A 23-year-old woman presents with a 7-day history of abdominal pain, and now bloody diarrhea that brings her to her primary care physician. Review of systems is notable for a 12-pound unintentional weight loss and intermittent loose stools. She has a family history notable for a father with coronary artery disease and a mother with primary sclerosing cholangitis. Her temperature is 37.2°C (98.9°F), blood pressure is 100/72 mmHg, pulse is 72/min, respirations are 12/min, and oxygen saturation is 100% on room air. Her abdomen is soft, mildly diffusely tender to deep palpation, and non-distended. She is found to have the finding on colonoscopy in Figure A. Serum perinuclear antineutrophil cytoplasmic antibodies (p-ANCA) are positive. Which of the following is most likely to be present in this patient?
Continuous lesion beginning in the rectum
Fistulae and stricture formation
Worse disease severity near the ileocecal valve
Perianal disease
Continuous lesion beginning in the rectum
This patient presents with features suggestive of inflammatory bowel disease (IBD), and her colonoscopic and serologic studies suggest ulcerative colitis (UC). UC typically begins in the rectum and progresses proximally towards the ileocecal valve in a continuous fashion.

The diagnosis of IBD should always prompt further investigation to better delineate between UC, Crohn disease, or indeterminate colitis. Further delineation guides treatment and informs prognosis. UC has a peak incidence in the second and third decades of life. It is characterized by disease extending from the rectum proximally towards the ileocecal valve in a continuous fashion. UC presents as mucosal and submucosal inflammation, with characteristic crypt distortion and presence of crypt abscesses. P-ANCA is positive in most individuals with UC. Repeated mucosal injury can induce pseudopolyp formation, and pancolitis or disease in the descending colon warrants screening colonoscopy due to increased risk of colon cancer. On imaging, the colon can be dilated by edema, losing its haustral markings and giving it a "lead pipe" appearance.

Gajendran et al. review the pathophysiology, diagnosis, and treatment of UC. They found that colonoscopy with biopsy is the best way to make a definitive diagnosis of UC. They recommend the Mayo scoring system as a commonly used method of assessing disease severity, guiding treatment options, and monitoring patients during therapy.

Figure A is a colonoscopy image showing continuous colonic mucosal inflammation typical of ulcerative colitis.

Incorrect Answer:
Answer A: Cobblestoning and skip lesions refer to the patchy areas of inflammation noted in Crohn disease. In contrast, the inflammation seen in UC involves continuous stretches of colon mucosa.

Answer C: Fistulae and stricture formation are features of Crohn disease, not UC. Fistulizing and stricture formation can affect the entire gastrointestinal tract in Crohn disease.

Answer D: Perianal disease is a feature of Crohn disease. Although UC commonly affects the rectum, it tends to spare the anus.

Answer E: Worse disease severity near the ileocecal valve is a feature of Crohn disease and not UC. UC tends to be characterized by more uniform disease severity spanning in continuous fashion from rectum towards the cecum.

Bullet Summary:
Ulcerative colitis is characterized by disease extending from the rectum proximally towards the ileocecal valve in a continuous fashion.