Collagenous colitis is a form of microscopic colitis which has recently been recognised as an entity of its own, characterised by chronic watery diarrhoea of unknown aetiology. The diagnosis of collagenous colitis relies on histopathological examination of biopsy specimens from colorectal mucosa, which is usually of normal macroscopic appearance. The typical histological feature is diffuse thickening of the subepithelial collagen layer beneath the basement membrane and an unspecific chronic inflammatory infiltrate of the lamina propria.^1–3

Recently, a confocal laser endomicroscope has been developed that is integrated into the distal tip of a conventional video endoscope. This confocal laser microscope (EC-3870CIFK; Pentax, Tokyo, Japan) was designed to enable subsurface imaging of living tissue during ongoing endoscopy and allows confocal microscopy in addition to standard video endoscopy. Images are generated by intravenously administered fluorescein sodium as the fluorescent contrast agent and an argon ion laser integrated into the system that generates an excitation wavelength of 488 nm.^4,5 For the first time, we used …