What are the differences in diagnosis and treatment between Crohn's disease and ulcerative colitis in an adult patient with a history of gastrointestinal symptoms?

Distinguishing Crohn's Disease from Ulcerative Colitis

Diagnostic Approach

Perform a complete ileocolonoscopy with biopsies from at least five sites (including terminal ileum and rectum) combined with cross-sectional imaging (MRI or CT enterography) to definitively differentiate these conditions. 1, 2

Endoscopic Evaluation

• Complete ileocolonoscopy is mandatory, even if sigmoidoscopy suggests ulcerative colitis, because approximately one-third of Crohn's disease patients have small bowel involvement undetectable by limited examination 2
• Obtain at least two biopsies from five different sites: terminal ileum, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum—even from normal-appearing mucosa 1, 2
• Biopsies from unaffected areas are essential to document histologically the spared segments between inflammatory areas, which characterizes Crohn's disease 1, 2

Imaging Requirements

• Systematically perform MRI or CT enterography in all patients at diagnosis to evaluate small bowel involvement and exclude complications 1, 2
• This imaging is indispensable because small intestine disease cannot be detected by colonoscopy and strongly suggests Crohn's disease over ulcerative colitis 2

Laboratory Testing

• Obtain complete blood count, CRP, albumin, liver function tests, iron status, renal function, and vitamin B12 1, 2
• Measure fecal calprotectin (sensitivity 93%, specificity 96% for inflammatory bowel disease; optimal threshold 100 μg/g) 1, 2
• Always perform stool cultures and Clostridium difficile toxin assay to exclude infectious mimics before finalizing the diagnosis 3, 2

Key Distinguishing Features

Anatomical Distribution

Ulcerative colitis:

• Begins in the rectum and extends proximally in a continuous, uninterrupted pattern with gradually decreasing inflammation severity 1, 2
• Rectal involvement present in >97% of untreated cases 1, 2

Crohn's disease:

• Shows patchy, discontinuous distribution with skip lesions throughout the gastrointestinal tract 1, 2
• Rectal sparing is common (occurs in only up to 3% of ulcerative colitis patients) 1, 2

Depth of Inflammation

Ulcerative colitis:

• Inflammation limited to mucosa and occasionally submucosa 1, 2, 4

Crohn's disease:

• Transmural inflammation affecting all layers of the intestinal wall 1, 2, 4

Histological Features

Crohn's disease:

• Non-caseating granulomas present (absent in ulcerative colitis) 1, 2, 4
• Variable intensity of inflammatory infiltrate within and between biopsies 1, 2

Ulcerative colitis:

• Crypt abscesses more common (41% vs 19% in Crohn's disease) 1, 2
• Diffuse inflammatory infiltrate without variations in intensity 1, 2
• Basal plasmacytosis, diffuse crypt atrophy and distortion, villous surface irregularity, and mucus depletion 2

Associated Conditions

• Primary sclerosing cholangitis is more commonly associated with ulcerative colitis than Crohn's disease 1, 2
• Perianal fistulas and ulcers are rare in ulcerative colitis but common in Crohn's disease 4

Indeterminate Colitis

In 5-15% of cases, endoscopic and histological evaluation cannot distinguish between Crohn's colitis and ulcerative colitis 1, 2, 5, 6

When Initial Evaluation is Inconclusive:

• Perform capsule endoscopy of the small intestine, which can establish a definitive diagnosis of Crohn's disease by demonstrating small bowel lesions in 17-70% of patients with unclassified inflammatory bowel disease 1, 2
• A negative capsule endoscopy does not definitively exclude a future diagnosis of Crohn's disease 1, 2

Diagnostic Pitfalls:

• Rectal sparing can occur in ulcerative colitis patients who have received empirical topical therapy, potentially mimicking Crohn's disease 2
• A "cecal patch" (isolated peri-appendiceal inflammation) and backwash ileitis (occurring in up to 20% of extensive colitis) can occur in ulcerative colitis but should prompt small bowel evaluation if other features are atypical 2
• Uneven distribution of inflammation within the colon can occur in ulcerative colitis patients with long-standing disease or after treatment 2

Treatment Differences

Ulcerative Colitis

Acute severe disease:

• Intravenous corticosteroids (hydrocortisone 400 mg/day or methylprednisolone 60 mg/day) 3
• Joint medical and surgical management with daily physical examination 3
• Patients should be informed of 25-30% chance of needing colectomy 3
• Total colectomy with ileostomy results in cure 4

Maintenance therapy:

• Lifelong maintenance therapy with aminosalicylates, azathioprine, or mercaptopurine recommended for all patients, especially those with left-sided or extensive disease 3

Crohn's Disease

Active ileocolonic disease:

• Mild disease: High-dose mesalazine (4 g/daily) may be sufficient 3
• Moderate to severe disease: Oral prednisolone 40 mg daily, reduced gradually over 8 weeks 3
• Isolated ileo-caecal disease: Budesonide 9 mg daily (marginally less effective than prednisolone) 3
• Severe disease: Intravenous steroids with concomitant intravenous metronidazole when difficult to distinguish active disease from septic complications 3, 7

Key difference:

• Surgery in Crohn's disease may obtain remission of symptoms, but disease is likely to recur in the small intestine 4

Infection Management

• Clostridium difficile infection in acute severe ulcerative colitis is associated with significantly increased risk of colectomy and should be treated with oral vancomycin 3
• Administer antibiotics only in the presence of documented superinfection, intra-abdominal abscesses, or sepsis 7
• The combination of ciprofloxacin and metronidazole is most effective for infectious complications in Crohn's disease, including perianal disease and bacterial overgrowth from strictures 7