Complement-Amplifying Conditions in Atypical Hemolytic Uremic Syndrome: A Canadian Case Series

RATIONALE: Thrombotic microangiopathies (TMAs) are systemic disorders that often affect the kidneys and encompass a heterogeneous group of conditions, including atypical hemolytic uremic syndrome (aHUS). The complement pathway is thought to play a crucial role in the pathogenesis of aHUS, and a favorable response can be obtained through complement C5 inhibition. There is emerging evidence to suggest that the same is also true for several other forms of TMA. OBJECTIVE: The purpose of this series is to report cases of aHUS in which both an innate defect of the alternative complement pathway and a complement-amplifying condition were suspected. METHODS: This case series describes 8 patients who were managed in Canadian tertiary centers for aHUS and who presented initially with complement-amplifying conditions. RESULTS: In all cases, aHUS was associated with organ dysfunction and in some, with an innate defect of the alternative complement pathway. The complement-amplifying conditions identified were diverse including immune disorders, pregnancy, and a Shiga toxin infection. Patients improved rapidly when treated with eculizumab or plasma exchange. CONCLUSIONS: These observations illustrate the seriousness of secondary aHUS. They also add to existing lines of evidence that the complement pathway is potentially involved in this condition and that it should be considered as a therapeutic target of interest under such circumstances.