Atypical haemolytic uremic syndrome (aHUS) and membranoproliferative glomerulonephritis (MPGN), different diseases or a spectrum of complement-mediated glomerular diseases?

Historically, patients with kidney diseases caused by genetic or acquired dysregulation of the complement alternative pathway have been grouped into clinical syndromes, C3 glomerulopathy (C3GN/DDD) and thrombotic microangiopathy (TMA), specifically atypical haemolytic uremic syndrome (aHUS). Recent data suggested that these diseases share a common pathophysiology and that patients can transition between glomerulopathies in this spectrum. Histopathologically, the main difference cited is the immunofluorescence (IF) findings, with C3 predominance in C3 glomerulopathy (compared with immunoglobulins and complements in immune complex-mediated membranoproliferative glomerulonephritis (MPGN)) and negative IF in TMA. We report a case in which a patient presented with hypertension, seizures, proteinuria, renal impairment and immune complex-mediated MPGN on kidney biopsy. Months later, she presented with classical TMA. She failed to respond to steroids and plasma exchange therapy but subsequently made a remarkable haematological and renal recovery after eculizumab treatment, thus supporting an underlying complement dysregulation and a diagnosis of aHUS.