and unremarkable cerebrospinal fluid analysis. Peripheral smear showed schistocytes, and laboratory evaluation demonstrated evidence of hemolysis and acute kidney injury. Renal biopsy revealed thrombotic microangiopathy without features of lupus nephritis. ADAMTS13 activity was normal, excluding thrombotic thrombocytopenic purpura. There was no clinical or serologic evidence of antiphospholipid syndrome, and complement levels were depressed. These findings supported a diagnosis of complement-mediated TMA consistent with atypical HUS triggered by Legionella infection. Antibiotics were de-escalated to azithromycin once Legionella was confirmed. The patient received pulse-dose corticosteroids, daily plasmapheresis targeting a platelet count 150 K/µL, and intermittent hemodialysis for renal failure. Platelet counts improved, and she was eventually weaned off supplemental oxygen. At discharge, she remained dialysis-dependent but later recovered sufficient renal function to discontinue dialysis. She continues outpatient hematology follow-up for consideration of eculizumab therapy to prevent recurrence. Discussion Infection-associated aHUS represents uncontrolled complement activation in genetically or immunologically predisposed hosts. Legionella is a rarely reported trigger, with only a few cases documented. Early recognition of hemolysis, thrombocytopenia, and renal failure in the context of infection should prompt evaluation for TMA. Management centers on supportive care, prompt treatment of the underlying infection, and consideration of complement blockade with eculizumab to prevent irreversible renal injury and recurrence. This abstract is funded by: None
Leitch-Casey et al. (Fri,) studied this question.