Abstract
Atypical/complement-mediated hemolytic uremic syndrome (A-HUS/CM-HUS) is a hereditary or sporadic disease with thrombotic microangiopathy (TMA). Diarrhea is a trigger that can cause attacks of CM-HUS. Although there are opinions that complement system activation plays a role in intestinal inflammation in patients with inflammatory bowel disease, the association of TMA with inflammatory bowel disease (IBD) has rarely been reported. In our case, a CM-HUS case that developed without an additional triggering factor in the course of ulcerative colitis (UC) was successfully treated with eculizumab, and then UC remission was also achieved. In this context, we would like to point out that the irregularities in the alternative pathway of the complement system may cause clinical findings in extra-renal organs, and the complement system may also play a role in the pathogenesis of inflammatory bowel disease. In addition, we think that our case may guide further studies on the usability of anti-complement therapies in treating patients with IBD who are resistant to conventional treatments.