Summary

ACG 2018 guideline on management of adult Crohn’s disease covers diagnosis, disease activity assessment, induction and maintenance therapy, fistulizing disease, and postoperative prevention. Therapy is stratified by disease severity and risk for progression, with emphasis on objective monitoring (endoscopy, cross-sectional imaging, fecal calprotectin, CRP) rather than symptoms alone. Anti-TNF agents (especially combination with thiopurine) are the cornerstone for moderate-to-severe disease, while 5-ASAs are largely discouraged. Vedolizumab and ustekinumab are endorsed as effective biologic alternatives, and biosimilars of infliximab/adalimumab are accepted for induction and maintenance.

Key Recommendations

Diagnose Crohn’s by integrating clinical, endoscopic, histologic, and radiographic findings — no single pathognomonic test exists; perform ileocolonoscopy with biopsies including uninvolved mucosa.
Obtain small bowel imaging (CTE or MRE) at initial workup; prefer MRE in patients <35 years or who will need serial imaging to avoid cumulative radiation.
Use fecal calprotectin, CRP, and stool studies (including C. difficile) to evaluate active symptoms; do not rely on symptoms alone — confirm with endoscopy or cross-sectional imaging.
5-ASA/mesalamine and sulfasalazine are not effective for induction or maintenance of Crohn’s; do not use them as maintenance therapy (sulfasalazine 3–6 g/day has modest efficacy only for mildly active colonic/ileocolonic disease).
Use controlled ileal-release budesonide 9 mg/day for mild-to-moderate ileocecal Crohn’s; reserve systemic corticosteroids for moderate-to-severe flares and never use steroids for maintenance.
Use anti-TNF agents (infliximab, adalimumab, certolizumab pegol) for moderate-to-severe disease and high-risk patients; combination of infliximab with a thiopurine is superior to monotherapy for induction and maintenance.
Screen for latent TB, hepatitis B, and update vaccinations (avoid live vaccines) before starting anti-TNF or other biologics.
Vedolizumab and ustekinumab are effective for induction and maintenance in moderate-to-severe Crohn’s, including in anti-TNF failures; natalizumab requires JC virus antibody testing every 6 months due to PML risk.
Drain perianal abscesses surgically before starting immunosuppression; treat complex perianal fistulas with combined seton placement plus anti-TNF (infliximab has the best evidence).
Strongly counsel smoking cessation — smoking is the only modifiable risk factor for postoperative recurrence; avoid NSAIDs which may trigger flares.
Give postoperative prophylaxis (anti-TNF preferred; thiopurines ± metronidazole as alternatives) in patients with risk factors (smokers, penetrating disease, ≥2 prior resections); perform colonoscopy at 6 months postop to assess recurrence.
Begin surveillance colonoscopy after 8 years of disease in patients with ≥30% colonic involvement; initiate at diagnosis if PSC is present; high-definition white light or chromoendoscopy are acceptable.

Thresholds & Doses

Sulfasalazine: 3–6 g/day for mild-moderate colonic/ileocolonic CD (not for isolated small bowel).
Prednisone induction: 40–60 mg/day for 1–2 weeks, then taper 5 mg/week to 20 mg, then 2.5–5 mg/week; do not exceed 60 mg/day or 3 months total.
Budesonide CIR: 9 mg/day for mild-moderate ileocecal CD induction; 6 mg/day shown to prolong time to relapse but not effective long-term maintenance.
Azathioprine: up to 2.5 mg/kg/day; 6-mercaptopurine: up to 1.5 mg/kg/day; check TPMT before initiation.
Methotrexate: 15–25 mg SC/IM weekly for induction/maintenance; 12.5–15 mg orally weekly to reduce biologic immunogenicity.
Infliximab: 5 mg/kg IV at weeks 0, 2, 6, then every 8 weeks; target trough ≥7.5 µg/mL.
Adalimumab: target trough ≥5 µg/mL; certolizumab pegol: target trough ≥20 µg/mL; certolizumab 400 mg SC every 4 weeks maintenance.
Natalizumab: 300 mg IV every 4 weeks; check anti-JC virus antibody every 6 months — do not use if positive.
Vedolizumab: 300 mg IV every 8 weeks for maintenance.
Metronidazole 10–20 mg/kg/day PO × 4–8 weeks and/or ciprofloxacin 500 mg BID × 4–8 weeks for perianal fistulas; metronidazole 20 mg/kg or 1 g/day for postoperative prophylaxis.
Fecal calprotectin >100 µg/g predicts postoperative endoscopic recurrence (sensitivity 89%); >160 µg/g predicts relapse on infliximab (sensitivity 91.7%, specificity 82.9%).
CRP >15 mg/L at baseline predicts infliximab primary nonresponse (sensitivity 67%, specificity 65%).
CDAI: <150 remission; 150–220 mild; 220–450 moderate-severe; >450 severe/fulminant.
SES-CD: 0–2 remission, 3–6 mild, 7–15 moderate, ≥16 severe.
Colorectal cancer surveillance: start after 8 years of disease with ≥30% colonic involvement; at diagnosis if PSC present.
Capsule retention risk: 0–5.4% in suspected CD — use patency capsule or small bowel imaging first if obstructive symptoms.

Citations

Diagnosis section — ileocolonoscopy with biopsies and small bowel imaging as initial workup
Imaging studies — MRE preferred over CTE in patients <35 years and those needing serial imaging
Working definitions of disease activity — CDAI and SES-CD thresholds for remission, mild, moderate, severe
Mild-to-moderately severe disease/Mesalamine — 5-ASA not effective for CD induction or maintenance
Moderate-to-severe disease/Anti-TNF agents — combination therapy (infliximab + azathioprine) superior to monotherapy (SONIC, ref 221)
Fistulizing Crohn’s Disease/Perianal — surgical drainage of abscess before immunosuppression; seton + infliximab for complex fistulas
Postoperative Crohn’s Disease — anti-TNF as first-line prophylaxis in high-risk patients; risk factors include smoking, penetrating disease, ≥2 resections
Maintenance therapy — corticosteroids and 5-ASAs not recommended; anti-TNF, thiopurines, methotrexate, vedolizumab, ustekinumab effective