A 30-yeаr-оld pаtient with а 5-year histоry оf Crohn’s disease is admitted with severe abdominal pain, diarrhea, and fever. The physician is considering a differential diagnosis of exacerbation versus a flare of ulcerative colitis, which the patient’s sibling was recently diagnosed with. Which of the following findings would most strongly differentiate Crohn’s disease from ulcerative colitis?