Baron JH et al. reported the first validated endoscopic index in 1964 [2]. They studied the variation between observers in describing mucosal appearances in UC, and concluded that interobserver agreement was better reached based on mucosal friability and spontaneous bleeding compared with other descriptors. Based on this finding, classification of endoscopic activity using these two factors is proposed with high interobserver agreement (Table 16.2).

Sutherland et al. established the Disease Activity Index using a quantitative rating scale with four variables including endoscopic mucosal appearance ranging from 0 to 3, which also utilizes friability and spontaneous bleeding [3]. A similar clinical disease activity index was defined by Schroeder et al. [4] for assessing the clinical efficacy of coated oral 5-ASA, with a more detailed description of mucosal appearance. This scoring system (called the Mayo score) is convenient for clinical trials, since it simultaneously reflects the overall clinical status as well as endoscopic mucosal appearance; however, it is of note that this endoscopic subscore itself has not been validated yet. The concept of mucosal healing is often defined as MES 0 and 1, which suggests the favorable long-term outcome (Table 16.3).

The confusion in the indices described above is that they are graded based on multiple different aspects of mucosal appearance, such as vascular pattern, friability, bleeding, and ulceration, which are not always altered in parallel. These different factors may appear at different levels, especially in patients who are responding to therapeutic intervention. Therefore, Rachmilewitz proposed an endoscopic index in which four descriptors are independently taken into account (Table 16.4) [5].

Naganuma et al. developed EAI, consisting of six descriptors so that early improvement of mucosal inflammation can be more sensitively detected [6]. It has been shown that EAI is superior to Matts’ score in differentiating responder and non-responder. Kobayashi et al. reported that decrease in EAI after 2-week intravenous cyclosporine inversely correlates to the first year colectomy, indicating that EAI is useful in stratifying early endoscopic improvement [7]. EAI is shown to have a wider range for severe cases, which may allow optimization of treatment based on severity even among patients graded identically as severe using the previous systems such as Matt’s or MES (Table 16.5).