A 55-year-old man has a 4-month history of frequent and urgent defecation with loose and bloody stool, mild abdominal cramping, and fatigue. He does not have fever, nausea, or vomiting, but he has lost 3kg.he has mild joint pain in his knees and ankles for 4 months, is worse in the morning, and resolves somewhat during the day. on examination there is mild lower abdominal tenderness without rebound or guarding. Rectal exam shows gross blood, laboratory studies reveal a hemoglobin level 12.3 g/dL, MCV: 76fl. colonoscopy shows continuous erythema, friability, and loss of vascular pattern from the rectum to the splenic flexure. The rest of the colon and terminal ileum is normal, Histology shows cryptitis, crypt abscesses, and crypt architecture distortion. Which of the following is the most likely diagnosis?