XV. 2 Profile 2: Inflammatory Bowel Disease – Undifferentiated / Combined (IBD)
When inflammatory bowel disease doesn't fit neatly into colitis or Crohn's, this profile guides a cautious, combined approach to FMT.
| Parameter | IBD-specific detail |
|---|---|
| Evidence level | ★★★☆☆ Moderate. Ulcerative colitis (Profile 2) and Crohn's disease (Profile 3) are separately profiled with condition-specific evidence. This combined IBD profile applies to patients with IBD-unclassified (IBD-U), overlap phenotypes, or clinical presentations that do not clearly fit UC or CD criteria. Evidence base derives from UC and CD trials; direct IBD-U FMT trial data are limited. |
| Mechanism of dysbiosis | Core IBD dysbiosis: reduced microbial diversity; Firmicutes/Bacteroidetes ratio inversion; Faecalibacterium prausnitzii depletion; Proteobacteria bloom (especially adherent-invasive E. coli in CD-type); impaired colonization resistance; mucosal barrier dysfunction; dysregulated innate and adaptive immune responses to luminal microbiota. |
| Primary microbiota targets | Restore F. prausnitzii and butyrate-producing Lachnospiraceae. Suppress adherent-invasive E. coli. Rebuild colonization resistance. Normalise mucosal immune tone (Treg/Th17 balance). Restore short-chain fatty acid production for colonocyte energy supply. |
| Protocol modification | Full 4-phase protocol. Classification review recommended before FMT initiation – if subsequent clinical or histological features allow reclassification to UC or CD, apply the relevant disease-specific profile. Active severe disease: IBD-U patients with severe activity (CDAI >300 or Mayo ≥9) should be stabilised before FMT. Biologics and immunosuppressants: continue at stable doses; do not alter during FMT unless directed by gastroenterologist. |
| Minimum transfer duration | 60 days minimum; 90 days preferred for IBD-U given diagnostic uncertainty. Duration should be reassessed at 60 days in context of symptom trajectory and any reclassification. |
| Priority exposome focus | Dietary fiber (soluble and fermentable; caution with insoluble fiber during flares). Reduce ultra-processed food, emulsifiers, and artificial sweeteners (all documented to worsen IBD dysbiosis). Anti-inflammatory dietary pattern. Stress reduction – HPA axis directly worsens mucosal barrier integrity. Sleep quality – poor sleep amplifies IBD inflammatory cycles. |
| Expected response timeline | Stool frequency and consistency: improvement within 2–4 weeks in UC-type presentations; slower in CD-type (4–8 weeks). Inflammatory biomarkers (CRP, fecal calprotectin): 4–8 weeks. Endoscopic mucosal healing: 12–24 weeks. Quality of life: 4–12 weeks. |
| Warning signs (IBD-specific) | Fever ≥38°C (IBD flare or infectious complication – immediate clinical contact). Significant rectal bleeding or change in stool character. Severe abdominal pain. Any symptoms meeting Tier 1 emergency criteria (see Chapter II). Extraintestinal manifestations worsening (joints, eyes, skin) – may reflect systemic inflammatory activity. New perianal symptoms (CD-type complication risk). |
Table 13 – Clinical profile: Inflammatory Bowel Disease – Undifferentiated (IBD-U) # Protocol parameters, evidence level, and clinical modifications specific to IBD-U.
Note: Patients with IBD-U should have diagnostic reclassification reviewed at 6–12 months; updated classification should be used to guide ongoing protocol selection. This profile is not a substitute for UC-specific or CD-specific management where classification is clear.
The 2024 ECCO consensus (Caenepeel et al., J Crohn Colitis) categorizes FMT as conditionally recommended in UC, not recommended in Crohn's disease, and emerging evidence for the UC + biologic-refractory subgroup. The IBD-specific FMT protocol differs substantially from the rCDI protocol: multi-dose induction (colonoscopic + 6–8 weeks capsule consolidation), multi-donor pooling is preferred to maximize strain diversity, and donor–recipient compatibility assessment is mandatory.
Key Clinical Decision Points in IBD-FMT
| Parameter | Specification |
|---|---|
| Optimal indication window | Mild-moderate UC, biologic-naïve or after first biologic failure |
| Delivery route | Colonoscopic induction + capsule consolidation (≥6 weeks) |
| Donor choice | Multi-donor pool (3–5 donors) in UC; super-donor for IBS-overlap cases |
| Expected response | UC: 36% week-8 clinical remission; sustained 5-year remission: 26% |
| Early response markers | Calprotectin reduction ≥50% by week 4 |
| Non-response management | Biologic combination (vedolizumab[G]) |
| Long-term monitoring | Annual clinical assessment, calprotectin, fecal microbiome (strain-level) |
The vedolizumab + FMT combination is a mechanistically promising direction in biologic-refractory ulcerative colitis: vedolizumab's blockade of α4β7-MAdCAM-1 locally reduces inflammatory T-cell trafficking, while FMT restores colonization resistance[G] and butyrate production. No randomised trial of this combination is available, so we give no response rate.
In Crohn's disease (see XV.5), the evidence is weaker: reviews link donor strain engraftment and the return of butyrate-producing taxa to more favourable outcomes, but a strain-level Faecalibacterium prausnitzii Phylogroup II predictor for the ileocolonic, biologic-naïve subgroup has not yet been validated [478], [793].
References
[478] Sokol H, Landman C, Seksik P et al. Fecal microbiota transplantation to maintain remission in Crohn's disease: a pilot randomized controlled study. Microbiome. 2020. Link
Randomized, single-blind, sham-controlled pilot trial of FMT in adults with colonic or ileo-colonic Crohn's disease in steroid-induced clinical remission. Patients were randomized at remission to receive FMT or sham transplantation during colonoscopy; corticosteroids were tapered and follow-up colonoscopy performed at week 6. The trial provides the first randomized data on FMT for maintaining remission in CD, with modest signals supporting microbial engraftment as a candidate driver of clinical response and informing larger confirmatory studies.
[793] Fehily S, Basnayake C, Wright E, Kamm M. Fecal microbiota transplantation therapy in Crohn's disease: Systematic review. Journal of gastroenterology and hepatology. 2021. Link
FMT in Crohn's disease — systematic review — 15 studies (2 RCTs, 13 cohorts). Multiple FMT showed higher early response rate. Upper GI route early efficacy 75–100% vs. lower 30–58%. No serious adverse events occurred.