Describe the approach.
Evaluate patients with hematochezia and fecal urgency for ulcerative colitis.
Rule out infectious gastroenteritis.
Consult gastroenterology for ileocolonoscopy with histological examination
Consider CT or MRI abdomen if direct endoscopy is contraindicated.
Desribe lab studies.
Stool testing for causes of gastroenteritis is indicated in all patients. Blood tests are not routinely required for diagnosis but help assess disease activity and severity.
CBC: anemia, leukocytosis, thrombocytosis 
ESR, CRP: Elevated levels may indicate active ulcerative colitis and often correlates with disease severity.
ALP, GGT: elevated in patients with concurrent PSC
Perinuclear ANCA (pANCA) 
Not routinely recommended
Elevated in up to 70% of patients with ulcerative colitis
Stool diagnostic studies
Stool test for Clostridioides difficile infection
PCR panel for other enteric infections: depending on the patient's symptoms and risk factors for diarrhea
Stool culture and microscopy: to assess for bacteria and ova and parasites if a stool PCR panel is not available
Fecal calprotectin: can help assess for mucosal inflammation
Describe the ileocolonoscopy.
Recommended method for diagnosis and disease monitoring
Severe disease is a relative contraindication.
Describe the sigmoidoscopy amd EGD.
Initially used as an alternative to colonoscopy, e.g., in ASUC
Findings are similar to colonoscopy findings.
EGD: recommended for patients with upper gastrointestinal symptoms to rule out Crohn disease
What is the highest risk?
Patients with severe ulcerative colitis have a high risk for colonic perforation; therefore, caution should be used when performing biopsies.
Imaging studies are not routinely recommended for diagnosing ulcerative colitis but may be used as an adjunct to endoscopy, particularly for the detection of complications, or if endoscopy is not possible.
Describe abdominal x-rays.
Indication: initial and serial evaluation of suspected ASUC
Typically normal in mild-to-moderate disease
Loss of colonic haustra (lead pipe appearance) may be seen in severe cases
May show signs of complications, e.g.:
Toxic megacolon: massive distention
Ulceration: segmental dilation with irregular edges outlined by gas 
Describe CT/MRI abdomen.
Patients with abdominal symptoms that cannot be explained by the disease activity seen on endoscopy
To evaluate for:
Proximal disease involvement if endoscopy is not possible
Complications, e.g., bowel perforation
Differential diagnoses, e.g., Crohn disease
Loss of haustra
Increased bowel wall thickness
Signs of complications (similar to abdominal x-ray findings)
Describe Barium enema radiography.
The role of barium enema is limited, as it is less sensitive than other imaging modalities and is contraindicated in patients with obstruction or perforation.
Indication: can be considered for assessment of the proximal colon if colonoscopy is contraindicated
Granular appearance of the mucosa
Loss of haustra
Pseudopolyps that appear as filling defects
Describe abdominal ultrasound.
Indication: monitoring disease activity and treatment response
Findings: increased bowel wall thickness
List histological findings.
Granulocyte (neutrophil) infiltration: limited to mucosa and submucosa
Crypt abscesses: an infiltration of neutrophils into the lumen of intestinal crypts due to a breakdown of the crypt epithelium
Altered crypt architecture
Branching of crypts
Irregularities in size and shape
In ulcerative colitis, the extent of intestinal inflammation is limited to the mucosa and submucosa. In contrast, Crohn disease shows a transmural pattern of intestinal involvement.
Noncaseating granulomas are seen in Crohn disease but are not a feature of ulcerative colitis!
Crohn disease (see “Differential diagnostic considerations: Crohn disease and ulcerative colitis”)
C. difficile colitis
Escherichia coli colitis
Describe the microscopic colitis as a DD.
Definition: an idiopathic, inflammatory form of colitis that is characterized by a normal macroscopic appearance of bowel on colonoscopy and collagenous or lymphocytic infiltrates on microscopy
Forms: collagenous colitis and lymphocytic colitis
Peak incidence: ∼ 60 years of age
♀ > ♂
Chronic, nonbloody, watery diarrhea for > 4 weeks
Gross pathology: normal appearance
Collagenous colitis: proliferation of collagenous connective tissue that forms a thick, subepithelial collagen band
Lymphocytic colitis: mainly lymphocytic infiltrates with little/no proliferation of connective tissue
Cease nonsteroidal anti‑inflammatory drugs (NSAIDs may be a trigger for disease)
Symptomatic therapy (e.g., loperamide for mild diarrhea)