Crohn's disease — clinical reference
The broader, non-surgical reference for Crohn's disease — phenotype, diagnosis, and medical (treat-to-target) management. For the surgical site, see crohnsology.org.
Phenotype & classification
Crohn's is heterogeneous; phenotyping by the Montreal classification anchors prognosis and management.
Age at diagnosis (A)
A1 <17 y · A2 17–40 y · A3 >40 y.
Location (L)
L1 ileal · L2 colonic · L3 ileocolonic · L4 isolated upper GI (modifier, may be added to L1–L3).
Behavior (B)
B1 non-stricturing/non-penetrating · B2 stricturing · B3 penetrating. Behavior evolves over time.
Perianal modifier (p)
Appended to any location/behavior when perianal disease is present (e.g., L3B3p).
ICD-10 coding
Crohn's disease is coded K50: K50.0 (small intestine), K50.1 (large intestine), K50.8 (both), K50.9 (unspecified) — with 4th/5th-character extensions for complications.
Diagnosis & monitoring
Diagnosis integrates clinical, endoscopic, histologic, radiologic, and biomarker data; objective monitoring drives treat-to-target care.
- Ileocolonoscopy with biopsies — segmental sampling; skip lesions, aphthae, cobblestoning, granulomas
- Cross-sectional enterography — MR or CT enterography for small-bowel mapping, strictures, penetrating disease
- Biomarkers — CRP and fecal calprotectin for activity and monitoring; trend rather than treat a single value
- Therapeutic drug monitoring — drug levels/antibodies to optimize biologic therapy
- Capsule / enteroscopy — selected isolated small-bowel disease (exclude stricture first)
Medical management
Modern care is target-driven (STRIDE-II): achieve clinical remission, then biomarker normalization, then endoscopic healing — escalating until targets are met.
Risk-stratified strategy
Early effective (top-down) therapy for high-risk phenotypes (young age, extensive/penetrating/perianal disease, deep ulcers, prior resection).
Biologics & small molecules
Anti-TNF, anti-integrin (vedolizumab), anti-IL-12/23 and anti-IL-23, and JAK inhibitors — selected by phenotype, comorbidity, and access.
Immunomodulators
Thiopurines/methotrexate — combination therapy or to reduce immunogenicity.
Nutrition therapy
Exclusive enteral nutrition can induce remission (first-line in pediatrics; adjunct in adults). Correct deficiencies (iron, B12, vitamin D); involve an IBD dietitian — diet is supportive care, not a substitute for disease-modifying therapy.
What's de-emphasized
Long-term corticosteroids and 5-ASA monotherapy are not durable Crohn's strategies; steroids bridge only.
Evidence & resources
Pointers to the underlying literature and guidance.
- Surgical literature — search the Crohn's surgery collections at crohnsology's literature search
- Pouch / IBD-surgery corpus — explore the curated corpus at pouchology.org
- Guidelines — ECCO, ACG, AGA, and ASCRS Crohn's disease clinical practice guidelines
- Trials referenced — LIR!C (early resection vs infliximab), POCER (post-op endoscopy-guided management), STRIDE-II (treat-to-target targets)