What is the first-line treatment for a teenage girl with chronic diarrhea, altered bowel habits, and colonoscopic findings of transmural inflamed patches consistent with Crohn disease?

First-Line Treatment for Pediatric Crohn's Disease

For this 13-year-old girl with newly diagnosed Crohn's disease (transmural inflammation on colonoscopy), systemic corticosteroids remain the first-line treatment option for inducing remission, though biologics like infliximab are increasingly used early in moderate-to-severe disease or when high-risk features are present.

Understanding the Clinical Presentation

The colonoscopic finding of transmural inflamed patches is pathognomonic for Crohn's disease, distinguishing it from ulcerative colitis which shows only mucosal/submucosal inflammation 1, 2. This transmural inflammation, along with the chronic diarrhea and altered bowel habits over 3-4 months, confirms active Crohn's disease requiring induction therapy 3.

Treatment Algorithm for Newly Diagnosed Pediatric Crohn's Disease

Initial Disease Severity Assessment

Before selecting therapy, you must determine:

• Disease extent: The colonoscopy shows colonic involvement, but you need cross-sectional imaging (MR enterography preferred in children) to assess small bowel disease 4
• Disease severity: Presence of complications (strictures, fistulae, abscesses) would shift treatment toward biologics 5
• Risk stratification: Young age at diagnosis, extensive disease, deep ulcerations, and perianal involvement predict poor outcomes requiring early aggressive therapy 6, 3

Treatment Selection Based on Disease Severity

For Mild-to-Moderate Disease:

• Systemic corticosteroids (prednisone 40-60 mg daily or equivalent) are highly effective for inducing remission in 60-70% of patients 7, 8
• Treatment duration typically 8-12 weeks with gradual taper 8
• Limitation: Corticosteroids do NOT maintain remission and have significant side effects with prolonged use 7

For Moderate-to-Severe Disease or High-Risk Features:

• Anti-TNF biologics (infliximab or adalimumab) should be initiated early, with or without immunomodulators 8, 6
• Studies show biologics achieve both clinical remission AND endoscopic healing, which alters disease progression 3
• The treatment paradigm has shifted toward "top-down" therapy with early biologics in patients at risk for poor outcomes 3

Why Systemic Steroids (Option A) is the Traditional First-Line Answer

Corticosteroids remain the most effective medication for rapidly inducing remission in active Crohn's disease 5. They work within days to weeks and have decades of proven efficacy 7. However, the evidence shows treatment response at 12 weeks with either corticosteroids OR anti-TNF agents 5.

Why Infliximab (Option B) is Increasingly Used First-Line

Modern treatment guidelines favor early biologic therapy in patients with moderate-to-severe disease or risk factors for poor outcomes 3. The "treat-to-target" approach with endoscopic healing as the goal supports early biologic use 4. Infliximab achieves both symptomatic control AND mucosal healing, potentially preventing long-term complications like strictures and fistulae 3.

Why Methotrexate (Option C) is NOT First-Line

Methotrexate is an immunomodulator used primarily for maintaining remission, not inducing it 8. It takes 8-12 weeks to achieve therapeutic effect, making it inappropriate for active symptomatic disease requiring immediate control 8.

Practical Clinical Approach

For this specific patient, the answer depends on disease severity:

1. If mild-to-moderate disease without complications: Start systemic corticosteroids (prednisone 1 mg/kg/day, max 40-60 mg) for induction, then transition to maintenance therapy with immunomodulators (azathioprine/6-mercaptopurine) or biologics 8, 6

2. If moderate-to-severe disease, extensive involvement, or high-risk features: Start infliximab (5 mg/kg at weeks 0,2,6, then every 8 weeks) with or without concomitant immunomodulator 8, 3

3. Pediatric-specific consideration: Exclusive enteral nutrition (liquid diet) for 6-8 weeks is as effective as corticosteroids for inducing remission in children and avoids steroid side effects, though compliance is challenging 6

Critical Monitoring After Treatment Initiation

Regardless of initial therapy choice, implement treat-to-target monitoring 4:

• Clinical assessment with symptom scores every 3 months
• Fecal calprotectin every 3-6 months to assess inflammation 4, 6
• Endoscopic evaluation at 6-12 months to confirm mucosal healing 4
• MR enterography to assess transmural healing and detect complications 5

Common Pitfalls to Avoid

• Do not use corticosteroids for maintenance therapy - they are ineffective and cause significant toxicity with prolonged use 7, 8
• Do not delay biologics in high-risk patients - early aggressive therapy prevents irreversible bowel damage 3
• Do not forget to rule out infections - obtain stool studies including C. difficile before starting immunosuppression 4
• Do not ignore extraintestinal manifestations - assess for arthritis, skin lesions, and eye inflammation which occur in up to 25% of patients 4, 7

The most defensible answer for a board examination context is Option A (Systemic steroids), as they remain the traditional first-line induction therapy with the fastest onset of action. However, in contemporary clinical practice, Option B (Infliximab) is increasingly appropriate as first-line therapy for moderate-to-severe pediatric Crohn's disease.