How should inflammatory bowel disease be diagnosed and managed?

Inflammatory Bowel Disease: Diagnosis and Management

Inflammatory bowel disease should be diagnosed through ileocolonoscopy with biopsies combined with intestinal ultrasound or magnetic resonance enterography, followed by disease-specific treatment with aminosalicylates for mild-moderate ulcerative colitis or corticosteroids/advanced therapies for moderate-severe disease, with lifelong maintenance therapy to prevent relapse and reduce colorectal cancer risk. 1

Diagnostic Approach

Initial Evaluation

The diagnosis of IBD requires a combination of clinical assessment, laboratory markers, endoscopy with histology, and cross-sectional imaging 1. Ileocolonoscopy with biopsies remains the cornerstone diagnostic tool and should always include terminal ileum intubation unless contraindicated 1.

Key endoscopic findings to differentiate:

• Crohn's disease: Skip lesions, rectal sparing, terminal ileum involvement, aphthous ulcers, deep/serpiginous ulcers, cobblestoning 1
• Ulcerative colitis: Continuous inflammation from rectum proximally, granularity, loss of vascular pattern, friability, superficial ulcerations, clear demarcation line 1

Essential Diagnostic Tests

Laboratory markers:

• Fecal calprotectin is superior to C-reactive protein for detecting IBD, with 88% sensitivity and 92% specificity at cutoff ≤50 μg/g 1. It correlates better with endoscopic activity than symptom-based indices and is more accurate in ulcerative colitis than Crohn's disease 1.
• CRP and complete blood count for baseline inflammatory assessment 2

Imaging:

• Intestinal ultrasound or MRE should be performed alongside colonoscopy for initial diagnosis 1
• Ultrasound shows 95% sensitivity, 77% specificity for established Crohn's disease when combining bowel wall thickness with color Doppler 1
• Capsule endoscopy is recommended for suspected Crohn's disease with negative colonoscopy and imaging 1

Management of Ulcerative Colitis

Active Disease Treatment

Mild to moderate extensive/left-sided UC:

• First-line: Oral aminosalicylates (mesalazine 2-4 g daily, olsalazine 1.5-3 g daily, or balsalazide 6.75 g daily) 2
• If inadequate response: Add prednisolone 40 mg daily, taper gradually over 8 weeks 2
• Avoid sulfasalazine as first-line due to higher side effect profile; reserve for patients with reactive arthropathy 2

Active distal UC (proctitis to sigmoid):

• Optimal therapy: Topical mesalazine 1 g daily (suppositories for proctitis, foam/liquid enemas for more proximal disease) PLUS oral mesalazine 2-4 g daily 2
• This combination is more effective than either agent alone 2
• Topical corticosteroids are less effective than topical mesalazine; use only if mesalazine intolerant 2

Severe UC (meeting Truelove and Witts criteria):

• Immediate hospital admission for joint gastroenterology-surgical management 2
• Intravenous corticosteroids (hydrocortisone 400 mg/day or methylprednisolone 60 mg/day)
• Critical monitoring: Daily physical exam for peritoneal signs, vital signs 4x daily, stool chart, FBC/CRP/electrolytes/albumin every 24-48 hours 2
• Daily abdominal radiograph if colonic dilatation >5.5 cm detected 2
• IV fluid/electrolyte replacement, blood transfusion to maintain hemoglobin >10 g/dL 2
• Subcutaneous heparin for thromboembolism prophylaxis 2
• Inform patients of 25-30% colectomy risk 2
• Consider ciclosporin for severe steroid-refractory colitis 2

Maintenance Therapy

Lifelong maintenance is generally recommended for all UC patients, especially those with left-sided/extensive disease and those with distal disease relapsing >1x/year 2. Aminosalicylates, azathioprine 1.5-2.5 mg/kg/day, or mercaptopurine 0.75-1.5 mg/kg/day should be used to reduce relapse risk and potentially reduce colorectal cancer risk 2.

Steroid-dependent patients: Transition to azathioprine or mercaptopurine; long-term steroids are undesirable 2

Management of Crohn's Disease

Active Disease Treatment

The 2025 British guidelines emphasize early advanced therapy (biologics/small molecules) for moderate-severe disease rather than traditional step-up approaches 3. This represents a significant shift from older 2004 guidelines.

Mild ileocolonic Crohn's:

• High-dose mesalazine 4 g daily may be sufficient 2

Moderate to severe disease:

• Prednisolone 40 mg daily for patients requiring prompt response or those failing mesalazine 2
• Taper over 8 weeks; rapid reduction causes early relapse 2
• Budesonide 9 mg daily for isolated ileocecal disease (marginally less effective than prednisolone) 2
• Consider early advanced therapy initiation whenever prescribing systemic corticosteroids 3

Severe disease:

• IV steroids (hydrocortisone 400 mg/day or methylprednisolone 60 mg/day) 2
• Concomitant IV metronidazole often advisable to distinguish active disease from septic complications 2

Alternative/adjunctive therapies:

• Elemental/polymeric diets less effective than corticosteroids but useful for patients with contraindications or preferring to avoid steroids 2
• Total parenteral nutrition appropriate for complex fistulating disease 2

Perianal Fistulating Disease

First-line: Metronidazole 400 mg TDS and/or ciprofloxacin 500 mg BD 2

Second-line: Azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day after excluding distal obstruction and abscess 2

Refractory disease: Infliximab (5 mg/kg at 0,2,6 weeks) as part of strategy including immunomodulation and surgery 2

Surgery (Seton drainage, fistulectomy, advancement flaps) appropriate for persistent/complex fistulae combined with medical treatment 2

Maintenance Therapy

Most important intervention: All smokers must be strongly advised to stop with counseling, nicotine patches, or substitutes offered 2

Pharmacologic options:

• Azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day are effective but reserved as second-line due to toxicity 2
• Mesalazine has limited benefit, ineffective at <2 g/day or for those needing steroids for induction 2
• Methotrexate 15-25 mg IM weekly effective for patients responding to IM methotrexate during active disease; appropriate for azathioprine/mercaptopurine failures 2
• Infliximab 5-10 mg/kg every 8 weeks effective for up to 44 weeks in responders; best used with immunomodulation 2
• Corticosteroids including budesonide are NOT effective for maintenance 2

Critical Pitfalls to Avoid

1. Do not delay corticosteroids in severe UC while awaiting stool microbiology to exclude infection 2
2. Avoid repeated steroid courses unless futility of other therapies established and surgery not feasible 3
3. Never use corticosteroids for maintenance in either UC or Crohn's disease 2, 3
4. Do not use mesalazine alone for distal UC when combination with topical therapy is more effective 2
5. Recognize steroid-dependent patients early and transition to immunomodulators 2
6. Monitor severe UC patients intensively with daily clinical assessment and frequent labs/imaging to identify surgical candidates 2

Important Nuances

The evidence base shows a clear evolution: while the 2004 Gut guidelines [2-2] established the foundation for IBD management with aminosalicylates and corticosteroids, the 2025 British guidelines 3 now advocate for early advanced therapy in moderate-severe Crohn's disease, reflecting improved understanding of disease trajectory and treatment efficacy. However, for ulcerative colitis, the aminosalicylate-first approach remains appropriate for mild-moderate disease.

The distinction between UC and Crohn's management is critical: UC responds well to aminosalicylates and benefits from lifelong maintenance therapy, while Crohn's disease requires more aggressive early intervention with biologics for moderate-severe disease and smoking cessation as the single most important maintenance factor.