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Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. In 2013, we developed diagnostic criteria to enable early diagnosis and timely initiation of appropriate treatment for aHUS. Recent clinical and molecular findings have resulted in several proposed classifications and definitions of thrombotic microangiopathy and aHUS. Based on recent advances in this field and the emerging international consensus to exclude secondary TMAs from the definition of aHUS, we have redefined aHUS and proposed diagnostic algorithms, differential diagnosis, and therapeutic strategies for aHUS. [ABSTRACT FROM AUTHOR]

We report a case of atypical hemolytic uremic syndrome ( aHUS) in a 4-year-old boy. Although the patient had the typical triad of aHUS (microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury), urgent dialysis was not indicated because he had neither oliguria nor severe electrolyte abnormality. He was given eculizumab as first-line therapy, which led to significant clinical improvement, thus avoiding any risk of complications associated with plasma exchange and central venous catheterization. Retrograde functional analysis of the patient's plasma using sheep erythrocytes indicated an increase in hemolysis, suggesting impairment of host cell protection by complement factor H. The use of eculizumab as first-line therapy in place of plasma exchange might be reasonable for pediatric patients with aHUS. [ABSTRACT FROM AUTHOR]

Background: Severe hypertension (HTN) and acute kidney injury frequently associated with atypical hemolytic uremic syndrome (aHUS) were refractory to various therapies in the pre-eculizumab era. Here we report the case of a 4-month-old boy who developed aHUS presenting with undetectable C3 protein, no predisposing mutations in complement factors, and no antibodies against factor H. Methods: Repeated plasma infusions and nine sessions of plasmapheresis were ineffective. The patient initially required continuous hemodiafiltration and thereafter peritoneal dialysis. Despite vigorous antihypertensive treatment and improved fluid overload with dialysis, HTN persisted. His low C3 level (<20 mg/dl) suggested unrestricted complement activation. Therefore, based on the suspicion of unrestricted complement cascade in the pathogenesis, treatment with eculizumab, a human anti-C5 monoclonal antibody, was initiated with the aim of controlling disease activity. Results: Eculizumab therapy resulted in the control of severe HTN and cessation of peritoneal dialysis. Conclusions: This infant with HTN and acute kidney injury associated with aHUS was treated successfully with eculizumab. [ABSTRACT FROM AUTHOR]

Atypical hemolytic uremic syndrome ( aHUS) is rare and comprises the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Recently, abnormalities in the mechanisms underlying complement regulation have been focused upon as causes of aHUS. The prognosis for patients who present with aHUS is very poor, with the first aHUS attack being associated with a mortality rate of approximately 25%, and with approximately 50% of cases resulting in end-stage renal disease requiring dialysis. If treatment is delayed, there is a high risk of this syndrome progressing to renal failure. Therefore, we have developed diagnostic criteria for aHUS to enable its early diagnosis and to facilitate the timely initiation of appropriate treatment. We hope these diagnostic criteria will be disseminated to as many clinicians as possible and that they will be used widely. [ABSTRACT FROM AUTHOR]