ABSTRACT
Introduction: Atypical hemolytic uremic syndrome (aHUS) is a form of thrombotic microangiopathy (TMA) characterized by dysregulated complement activation. Antibodies to factor H (anti-FH), a regulator of the alternative complement pathway, are a recognized cause of aHUS particularly in children. We present the case of an elderly patient who developed aHUS following COVID-19. Case Description: A 74-year-old male presented with weakness, petechial rash involving extremities and diarrhea for 2 weeks. Prior history included hepatitis C infection status-post treatment 2 years ago with associated cirrhosis. Three weeks ago, the patient had been diagnosed with COVID-19. His symptoms of sore throat, cough and fever had by now resolved. Initial investigations showed leukocytosis and AKI with an active urinary sediment and nephrotic range proteinuria (Fig 1). Hemoglobin and platelets were normal and a blood smear was negative for hemolysis. Imaging revealed small bowel enteritis suggestive of an infectious or vasculitic process. Infectious workup returned negative. Autoimmune serologies revealed a borderline positive ANA, low C3 and low-normal C4. Renal biopsy revealed diffuse endothelial injury with swollen endothelial cells, focal mesangiolysis and glomerular basement membrane duplication. Hence, pulse dose steroids were started and complement function panel sent. Soon after steroid initiation, the patient's renal function, leukocytosis and rash improved. Ultimately, complement testing returned positive for anti-FH. At follow-up, renal function had returned to baseline with continued steroid taper. Discussion(s): COVID-19 is associated with TMA likely due to endothelial toxicity or complement pathway dysregulation. Our patient had no prior history of renal or hematologic disease. Given the chronology of events, it is likely that COVID-19 triggered formation of anti-FH, in turn leading to development of aHUS in our patient.