Diagnosis of Acute Gastrointestinal Graft-versus-Host Disease by Early Endomicroscopic Features of the Small Intestine

Graft-versus-host disease (GvHD) represents a major cause for morbidity and mortality in patients who underwent haematopoietic stem cell transplantation (HSCT) [1]. In the gastrointestinal tract as one of the main target organs of GvHD diagnosis may be difficult because of many similar presenting differential diagnoses, most notable, infections by cytomegalovirus [2]. Experts disagree about the best diagnostic approach for patients suspected of acute gastrointestinal GvHD (aGI-GvHD). There have been many studies supporting the endoscopic evaluation of either the lower [3, 4, 5], the upper [6, 7] or both parts of the GI-tract [8, 9]. In either case, the histological evaluation of biopsy samples serves as standard tool to establish the final diagnosis [10].

Considering the rather bad general condition of patients after HSCT as a limiting factor for endoscopic and histological evaluation, some new approaches have been introduced into the diagnostic manual of aGI-GvHD in order to reduce the amount of invasive examinations. Conventional imaging techniques like magnetic resonance imaging [11], computer tomography [12] and high-resolution ultrasonography with Doppler Imaging [13] reported bowel wall thickening in GvHD patients. But as such findings are only unspecific signs of gastrointestinal pathology, conventional imaging techniques cannot replace endoscopy with biopsies [14]. The same holds for video capsule endoscopy which was indeed found to have a high negative predictive value for the detection of aGI-GvHD, but shares the important shortcoming of missing biopsy samples for histological evaluation [15, 16, 17].

At least this method shifted the focus of interest onto the small bowel. Biopsies deriving from this former neglected GI part had shown a high sensitivity for GvHD-related changes in previous studies [18]. As similar results were seen at the study site, the investigators prospectively compared enteroscopy with biopsies to the present gold standard in the diagnostic aGI-GvHD management, colonoscopy with biopsies. In the context of this investigation the large intestine showed much stronger affection by aGI-GvHD than all other locations, although there was no pair of examinations, in which colonoscopy revealed aGI-GvHD without the presence of such findings at enteroscopy. Quite the opposite, enteroscopy even revealed GvHD related pathologies in one case where the respective colonoscopy remained inconspicuous. Consequently, they postulated that enteroscopic findings may replace the need for colonoscopy [19], wherefore post-HSCT patients could remain without stressful bowel preparation, often limited by their rather bad general condition.

One of the latest developments in the endoscopic management of the gastrointestinal tract is the so called confocal laser endomicroscope (CLE). Confocal microscopy was developed by Marvin Minsky in the late 1950s. Its principle is the microscopic scanning of focal points below the surface of an object. In comparison to conventional light microscopy it uses a special filter system to avoid image overlapping by surrounding tissue. In detail, a light source (normally a laser) is focused by a microscope objective lens to a diffraction limited spot on or inside the object. Light that is scattered, or fluorescence excited (achieved through fluorescein staining, for example) and emitted, at the focus in the sample will partially return back through the optics along the path from which it arrived. A beam-splitter placed into the path reflects the return light towards a detector. The optics will focus the light from the focal point in the specimen to its conjugate focus near the detector (hence the technology is termed "con-focal"). Here a spatial filter ("pinhole") is used to extinguish all light deriving from areas outside the focal point. Light reflections from the focal point itself will be forwarded to the detector which is connected to a computer system that digitalises the optical signal and creates the in vivo histological image [20].

Focusing on its clinical impact, confocal microscopy is the first technique to allow in vivo evaluation of tissue structures beneath their surface. Because of many breakthroughs in miniaturisation (mostly in the 1990s) this technology could be applied for intraluminal use in gastroenterology, integrated into a otherwise standard endoscope. It allows the in vivo histological visualisation of the upper 250 micrometers of all walls within the gastrointestinal tract, additionally to the normal function of white light endoscopy (provided by two separate screens on top of the workstation) [20].