To identify when treatment should be intensified, we must define MH, including partial MH. Of course, complete MH with scarring is acceptable as MH. But structuring occurs as the result of MH after effective remission induction therapy. How can we categorize that condition in MH (Fig. 19.3)? And the definition of partial MH should be discussed depending on the results of further several investigations. When small active lesions remain endoscopically after remission induction therapy, what is the standard of endoscopic findings for confirming the efficacy of the remission induction therapy as (partial) MH? The greater difficulty is; what is the standard of endoscopic findings to intensify the treatment during remission maintenance therapy? If we find the erosion or small ulcer, do we need to intensify the treatment? What we can do now is to continue precise objective monitoring and recognize the improving or worsening tendency of endoscopic findings.

There are some endoscopic scores for CD. CDEIS (Crohn’s disease endoscopic index of severity) or SES-CD (Simple Endoscopic Score for Crohn’s disease) are available for evaluating the endoscopic activity of ileum and colorectum. Some investigations have used a score lower than 3 for CDEIS or a score lower than 5 for SES-CD as the definition of MH [12] However, they are inconvenient to use in clinical practice because of complex calculation. And they were produced before CE or BAE. They account for four parts of colorectum but only one part of SB. In addition, SB is assessed only for the ileum. This is an imbalance. The Rutgeerts score is simple and feasible in clinical practice, but it is limited to use for neoterminal ileum in case of CD after ileocecal resection. For CE, there are two scores, Lewis score and CECDAI (capsule endoscopy Crohn’s disease activity index). But the Lewis score is not specialized for CD, and neither is yet validated for MH.

Transmural inflammation is a characteristic pathological finding of CD. There is still debate whether MH is a sufficient treatment goal of CD. The initial lesion of CD is an aphthoid lesion in the mucosa of the GI tract. This means that MH is at least a necessary condition. Histological healing or transmural healing may become better ideal treatment goalS in the future [13].

As mentioned above, further investigations are needed to stratify a CD objective monitoring strategy which depends on endoscopy and the other imaging modalities, especially for SB. Although endoscopy is situated as one of the objective examinations, it is well-known that inter- or intra-observer variations exist for the evaluation of endoscopic findings. Therefore, endoscopic assessment is objective monitoring in one sense, but subjective in another sense. In this sense, the development of a more feasible, invariable, and validated endoscopic score is required. There are difficult tasks to be undertaken for the development of a novel endoscopic score for CD, complementary assessment for mucosa, GI tract wall and extrawall information, and different aspects of ulcerative lesion and deformity.