Intestinal & Colorectal Disorders

Intestinal & Colorectal Disorders: Inflammatory, Functional, and Screening Protocols

Inflammatory Bowel Disease (IBD): Crohn Disease vs. Ulcerative Colitis

Inflammatory bowel disease (IBD) is classified into Crohn disease (CD) and ulcerative colitis (UC). Distinguishing between them is a core Step 3 requirement because it dictates surgical and medical options:

• Anatomical Distribution: CD can affect any part of the gastrointestinal tract from the mouth to the anus, characteristically displaying "skip lesions" with rectal sparing. The terminal ileum is the most common site of involvement. UC is strictly limited to the colon and rectum, displaying continuous mucosal inflammation that starts in the rectum and extends proximally.
• Histopathology: CD is characterized by transmural inflammation, non-caseating granulomas, linear mucosal ulcers, and a cobblestone appearance. The transmural nature leads to complications like strictures, fistulas, and perianal disease (abscesses, fissures). UC is characterized by superficial inflammation restricted to the mucosa and submucosa, crypt abscesses, and pseudopolyps.
• Extraintestinal Manifestations: Both are associated with aphthous ulcers, uveitis, episcleritis, erythema nodosum, pyoderma gangrenosum, and arthritis. However, primary sclerosing cholangitis (PSC) is strongly associated with UC, while gallstones and nephrolithiasis (calcium oxalate stones due to increased oxalate absorption in the colon) are more common in CD.
• Therapeutics: Mild-to-moderate UC is managed with topical or oral 5-aminosalicylates (5-ASA, e.g., mesalamine). CD does not respond reliably to 5-ASAs. Moderate-to-severe IBD requires systemic corticosteroids for acute flares, followed by steroid-sparing maintenance therapy with immunomodulators (azathioprine, 6-mercaptopurine) or biologic agents (anti-TNF agents like infliximab, anti-integrin agents like vedolizumab). Surgical resection is curative for UC (total proctocolectomy) but is non-curative and reserved for complications (obstruction, perforation, refractory fistulas) in CD.

Irritable Bowel Syndrome (IBS)

Irritable bowel syndrome (IBS) is a functional GI disorder characterized by abdominal pain and altered bowel habits without structural abnormalities. Diagnosis is made using the Rome IV criteria: recurrent abdominal pain at least 1 day per week in the last 3 months, associated with two or more of the following: related to defecation, associated with a change in stool frequency, or associated with a change in stool appearance. Crucially, "alarm features" must be absent before diagnosing IBS. These include onset after age 50, nocturnal diarrhea, rectal bleeding, weight loss, unexplained iron deficiency anemia, or a family history of organic GI disease (e.g., CRC, IBD, celiac disease). Management is tailored to the predominant bowel habit:

• IBS-D (Diarrhea-predominant): Loperamide (first-line for diarrhea), eluxadoline, or rifaximin (a non-absorbable antibiotic). Tricyclic antidepressants (TCAs) like amitriptyline are used at low doses for their anticholinergic, anti-diarrheal, and visceral analgesic properties.
• IBS-C (Constipation-predominant): Soluble fiber supplementation (psyllium), osmotic laxatives (polyethylene glycol), or secretory agents such as lubiprostone or linaclotide (guanylate cyclase-C agonists).
• All subtypes: Dietary modifications, including a low-FODMAP diet (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) and stress reduction.

Acute Diverticulitis

Diverticulosis is the presence of colonic outpouchings, most commonly in the sigmoid colon. Acute diverticulitis occurs when a diverticulum becomes microperforated, leading to localized inflammation.

• Presentation: Left lower quadrant abdominal pain, low-grade fever, and leukocytosis.
• Diagnosis: The gold standard is a CT scan of the abdomen and pelvis with intravenous contrast, which reveals colonic wall thickening, fat stranding, and potentially complications (abscess, free air).
• Contraindications: Avoid colonoscopy and barium enema in the acute setting due to the high risk of converting a microperforation into a free perforation. Colonoscopy should be scheduled 6 to 8 weeks after the resolution of symptoms to rule out underlying malignancy.
• Management: Uncomplicated diverticulitis (no abscess or perforation) in a reliable patient without systemic symptoms is managed outpatient with a clear liquid diet and oral antibiotics (e.g., ciprofloxacin plus metronidazole, or amoxicillin-clavulanate). Complicated diverticulitis requires hospitalization:
  • Abscess: If <3 cm, treat with IV antibiotics. If >=3 cm, perform CT-guided percutaneous drainage.
  • Perforation/Peritonitis: Requires emergent surgical intervention (Hartmann procedure: resection of the diseased sigmoid colon with a temporary end colostomy and rectal stump).

Lower Gastrointestinal Bleeding (LGIB)

Lower GI bleeding originates distal to the ligament of Treitz, presenting as hematochezia.

• Etiology: Diverticulosis is the most common cause of painless, brisk hematochezia. Angiodysplasia (vascular ectasia) is another common cause, frequently associated with aortic stenosis (Heyde syndrome) and end-stage renal disease. Other causes include ischemic colitis (presents with cramping abdominal pain followed by bloody diarrhea, typically at watershed areas like the splenic flexure), hemorrhoids, and colorectal neoplasia.
• Management: Ensure hemodynamic stability. Place two large-bore IVs and resuscitate. Perform colonoscopy after a rapid colonic purge. If hemodynamics are unstable and bleeding is too rapid for colonoscopy, perform CT angiography to localize the source, or a technetium-99m labeled RBC scan if bleeding is intermittent. Embolization or emergent surgical resection is indicated if bleeding is refractory.

Colorectal Cancer (CRC) Screening Guidelines

USPSTF guidelines for CRC screening in average-risk individuals are:

• Initiation: Age 45.
• Discontinuation: Screen routinely until age 75; individualize decisions from 76 to 85.
• Screening Modalities: Colonoscopy every 10 years, annual fecal immunochemical test (FIT) or guaiac-based fecal occult blood test (gFOBT), FIT-DNA (Cologuard) every 3 years, or CT colonography every 5 years.
• High-Risk Individuals: For patients with a first-degree relative diagnosed with CRC or an advanced adenoma at age <60, or two first-degree relatives at any age: initiate colonoscopy at age 40 (or 10 years before the youngest affected relative's diagnosis, whichever is earlier) and repeat every 5 years.
• IBD Surveillance: For patients with UC or Crohn colitis, screening colonoscopy should begin 8 years after symptom onset and be repeated every 1 to 3 years with random biopsies to monitor for dysplasia.