S4903 Atypical Hemolytic Uremic Syndrome in a Patient With Crohn’s Disease

Introduction: Atypical hemolytic uremic syndrome (aHUS) is a life-threatening thrombotic microangiopathy (TMA) due to complement dysregulation. While commonly associated with genetic or acquired complement abnormalities, inflammatory triggers such as infections, autoimmune, conditions, and malignancies are recognized precipitants. We present a case of aHUS occurring in a patient recently diagnosed with Crohn’s disease. Case Description/Methods: A 34-year-old man diagnosed with inflammatory colonic Crohn's disease 4 months prior, being treated with prednisone 40 mg and mesalamine 2.4 g daily, awaiting to start biologic treatment, presented with 5 days of melena and fatigue. Labs showed hemoglobin 5.4 g/dL, platelets 53 K/mm3, creatinine 9.5 mg/dL, LDH 2,244 U/L, haptoglobin <6 mg/dL. Blood smear revealed occasional schistocytes. Stool culture was negative for Shiga toxin-producing E. coli. Due to concern for thrombotic thrombocytopenic purpura, the patient was treated with 5 plasma exchanges. When ADAMTS13 activity level returned at 71% and complement proteins C3 and C4 were low at 84 and 8 mg/dL, respectively, the patient was diagnosed with aHUS. The patient was vaccinated for encapsulated organisms and started on eculizumab with improvement in his anemia, thrombocytopenia, and oliguric acute kidney injury. The patient was found to be Factor H autoantibody positive and genetic analysis showed a homozygous deletion of CFHR3-CFHR1 (associated with an increased risk of developing Factor H autoantibodies, which raise the risk of developing aHUS). Ten months later, the patient was evaluated for persistently elevated liver function tests and diagnosed with PSC based on suggestive findings on MRCP. Discussion: aHUS is a serious complication of complement dysregulation that may be triggered by systemic inflammatory states. A limited number of case reports have associated IBD with aHUS. Given the absence of infectious pathogens on extensive work-up, our patient's aHUS was suspected to be triggered by his underlying IBD. Crohn’s disease likely served as the inflammatory “second hit” in a genetically predisposed patient, leading to complement mediated-TMA. The initial presentation of fatigue, melena, anemia, thrombocytopenia, and acute kidney injury is not uncommon in IBD flares, which can delay recognition of coexisting TMA. Providers should maintain a high index of suspicion for uncommon but grave extraintestinal manifestations of IBD and consider early complement testing if TMA is suspected.