A Rare Case of Atypical Hemolytic Uremic Syndrome Presenting as Chronic Interstitial Nephritis.

Atypical hemolytic uremic syndrome commonly presents as rapidly progressive renal failure and is histologically characterized by thrombotic microangiopathy (TMA). TMA presenting with acute renal failure requires aggressive medical management. Here, we present a case of a 30-year-old man who presented with a history of accelerated hypertension and a strong family history of end-stage renal disease, in September 2023. Upon evaluation, he was found to have a creatinine level of 2 mg/dl, bland urine and normal-sized kidneys; a renal biopsy revealed chronic interstitial nephritis. Genetic analysis for autosomal dominant tubulointerstitial kidney disease and nephronophthisis yielded negative results. The patient was managed with antihypertensive medications. In January 2024, he was admitted with a history of confusion, headache, and alcohol binge. He had a blood pressure of 200/100 mmHg and had grade 3 hypertensive retinopathy. Laboratory tests revealed anemia with thrombocytopenia, bland urine, normal coagulation parameters, indirect hyperbilirubinemia, normal-sized kidneys on ultrasound, and elevated lactate dehydrogenase levels. MRI of the brain revealed symmetrical hyperintensities in bilateral cerebellum and the dorsal brainstem. Complement levels revealed low C3 levels and genetic analysis revealed a homozygous deletion in the complement factor H-related 3 (CFHR3) gene. The autoantibody for complement factor H was negative. The patient was managed conservatively with adequate blood pressure control. This case highlights the effects of complement dysregulation on the renal tubulointerstitium.