Kolitis Ulserativa

01Pathophysiology

Ulcerative colitis (UC) is a chronic inflammatory bowel disease in which a dysregulated immune response targets the colonic mucosa. The fundamental abnormality involves a breakdown of the intestinal epithelial barrier, which allows luminal antigens and commensal bacteria to penetrate the mucosa and trigger an inappropriate immune cascade. In genetically predisposed individuals (over 200 susceptibility loci have been identified, including HLA-DR2), environmental triggers such as enteric infections, dietary changes, or NSAID exposure initiate the inflammatory process.

The immune response in UC is driven predominantly by an atypical Th2 pathway characterized by elevated IL-5 and IL-13, which distinguishes it from Crohn's disease, where the response is Th1/Th17-mediated. IL-13 is directly cytotoxic to epithelial cells and impairs barrier function by disrupting tight junctions. This promotes further antigen translocation, creating a self-perpetuating cycle of inflammation. Neutrophils infiltrate the colonic crypts and form crypt abscesses, which are a hallmark histological finding. The chronic inflammation leads to goblet cell depletion, which reduces the protective mucus layer and further exposes the epithelium.

The inflammation in UC is confined to the mucosa and submucosa and does not penetrate the muscularis propria or serosa under normal circumstances. This is the key architectural distinction from Crohn's disease. Because the deeper layers are spared, fistulas, strictures, and sinus tracts do not develop in UC. The inflammation also follows a continuous, circumferential pattern beginning at the rectum and extending proximally without skip areas. This predictable distribution explains why the rectum is always involved and why a normal rectal biopsy essentially rules out UC.

This mucosal-only, continuous pattern directly explains the clinical features. Mucosal ulceration exposes submucosal blood vessels, producing bloody diarrhea. Rectal inflammation causes persistent urgency and tenesmus because the inflamed rectum cannot properly distend or store stool. Chronic blood loss leads to iron deficiency anemia. Over years, the chronic inflammatory insult causes mucosal atrophy and loss of the normal haustra, producing the classic "lead pipe" appearance on imaging. Islands of regenerating mucosa surrounded by ulcerated areas create pseudopolyps (inflammatory polyps), which are not premalignant themselves but indicate prior severe inflammation.

The one critical exception to the "mucosal-only" rule is toxic megacolon, in which inflammation extends transmurally, causing paralysis of the colonic smooth muscle, loss of tone, and dilation of the colon to greater than 6 cm. This is a life-threatening surgical emergency. Additionally, in patients with extensive pancolitis, inflammatory mediators may cause mild terminal ileum inflammation known as backwash ileitis, which can mimic Crohn's disease on imaging.

The chronic inflammation in UC follows a dysplasia-to-carcinoma sequence rather than the adenoma-to-carcinoma sequence seen in sporadic colorectal cancer. The cumulative risk of colorectal cancer increases with disease duration and extent, which is why surveillance colonoscopy is mandatory.

02Classification and Clinical Manifestation

Montreal Classification by Extent

Severity Grading (Modified Truelove and Witts Criteria)

Extraintestinal Manifestations

03Diagnostic Workup

The first step in any patient presenting with chronic or recurrent bloody diarrhea is to exclude infectious etiologies. Stool cultures, ova and parasite examination, and Clostridioides difficile toxin assay must be sent before any IBD-directed workup begins. This is a commonly tested principle: you cannot diagnose UC until infection is ruled out. In the acute setting, C. difficile is particularly important because it can cause a flare in a patient with established UC and requires targeted antibiotic treatment (vancomycin PO or fidaxomicin).

Baseline laboratory studies serve to grade disease severity. Iron deficiency anemia (microcytic, low ferritin) reflects chronic blood loss. Elevated ESR and CRP indicate systemic inflammation, and hypoalbuminemia signals severe disease with protein-losing enteropathy. Fecal calprotectin is a non-invasive stool marker released by neutrophils in inflamed mucosa. It is highly useful for distinguishing inflammatory bowel disease from irritable bowel syndrome, where calprotectin remains normal. It is also valuable for monitoring disease activity and predicting relapse without repeat colonoscopy.

Serologic markers help differentiate UC from Crohn's disease when colonoscopic findings are ambiguous. p-ANCA is positive in roughly 65% of UC patients and negative in most Crohn's patients. Conversely, ASCA (anti-Saccharomyces cerevisiae antibodies) is positive in 60 to 70% of Crohn's patients. These markers are supportive, not diagnostic, and should never replace tissue biopsy.

Colonoscopy with biopsy is the most accurate test and the gold standard for diagnosing UC. On endoscopy, the hallmark is continuous, circumferential inflammation beginning at the rectum and extending proximally without skip areas. The mucosa appears erythematous, edematous, and friable (bleeds on contact), with loss of the normal vascular pattern. In more advanced disease, shallow ulcers, pseudopolyps, and spontaneous bleeding are seen. The transition between inflamed and normal mucosa is sharply demarcated. Biopsies show crypt abscesses (neutrophils within crypt lumens), crypt architectural distortion (branching, shortening), and goblet cell depletion. Importantly, the inflammation is limited to the mucosa and submucosa, and granulomas are absent (granulomas point toward Crohn's disease).

In acutely ill patients with suspected toxic megacolon, colonoscopy and barium enema are absolutely contraindicated due to the risk of perforation. Instead, a plain abdominal X-ray is the appropriate initial imaging study, which will show dilation of the transverse colon greater than 6 cm with loss of haustra and possible thumbprinting from edematous bowel wall.

04Management and Treatment

Induction of Remission

For mild to moderate disease, the cornerstone of therapy is 5-aminosalicylic acid (5-ASA), with mesalamine being the preferred formulation. Combined oral and rectal mesalamine (topical plus systemic) is more effective than either route alone and should be the standard approach. Oral mesalamine is dosed at 2.4 to 4.8 g/day in divided doses. For isolated proctitis, a mesalamine rectal suppository at 1 g nightly is often sufficient. For left-sided disease, a mesalamine retention enema at 4 g nightly is added to oral therapy.

Sulfasalazine (4 to 6 g/day in divided doses for induction, 2 to 4 g/day for maintenance) is an older 5-ASA agent that remains effective but carries more side effects: headache, nausea, rash, reversible oligospermia, and folate malabsorption. Patients on sulfasalazine should receive folic acid supplementation at 1 mg/day.

If 5-ASA agents fail, the next step is oral corticosteroids. Prednisone is started at 40 to 60 mg/day and tapered by 5 to 10 mg per week over approximately 8 to 12 weeks. Budesonide MMX at 9 mg/day is an alternative with fewer systemic side effects for mild to moderate disease. The essential principle for exam purposes: corticosteroids are for induction of remission only and must never be used as maintenance therapy due to cumulative toxicity (osteoporosis, adrenal suppression, hyperglycemia, cataracts, avascular necrosis).

For moderate to severe disease not responding to steroids, or for patients who are steroid-dependent (relapse upon tapering), escalation to immunomodulators or biologic therapy is required. Azathioprine (2 to 2.5 mg/kg/day) or its metabolite 6-mercaptopurine (1 to 1.5 mg/kg/day) are used as steroid-sparing agents. Before initiating either drug, TPMT (thiopurine methyltransferase) enzyme activity must be checked: patients with low or absent TPMT activity are at high risk of severe myelosuppression. The onset of action is 3 to 6 months, so these agents cannot be relied upon for acute flares.

Biologic agents are indicated for moderate to severe disease refractory to conventional therapy:

Before starting any anti-TNF agent, screen for latent tuberculosis (PPD or interferon-gamma release assay) and hepatitis B (HBsAg, anti-HBc), because TNF-alpha blockade can reactivate both infections.

Severe and Fulminant Disease

Patients requiring hospitalization receive IV corticosteroids (methylprednisolone 60 mg/day or hydrocortisone 100 mg IV every 8 hours). They should be evaluated daily with stool frequency counts, vital signs, and serial abdominal exams. If there is no meaningful improvement within 3 to 5 days, the patient has steroid-refractory disease and requires rescue therapy with either IV cyclosporine (2 to 4 mg/kg/day continuous infusion) or infliximab (5 mg/kg IV). The choice between these depends on institutional expertise; both have comparable short-term efficacy.

For toxic megacolon, immediate supportive measures include NPO status, nasogastric tube decompression, IV fluid resuscitation, broad-spectrum IV antibiotics (covering gram-negative and anaerobic organisms), and IV corticosteroids. Anticholinergics, opioids, and antidiarrheals must be discontinued because they reduce colonic motility and worsen dilation. A surgical consult should be obtained at admission. If the patient does not improve within 24 to 72 hours, or if perforation, peritonitis, or uncontrolled hemorrhage develops, emergent total colectomy is indicated.

Surgical Management

Total proctocolectomy with ileal pouch-anal anastomosis (IPAA) is the surgical procedure of choice and is curative in UC. This distinguishes it fundamentally from Crohn's disease, where surgery is palliative and recurrence is expected. Surgical indications include: refractory disease despite maximal medical therapy, steroid dependence unresponsive to biologics, toxic megacolon not responding to medical management, perforation, uncontrolled hemorrhage, and high-grade dysplasia or confirmed colorectal carcinoma.

A known complication of IPAA is pouchitis, an inflammation of the ileal pouch that presents with increased stool frequency, urgency, bleeding, and cramping. It is treated with a course of metronidazole or ciprofloxacin.

Cancer Surveillance

Patients with UC have an increased risk of colorectal cancer that rises with disease duration and extent. Surveillance colonoscopy with random biopsies every 1 to 2 centimeters should begin 8 to 10 years after diagnosis for pancolitis and 15 years after diagnosis for left-sided disease, then repeated every 1 to 2 years. Patients with concurrent primary sclerosing cholangitis require annual surveillance colonoscopy starting at the time of PSC diagnosis, regardless of UC duration, because PSC independently increases colorectal cancer risk.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on UC questions is by confusing it with Crohn's disease when the vignette includes a detail designed to create ambiguity. The distinguishing features to anchor on are: UC inflammation is continuous from the rectum, involves mucosa and submucosa only, produces no granulomas on biopsy, and does not cause fistulas, strictures, or perianal disease. If the vignette mentions skip lesions, terminal ileum involvement, transmural inflammation, granulomas, or fistulas, the answer is Crohn's, regardless of the other features presented.

A second high-frequency trap involves the concept of backwash ileitis. In pancolitis, mild inflammation of the distal terminal ileum can occur and may suggest Crohn's on imaging. However, true backwash ileitis is superficial, limited to a short segment, and always occurs in the context of extensive colitis extending to the cecum. If the vignette describes terminal ileum involvement with cobblestoning, deep ulcers, or skip areas, that is Crohn's.

Students frequently forget that smoking is protective in UC but harmful in Crohn's disease. A vignette featuring a non-smoker with bloody diarrhea and continuous colonic inflammation is reinforcing the UC diagnosis. The reverse pattern (smoker with skip lesions and ileal disease) points to Crohn's.

Another common error is selecting corticosteroids for maintenance therapy. Steroids are for induction only. The "next best step" after inducing remission with prednisone is always to transition to a steroid-sparing agent (mesalamine for mild disease, azathioprine/6-MP or biologics for moderate to severe disease). Any answer choice offering long-term prednisone is a distractor.

When a vignette describes a UC patient with suddenly worsening bloody diarrhea after antibiotic exposure, the next best step is to test for C. difficile before escalating IBD therapy. Superinfection is common and treatable, and missing it is a tested pitfall.

For toxic megacolon, the trap is ordering colonoscopy or barium enema. Both are absolutely contraindicated because they increase the risk of perforation. The correct initial study is a plain abdominal radiograph, and the correct management is medical stabilization followed by colectomy if no improvement occurs within 24 to 72 hours.

Finally, students should remember that the extraintestinal manifestation most associated with UC on exams is primary sclerosing cholangitis (PSC). PSC does not correlate with colonic disease activity, does not resolve after colectomy, and independently raises the risk of both cholangiocarcinoma and colorectal cancer. Any UC patient diagnosed with PSC requires annual surveillance colonoscopy from the time of PSC diagnosis, irrespective of UC duration or extent.

The core competency tested across UC questions is the ability to distinguish it from Crohn's disease using pattern recognition (continuous vs. skip, mucosal vs. transmural, rectum always involved vs. rectum often spared), to sequence the diagnostic workup correctly (exclude infection first, then colonoscopy with biopsy), and to apply the correct treatment escalation ladder without falling into the steroids-as-maintenance trap.