What is the scoring range of the Perianal Disease Activity Index (PDAI) and what constitutes a clinically significant improvement

What is known

- PDAI sums five 5-point Likert items (0–4 each) for a total range of 0–20, higher scores indicating more severe disease. ^1–3 - A cutoff of 4 discriminates active from inactive perianal disease with 87% accuracy; ≤4 inactive, >4 active. ^2–5 - In the original McMaster validation, PDAI improved by a mean of ~3 points when perianal disease had clinically improved, and was stable in clinically stable patients. ⁶

What is unknown / caveats

- No formally validated minimal clinically important difference for PDAI improvement - A PDAI of 0 (remission) requires complete closure of all cutaneous orifices, not just absence of inflammation - The ~3-point change reflects an observed difference in improved patients, not a validated responder threshold.

## References

1. Gecse KB, Sebastian S, Hertogh G, Yassin NA, Kotze PG, Reinisch W, Spinelli A, Koutroubakis IE, Katsanos KH, Hart A, van den Brink GR, Rogler G, Bemelman WA. Results of the Fifth Scientific Workshop of the ECCO [II]: Clinical Aspects of Perianal Fistulising Crohn's Disease-the Unmet Needs. J Crohns Colitis. 2016;10(7):758-65. PMID: 26826183.

2. Rencz F, Lakatos PL, Gulácsi L, Brodszky V, Kürti Z, Lovas S, Banai J, Herszényi L, Cserni T, Molnár T, Péntek M, Palatka K. Validity of the EQ-5D-5L and EQ-5D-3L in patients with Crohn's disease. Qual Life Res. 2019;28(1):141-152. PMID: 30225788.

3. Villa C, Pompili G, Franceschelli G, Munari A, Radaelli G, Maconi G, Cornalba GP. Role of magnetic resonance imaging in evaluation of the activity of perianal Crohn's disease. Eur J Radiol. 2012;81(4):616-22. PMID: 21316171.

4. Ma K, Hu C, Fu Y, Liu Y, Weng F, Yao Y, Wang C. Metabolic profiles of amino acids in patients with crohn's disease-associated perianal fistulas and cryptoglandular anal fistulas. Sci Rep. 2026;16(1):3366. PMID: 41554770.

5. Losco A, Viganò C, Conte D, Cesana BM, Basilisco G. Assessing the activity of perianal Crohn's disease: comparison of clinical indices and computer-assisted anal ultrasound. Inflamm Bowel Dis. 2009;15(5):742-9. PMID: 19023861.

6. Irvine EJ. Usual therapy improves perianal Crohn's disease as measured by a new disease activity index. McMaster IBD Study Group. J Clin Gastroenterol. 1995;20(1):27-32. PMID: 7884173.

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_Draft — generated by the IBDology RAG and not yet clinician-reviewed. Answers are grounded in the retrieved literature listed above; a high faithfulness score means the answer matches its sources, not that the sources are correct._