[Ultrahigh magnifying endoscopy: development of CM double staining for endocytoscopy and its safety]

Endocytoscopy is ultrahigh magnifying endoscopy which enables in vivo cellular imaging of gastrointestinal mucosa. Double staining using both 0.05% crystal violet and 0.1% methylene blue (CM double staining) was developed as this was anticipated to produce similar results to conventional haematoxylin-eosin staining in histology. Endocytoscopy with CM staining enables us to evaluate tissue atypia by approximating the tip of the endoscope onto the mucosal surface. Our initial clinical experience of 152 patients who underwent endocytoscopic examination did not identify any patients with clinically evident side effects. The safety of staining methods has recently been questioned in the literature and in order to clarify this further, a literature review was undertaken. There are only a few reports warning against the use of dye, due to toxicity. This was particularly apparent in animal studies with increased risk of carcinogenesis after one year of daily dye administration. Single administration of dye, however, does not seem to cause severe side effects especially at the low concentrations used during endoscopy. Olliver et al. described one case of genetic injury secondary to dye administration, but carcinogenesis after routine chromoendoscopy has not been verified. Although there is not sufficient evidence to support that genetic injury results in carcinogenesis, we advocate measures during endoscopy to reduce the volume and concentration of dye solution in contact with the gastrointestinal mucosa. Therefore, regularly suctioning and irrigation should be routinely performed as a precautionary measure.