Atypical HUS and Crohn’s disease—interference of intestinal disease activity with complement-blocking treatment

Background In atypical hemolytic-uremic syndrome (aHUS), various defects of the complement system have been reported to explain pathophysiology. Therapeutic options for complement inhibition are well-recognized; however, the links between various immune-derived diseases and aHUS are unclear, and their interference with treatment efficacy during long-term complement-blocking therapy is scarcely known. Case-diagnosis/treatment We present a pediatric patient who developed aHUS with acute kidney injury in parallel with the onset of Crohn’s disease (CD), and who required long-term complement-blocking therapy with eculizumab (ECU). Unexpectedly, during the 6-year ECU treatment, an important intra-patient variation of the degree of complement inhibition was observed. In spite of continuous and stable doses of complement-blocking therapy, periods of incomplete blockade were observed in strong association with relapses of CD. When conventional and later biological therapy with adalimumab was introduced, with CD going into remission, complement blockade became complete again. Despite periodically low ECU levels and insufficient complement inhibition, no clinical or hematological signs of aHUS recurrence were detected during CD relapses. Conclusion In aHUS cases secondary to CD, close monitoring of both complement inhibition and serum ECU levels is needed as intestinal disease can interfere with complement-blocking treatment. Increased doses of ECU may be necessary to maintain therapeutic blood levels of ECU and full complement blockade, especially if the intestinal disease is not under control.