In a 13-year-old girl with Crohn disease presenting with chronic diarrhea, altered bowel habits for 3–4 months and colonoscopy showing transmural inflammation, what is the first‑line therapy for induction of remission?

First-Line Treatment for Pediatric Crohn's Disease with Transmural Inflammation

For this 13-year-old girl with transmural inflammation on colonoscopy, systemic corticosteroids (Option A) are the first-line treatment for induction of remission, unless high-risk features are present—in which case infliximab should be initiated immediately.

Risk Stratification Determines Treatment Choice

The critical first step is identifying whether this patient has high-risk disease features that would mandate immediate anti-TNF therapy rather than corticosteroids:

High-risk features include: 1, 2

• Perianal fistulizing disease (present in 15-25% of pediatric cases)
• Severe growth retardation or delayed puberty (especially Tanner stages 2-3)
• Deep ulcerations on endoscopy
• Extensive upper GI and proximal small bowel involvement
• Stricturing or penetrating disease behavior
• Need for corticosteroids at diagnosis (paradoxically indicates poor prognosis)

Standard First-Line Therapy (No High-Risk Features)

Systemic corticosteroids are the most effective agents for rapidly inducing remission in active pediatric Crohn's disease, producing clinical improvement within days to weeks in the majority of patients. 1 The evidence supporting this is strong and comes from the American College of Radiology guidelines. 1

• Remission rates at 12 weeks are comparable whether induction is achieved with systemic corticosteroids or anti-TNF biologics, indicating both achieve similar short-term outcomes. 1
• Corticosteroids must be discontinued after achieving remission (generally 8-12 weeks) and should never be used for long-term maintenance. 1
• After remission, transition to thiopurine maintenance therapy (azathioprine 2-2.5 mg/kg/day or 6-mercaptopurine 1-1.5 mg/kg/day). 1

When to Choose Infliximab First-Line (High-Risk Disease)

If high-risk characteristics are present, early initiation of anti-TNF therapy (infliximab) is recommended rather than waiting for failure of corticosteroids. 1, 2

• The European Society of Pediatric Gastroenterology, Hepatology and Nutrition specifically recommends that pediatric patients with severe growth retardation or delayed puberty initiate anti-TNF therapy immediately as first-line treatment, representing a top-down approach to preserve remaining growth potential. 2
• The American Gastroenterological Association recommends anti-TNF therapy be initiated directly without attempting corticosteroids first when severe growth retardation is present in Tanner stages 2-3. 2
• Complications such as strictures, fistulae, or intra-abdominal abscesses should prompt a shift from corticosteroid induction to early anti-TNF biologic therapy. 1

Why Not Methotrexate?

Methotrexate (Option C) is unsuitable for initial induction therapy. 1

• Methotrexate is considered a second-line option for maintenance or after thiopurine failure. 1
• Its therapeutic effect typically requires 2-3 months, making it completely inappropriate for acute induction when rapid symptom control is needed. 1

Clinical Algorithm

For this specific case:

1. Assess for high-risk features (growth charts, Tanner staging, perianal examination, review colonoscopy for deep ulcers/strictures/fistulae) 1, 2

2. If NO high-risk features present:

   • Start systemic corticosteroids for induction 1
   • Plan 8-12 week taper 1
   • Transition to azathioprine or 6-mercaptopurine for maintenance 1
   • Perform ileocolonoscopy at 6-9 months to verify mucosal healing 1

3. If ANY high-risk features present:

   • Start infliximab immediately (standard dosing: 5 mg/kg at weeks 0,2,6, then every 8 weeks) 3
   • Consider combination therapy with thiopurines in boys (lower lymphoma risk) 2
   • Continue anti-TNF as part of maintenance strategy 1

Common Pitfalls to Avoid

• Do not use corticosteroids for maintenance therapy—they are strictly for induction only and cause growth suppression in children. 1, 2
• Do not delay anti-TNF therapy in high-risk patients—waiting for corticosteroid failure worsens long-term outcomes and may compromise growth potential. 1, 2
• Do not choose methotrexate for induction—its 2-3 month onset makes it useless for acute disease control. 1
• Do not forget to monitor for mucosal healing—endoscopic healing at 6-9 months is an important treatment target. 1

Answer: A (Systemic steroids) for standard disease, or B (Infliximab) if high-risk features are identified.