A simple IBD flare?

33 year old male with ulcerative colitis presents with a 5-day history of fever, night sweats, abdominal pain and increased stool frequency. Medications include mesalazine M/R 1g once daily, 6-mercaptopurine 75mg once daily and a two week course of prednisolone 40mg once daily. Bloods revealed a leukopenia and c-reactive protein of 23. Based on the flexible sigmoidoscopy (figure) findings what is the most likely diagnosis? How would this change your management?

Submitted by Matthew Armstrong, Tom Thomas, Tariq Iqbal, Ralph Boulton and Jason Goh .

Gastroenterology department, University Hospital Birmingham, Birmingham, UK.