Letters to the Editor 920 A. Parra-Blanco, K. I. Fu, D. Nicolµs-PØrez, A. Z. Gimeno-García, M. Carrillo, E. Quintero: Is acetic acid really effective as a mucolytic agent for magnifying colonoscopy diagnosis? Magnifying colonoscopy can reliably pre- dict histopathologic diagnosis, both for the neoplastic nature of lesions and the estimation of deep submucosal invasion [1]. Magnifying colonoscopy is applied with chromoendoscopy, either with con- trast stains such as indigo carmine, ab- sorption methods (methylene blue, crys- tal violet, cresyl violet), or more recently with digital chromoendoscopy such as the narrow band imaging (NBI) or the Fujinon Intelligent Chromoendoscopy (FICE) [2, 3]. Acetic acid has been used in digestive endoscopy mainly for the study of Barrett’s esophagus [4]. In a study re- cently published in Endoscopy, Togashi et al. [5] compared the accuracy of acetic acid plus indigo carmine either alone or in a combination to predict polyp histolo- gy. Acetic acid works as a mucolytic agent and, if not buffered by mucus, reversibly alters the tertiary structure of nuclear proteins in the epithelium [4]. Mucosal surface opacity is increased, decreasing the visibility of the capillaries and hence producing an increased contrast, with the mucosal surface appearing whitish. In their interesting study, Togashi et al. [5] showed for the first time that acetic acid can be an alternative to indigo car- mine, which is a very helpful tool for the endoscopist but presents several draw- backs, in particular that it is time con- suming; moreover a covering of indigo carmine on the colonic mucosa could pre- vent the detection of other polyps if it could not be effectively removed after its application. Although acetic acid seems to be at least as good as indigo carmine for the examination of the pit patterns, the study did not clarify whether both agents were similar for the correct esti- mation of the polyp margin. We have been using acetic acid for the study of colorectal polyps since we read this study, and have found it to be a very useful and practical agent when com- bined with magnification colonoscopy ± its cleanliness being remarkable (as would be expected for a transparent agent) compared with indigo carmine. However, we would like to make two points. The first point is that we are not sure that the mucolytic effect of acetic acid is really effective, or effective enough to obviate the use of other agents (e. g. Pronase), which are usually used before the application of absorption stains such as crystal violet. We agree that acetic acid certainly enhances mucosal contrast, but probably in many polyps with abun- dant surface mucus (mainly hyperplastic polyps) the image obtained after acetic acid application may enhance the obser- vation of the mucus covering the polyp. The second point we raise is that this per- sistence of mucus, despite the application of acetic acid, might also interfere with the observation of the capillary network during digital chromoendoscopy (NBI or FICE) in hyperplastic polyps, which in most cases are said not to exhibit any dis- tinct vascular pattern. Here we show a case of a 3 mm sessile polyp detected during screening colonos- copy. Histologic diagnosis could not be predicted by conventional observation, but after two applications of 1 % acetic acid plus magnification, a non-neoplastic crypt pattern was observed; no distinct vascular pattern was evident with FICE (l " Fig. 1), which is in keeping with the descriptions of NBI observation of hyper- plastic polyps. Thereafter, 0.5 % indigo carmine was applied, with an unexpected effect of peeling off the mucus layer. Then, a distinct honeycomb vascular pat- tern was observed, tracing the shape of the hyperplastic-type crypt openings (l " Fig. 2). Acetic acid plus magnifying colonoscopy provides clear images for the differential diagnosis of colonic polyps, and it has several potential advantages over indigo carmine. However this case shows that the reported effect of acetic acid on mu- colysis warrants further evaluation, and probably when we observe some polyps (mainly hyperplastic) after the applica- tion of acetic acid, we may still be obser- ving just a more contrasted mucus layer. Competing interests: None DOI: 10.1055/s-2007-966846 Fig. 1 A sessile polyp 3 mm in diameter ob- served with the Fujinon Intelligent Chromoen- doscopy (FICE) filter 4, after having applied acetic acid twice. A Kudo type II, Fujii non- neoplastic crypt pat- tern can be observed. No vascular pattern can be detected. Fig. 2 Indigo carmine was applied after acetic acid. Unexpectedly, the mucus was peeled off. Repeat observation with FICE filter 4 pro- vides a clear image of the honeycomb-type vascular pattern, which strongly suggests a hy- perplastic polyp. Endoscopy 2007; 39 Downloaded by: Universite Laval. Copyrighted material.