Proctitis vs Left-Sided Colitis vs Pancolitis: Why Extent Changes Symptoms + Treatment
Last Updated Jan 15, 2026
Ulcerative colitis (UC) is often described by its extent, meaning how far inflammation spreads through the large intestine (colon). Extent is different from severity (how inflamed the lining looks and how intense symptoms feel). Knowing the extent helps explain why two people with “UC” can have very different day-to-day symptoms, and why treatment plans may use rectal medicines, oral medicines, or both.
Understanding extent of UC (proctitis, left-sided colitis, pancolitis)
UC usually starts in the rectum and can extend upward in a continuous pattern. Many gastroenterology teams document extent using the Montreal classification: E1 proctitis (rectum only), E2 left-sided colitis (up to the bend near the spleen), and E3 extensive colitis, which includes pancolitis when most or all of the colon is involved. [1]
Symptoms can shift with location because different parts of the colon do different jobs (absorbing water, storing stool, and signaling the need to go). In ulcerative proctitis, symptoms often center on the rectum: rectal bleeding, urgency, rectal pain, and sometimes constipation. Left-sided colitis (left sided colitis meaning inflammation in the rectum plus the sigmoid and descending colon) is more likely to cause bloody diarrhea along with cramping or pain, often on the left side, plus a frequent feeling of needing to pass stool even when little comes out. Pancolitis symptoms can look similar but broader, with more frequent or severe diarrhea and a higher chance of whole-body effects like fatigue and weight loss when inflammation is more widespread. [2]
A quick mental shortcut: more colon involved can mean more diarrhea, while more rectum involved can mean more urgency and “false alarm” trips. Still, symptom intensity does not always perfectly match extent, which is one reason colonoscopy results matter.
Why extent changes symptoms and treatment (and why colonoscopy reports include scoring)
Extent is usually confirmed on colonoscopy, which shows where inflammation is and how active it looks. Many reports include an endoscopic activity score. One widely used scoring system is the Mayo endoscopic subscore, which rates inflammation from 0 to 3 based on what the lining looks like during the exam. [3]
Extent also helps explain why the route of medication delivery matters. Rectal meds for UC (like suppositories, enemas, or foams) are designed to deliver anti-inflammatory medicine directly to the rectum and lower colon, where proctitis and many cases of left-sided disease are located. Oral medicines travel through more of the digestive tract and can treat a larger stretch of colon. In mild to moderate disease, clinical guidelines commonly favor rectal mesalamine for proctitis, and often suggest adding rectal mesalamine to oral therapy for left-sided or extensive UC, because combining routes can better cover the inflamed areas. [4]
Another reason “extent” shows up repeatedly in care plans is that it can change over time. Some people diagnosed with proctitis or left-sided colitis later develop more proximal (upward) extension, which is one reason clinicians track symptoms, labs, and periodic colon evaluations when appropriate. [5]