Neutrophil-only histological assessment of ulcerative colitis correlates with endoscopic activity and predicts long-term outcomes in a multicenter study

Backgrounds and aims: Absence of neutrophils is the minimum standard to consider histological remission of ulcerative colitis (UC). The PICaSSO Histological remission Index (PHRI) is a new simple index for UC based only on the detection of neutrophils. We evaluate PHRI's correlation with endoscopy and its prognostic value compared to other established indices. Methods: Consecutive patients with UC underwent colonoscopy at 2 referral centres (Birmingham, UK and Milan, Italy) and were followed up for 2 years. Correlation between histology (PHRI, Nancy [NHI] and Robarts [RHI]) and endoscopy (Mayo Endoscopic Score [MES]; Ulcerative Colitis Severity Endoscopic Index of Severity [UCEIS], and PICaSSO score) was calculated as Spearman coefficients. Diagnostic performance of endoscopy was assessed with ROC curves and outcome stratification with Kaplan-meier curves. Results: 192 patients with UC were enrolled, representing all grades of endoscopic severity. Correlation between histology and endoscopy did not differ significantly when using PHRI instead of NHI or RHI. In particular, PHRI's correlation with MES, UCEIS and PICaSSO was 0.745, 0.718, and 0.694, respectively. Endoscopically-assessed remission reflected the absence of neutrophils (PHRI = 0) with areas under the ROC curve of 0.905, 0.906, and 0.877 for MES, UCEIS, and PICaSSO, respectively. The hazard ratio for disease flare between patients in histological activity/remission was statistically similar (p>0.05) across indexes (2.752, 2.706, and 2.871 for RHI, NHI, and PHRI, respectively). Conclusion: PHRI correlates with endoscopy and stratifies risk of relapse similarly to RHI and NHI. Neutrophil-only assessment of UC is a simple yet viable alternative to established histological scores.