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We read the article by Rutter et al (Gut 2004;53:256–60) with great interest. They demonstrated that a dye spraying method with indigo carmine successfully detected dysplastic lesions in surveillance colonoscopy for ulcerative colitis (UC), and proved by back to back colonoscopy that such a method is effective. Since 1979, we have carried out a surveillance colonoscopy programme for UC associated cancer in which we successfully detected colitic cancer at an early stage.1 We have routinely used the dye spraying method with indigo carmine, which enables us to recognise subtle mucosal irregularities. Furthermore, we recently introduced magnifying colonoscopy and pit pattern diagnosis for surveillance colonoscopy for UC.2
We agree with Rutter et al that dye spraying can visualise flat dysplastic lesions. By using this method in our series, we also found a flat dysplastic lesion with low grade dysplasia in a patient with a 10 year history of UC. At first, it was impossible to recognise this lesion at pre-dye spray colonoscopy (fig 1A) but after spraying with indigo carmine, the lesion became evident (fig 1B). Magnifying colonoscopy revealed that the lesion had a type IV pit pattern according to Kudo’s classification,3 which corresponded to the neoplastic pattern of Kiesslich’s classification (fig 1B inset).4 Biopsy specimens revealed low grade dysplasia. In this case, magnifying colonoscopy, used together with the dye spraying method, was very effective in detecting flat dysplasia.
As Kiesslich and Neurath remarked in their accompanying commentary (Gut 2004;53:165–7), the difference in dyes used for chromoendoscopy is also of interest. Dye spraying methods can be divided into two types: contrast method and staining method, according to the dyes used. We consider it wise to understand the differences between the two methods. In the contrast method, dyes such as indigo carmine do not stain colonic mucosa but just form pools at grooves, highlighting the contrast of subtle mucosal irregularities. Dyes used in the staining method, however, such as methylene blue or crystal violet, stain the circumferential convex portions, but not grooves. Therefore, images in the contrast and staining methods are quite different, just like those of negative and positive films in photography. In addition, several differences can be noted between these two methods. Firstly, it takes a few minutes for colonic mucosa to be stained in the staining method whereas colonic mucosa can be seen soon after the dye is sprayed in the contrast method. Secondly, the dye can be diluted by colonic fluid or lavage in the contrast method while this is not the case in the staining method. Hence it is easy to intentionally remove dye in the contrast method while it is difficult to do so in the staining method. Therefore, the contrast method should be first tried, and then, if both methods are required, the staining method should follow. Lastly and most importantly, the contrast method offers better contrast (fig 1C) while the staining method provides a better view of glandular openings or pits (fig 1D).
Together with the article by Rutter et al, we would like to reassure readers that the dye spraying method is an indispensable tool in detecting dysplasia in surveillance colonoscopy in UC.