What are the initial steps a dermatologist should take to exclude inflammatory bowel disease in a child with psoriasis vulgaris before initiating anti‑interleukin‑17 therapy?

Screening for IBD Before Anti-IL-17 Therapy in Pediatric Psoriasis

Before initiating anti-IL-17 therapy in a child with psoriasis, you must screen for inflammatory bowel disease by obtaining a detailed gastrointestinal history (diarrhea, abdominal pain, bloody stools, fever), assessing for poor growth or unintentional weight loss, and measuring fecal calprotectin—if any of these are positive, refer to gastroenterology before proceeding, as IL-17 inhibitors can trigger or worsen IBD and should be avoided in patients with active disease 1, 2.

Why This Matters

Anti-IL-17 agents (secukinumab, ixekizumab, brodalumab) are contraindicated in patients with inflammatory bowel disease. Clinical trial data showed that secukinumab not only failed to improve Crohn's disease but actually caused paradoxical worsening of bowel inflammation in some patients 1. Real-world evidence confirms this risk: IL-17 inhibitors are associated with both new-onset IBD and exacerbation of existing disease 3, 4.

Specific Screening Algorithm

Step 1: Clinical History Assessment

Ask specifically about:

• Gastrointestinal symptoms: Diarrhea (present in 90.9% of IL-17-induced IBD cases), abdominal pain (57.6%), bloody diarrhea (51.5%), and fever (36.4%) 3
• Growth parameters: Poor growth velocity or unintentional weight loss 2
• Family history: IBD in first-degree relatives

Step 2: Laboratory Screening

• Fecal calprotectin: This is your most important screening tool. Elevated levels (>50 μg/g) indicate intestinal inflammation and warrant gastroenterology referral 3, 5
• Consider baseline inflammatory markers (ESR, CRP, CBC) if symptoms are present

Step 3: Risk Stratification

Children with psoriasis have a 3-4 times higher risk of IBD compared to unaffected children 2. In German database studies, the prevalence of Crohn's disease was 0.51% vs 0.14% in controls, and ulcerative colitis was 0.12% vs 0.10% 2.

What to Do Based on Findings

If Screening is Negative:

• Proceed with anti-IL-17 therapy
• Educate the family about IBD warning signs to monitor during treatment 1
• Consider repeat fecal calprotectin at 3 months, as intestinal inflammation can develop even without symptoms 6

If Screening is Positive:

• Refer to pediatric gastroenterology immediately before starting any biologic 1
• If IBD is confirmed, avoid all IL-17 inhibitors 1
• Consider alternative biologics: TNF inhibitors or IL-12/23 inhibitors (ustekinumab) are safer choices, as ustekinumab is actually FDA-approved for Crohn's disease 1

Critical Pitfalls to Avoid

Do not assume absence of symptoms means absence of risk. Studies show that IL-17 blockade can alter intestinal homeostasis toward mucosal inflammation even in asymptomatic patients, with increased fecal calprotectin and mononuclear cell infiltration occurring within 3 months 6.

Do not rely solely on clinical symptoms. Fecal calprotectin was elevated in 100% of IL-17-induced IBD cases in one analysis, often before clinical symptoms became severe 3.

Monitoring During Treatment

If you proceed with anti-IL-17 therapy after negative screening:

• The median time to IBD symptom onset is 2.9 months after starting treatment 3
• Monitor for gastrointestinal symptoms at each follow-up visit
• If IBD develops, discontinuation of IL-17 inhibitor plus corticosteroids ± TNF antagonists typically leads to remission within 4 weeks 3

Alternative Therapeutic Options

If IBD is present or develops, switch to:

• Ustekinumab (IL-12/23 inhibitor): Effective for both psoriasis and Crohn's disease 1
• TNF inhibitors: Adalimumab or infliximab treat both conditions, though paradoxical psoriasis can rarely occur 1

The strength of recommendation to avoid IL-17 inhibitors in IBD patients is Grade C (based on Level I evidence from the secukinumab trial showing disease worsening) 1.