Natural History of Pediatric Indeterminate Colitis

Indeterminate colitis (IC), as a classification of inflammatory bowel disease, was introduced by Kent in 1970 [1] and was intended to classify colectomy specimens that had histology findings suggestive of Crohn’s disease (CD), despite a patient’s clinical history of ulcerative colitis (UC). The 2014 Porto Criteria established new terminology, inflammatory bowel disease unclassified (IBD-U), to reduce confusion among providers, researchers, and patients [2]. Contemporarily, IBD-U is used broadly for patients whose clinical, radiological, endoscopic, and histological findings provide a muddled picture. In this chapter, we review the clinical and histological criteria needed to establish the diagnosis of inflammatory bowel disease unclassified (IBD-U), describe the factors that lead to the diagnosis of IBD-U, investigate occurrence of reclassification, and review the available literature about the natural history of this classification.