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Crohn's disease (CD) is often more extensive in children compared with adults and requires a tool using magnetic resonance enterography (MRE) for assessing inflammation in the entire bowel. To that end, Gili Focht, MSc, MBA, of the Juliet Keidan Institute of Pediatric Gastroenterology, Hepatology, and Nutrition at the Hebrew University of Jerusalem, and an international team of researchers developed and validated the Pediatric Inflammatory Crohn's Magnetic Resonance Enterography Index (PICMI), which evaluates transmural inflammation in all segments of the intestine and without the use of rectal contrast agents.

Focht discussed the group's findings from the ImageKids study, which were recently published in , with the Reading Room.

What was the clinical background that led to your group's undertaking this study?

Focht: Improving long-term outcomes in CD is associated with attainment of transmural healing. This requires close monitoring of disease activity and early medical intervention. Transmural inflammation in CD is frequently assessed via MRE. While several indices have been developed to assess transmural inflammation in adult CD patients focusing on the large bowel and terminal ileum, there was no validated tool for pediatric CD patients. Pediatric CD is more often panenteric, including the proximal small bowel, and thus any scoring system in children needs to reflect the entire bowel length.

In addition, the acceptable adult indices require either the use of gadolinium-based contrast agents and/or the rectal enema, which are less acceptable in children. This led our group to initiate the ImageKids study and specifically the development of the PICMI.

What did the study aim to clarify or improve on?

Focht: The ImageKids study aimed to develop, validate, and evaluate the PICMI to reflect the degree of transmural inflammation in children with CD. The purpose of the index is to be both discriminative at a single timepoint and evaluative, meaning to show responsiveness to change over time.

How did it differ from previous imaging methodologies for childhood CD?

Focht: The PICMI is the first tool developed to assess transmural inflammation in children with CD using MRE. It reflects the inflammation burden of the entire bowel length and does not require the use of rectal enemas or sequences based on gadolinium contrast agents, which have been associated with deposition in the brain.

Prior to the development process, the ImageKids group performed an extensive literature review, a Delphi panel of pediatric radiologists, and a cross-sectional study to select the relevant items for the PICMI development. All MREs in the study were read both locally by the site radiologists and centrally by a team of four central radiologists.

Who and where were the participants, both researchers and children?

Focht: The ImageKids study is an international investigator-initiated study held in 22 sites in Europe, North America, Asia, and Australia. Each site had both a leading pediatric gastroenterologist and a leading pediatric radiologist. A total of 240 children, 6 to 18 years old, diagnosed with CD met the eligibility criteria, of whom 116 were followed through 18 months.

To ensure inclusion of the full breadth of disease stages, patients were recruited by strata of disease duration: 20% were 0 to 3 months from diagnosis, 20% were 3 to 24 months from diagnosis, 20% were 24 to 36 months from diagnosis, and 40% were over 36 months from diagnosis. All patients underwent an ileocolonoscopy and MRE together with biosampling at enrollment and had repeat MRE and biosampling at 18 months.

What were the principal findings and have they impacted practice at your center?

Focht: We completed the development, validation, and evaluation of the PICMI in a large pediatric CD cohort. The items selected for PICMI were bowel wall thickening, wall diffusion-weighted imaging, ulceration, mesenteric edema, and comb sign.

The PICMI had high interobserver and test-retest reliability with interclass correlation coefficients of 0.84 (95% CI 0.79-0.87) and 0.81 (95% CI 0.65-0.90), respectively (both P<0.001). Excellent responsiveness was found at repeated visits with 116 MREs (area under the ROC curve 0.96, 95% CI 0.93-0.99). Both minimally important difference in the total PICMI score and cutoff values to determine severity of transmural inflammation were set to be used in the pediatric CD population. We are currently developing an online tool that will enable PICMI calculation for clinicians based on MRE results.

What were the main study limitations?

Focht: Multicenter international studies always lead to some degree of heterogeneity between sites -- such as radiologists, gastroenterologists, MRI machines, and quality of MREs -- though in this case the multicenter setting serves as an advantage, as a single center-developed index might not reflect the real-life variability and might have lower external validity.

What still remains to be determined before use of this imaging method becomes widespread?

Focht: The PICMI can already be used now as a reliable, valid, and responsive tool and can be applied both in clinical practice and clinical trials. As every tool, it is subject to ongoing evaluation through its use in subsequent studies.

You can read the abstract of the study here, and about the clinical implications of the study here.