A Novel Method for Quantifying Intestinal Inflammatory Burden in Inflammatory Bowel Disease Using Register Data.

Background: The Swedish Quality Register for Inflammatory Bowel Disease (SWIBREG) contains clinical data for the study of inflammatory bowel disease (IBD). The Epidemiology Strengthened by histoPathology Reports in Sweden (ESPRESSO) cohort was recently established for the study of gastrointestinal histopathology. We aimed to develop and validate a histology score from ESPRESSO using clinical information from SWIBREG, and secondarily, to evaluate the association of the score on IBD-related hospitalization.

Methods: In a nationwide, population-based cohort study of patients with IBD during 1969-2017, we linked endoscopic inflammation in SWIBREG with histologic inflammation in ESPRESSO. We established a clinically interpretable model for predicting the endoscopic score from histology using scalable Bayesian rule lists to define a SNOMED-based histology score applicable to the ESPRESSO cohort. We also assessed the impact of baseline endoscopic and histology scores on time to IBD-related hospitalization.

Results: We identified 5225 individuals with IBD comprising 11,051 endoscopic assessments in SWIBREG linked to a histopathology record in ESPRESSO. We created predictive models to calculate a SNOMED-based histology score which predicted the endoscopic score. Split-sample validated areas under the ROC curves for the score predicting a non-zero endoscopic score were 0.80 (0.78-0.81) in UC, 0.70 (0.68-0.72) in CD, and 0.76 (0.73-0.78) in IBD-U. In a subset of 2741 individuals with an initial IBD diagnosis and a corresponding record in ESPRESSO with an endoscopic assessment in SWIBREG, the baseline endoscopic and histology scores were associated with time to IBD-related hospitalization (endoscopy log-rank UC p<0.001, CD p=0.020, IBD-U p<0.001; histology log-rank UC p=0.018, CD p=0.960, IBD-U p=0.034).

Conclusion: Histopathology data in ESPRESSO accurately predict endoscopic scores in SWIBREG. Baseline endoscopic and histologic scores were associated with time to IBD-related hospitalization, particularly in UC. The SNOMED-based histology score can be used as a measure of disease activity in future register-based IBD studies.