How do you approach a patient with endoscopic ileitis without typical features of chronicity on histology, who has worsening abdominal pain and increased stool frequency despite a trial of budesonide?

I am not sure, but I will assume "without typical features of chronicity" means it is either normal or acute inflammation. Acute inflammation is either prep effect, exogenous hormones, or NSAIDs, but this is not Crohn's and would be treated as IBS. If normal, then for sure treat as IBS.