In cases of hepatic cirrhosis, whatever the cause, the changes in the structure of, and blood flow within, the liver increase the pressure in the portal vein (called portal vein hypertension), which is the vein that drains blood from the bowels to the liver. Portal hypertension induces dilation (opening) of veins within the wall of the oesophagus (food pipe or gullet), which often rupture (break) with severe bleeding. Thus, when liver cirrhosis is diagnosed, an oesophago-gastro-duodenoscopy (OGD) is recommended to detect the presence of oesophageal varices (areas of abnormal dilation of veins). During OGD, a small camera on the end of a tube is inserted down the oesophagus from the mouth. This relays pictures back to a screen. The presence of large varices or of red-coloured signs on even small varices identifies high risk of rupture and bleeding. If high-risk varices are found, treatment with beta-blockers is effective in reducing the risk of bleeding. Capsule endoscopy is a less invasive test than OGD as participants have only to swallow a small device that is able to produce images of the oesophageal walls and could be able to detect the presence of dilated veins.
We searched scientific databases for clinical studies comparing OGD to capsule endoscopy and reporting the size and appearance of varices in children or adults with chronic liver disease or portal vein thrombosis (narrowing of the portal vein). The evidence is current to October 2013.
We found 16 studies assessing the ability of capsule endoscopy to diagnose the presence of varices and grade the risk of bleeding and comparing it with OGD in adults with cirrhosis. Capsule endoscopy, even if more acceptable to participants, cannot replace OGD for the detection of oesophageal varices as about 15% are left undetected and 15% are not confirmed by endoscopy. Even the accuracy in detecting large varices or red marks on varices was very lower than endoscopy. Hence, in conclusion, capsule endoscopy is not sufficiently accurate to replace OGD for the detection of oesophageal varices in cirrhotic participants.
Quality of the evidence
In nine of the sixteen studies there were problems concerning participant selection and incompleteness of reported data which impair accuracy estimates and the transferability of the results.
We cannot support the use of capsule endoscopy as a triage test in adults with cirrhosis, administered before oesophago-gastro-duodenoscopy, despite the low incidence of adverse events and participant reports of being better tolerated. Thus, we cannot conclude that oesophago-gastro-duodenoscopy can be replaced by capsule endoscopy for the detection of oesophageal varices in adults with cirrhosis. We found no data assessing capsule endoscopy in children and in people with portal thrombosis.
Current guidelines recommend performance of oesophago-gastro-duodenoscopy at the time of diagnosis of hepatic cirrhosis to screen for oesophageal varices. These guidelines require people to undergo an unpleasant invasive procedure repeatedly with its attendant risks, despite the fact that half of the people do not have identifiable oesophageal varices 10 years after the initial diagnosis of cirrhosis. Video capsule endoscopy is a non-invasive test proposed as an alternative method for the diagnosis of oesophageal varices.
To determine the diagnostic accuracy of capsule endoscopy for the diagnosis of oesophageal varices in children or adults with chronic liver disease or portal vein thrombosis, irrespective of the aetiology. To investigate the accuracy of capsule endoscopy as triage or replacement of oesophago-gastro-duodenoscopy.
We searched the Cochrane Hepato-Biliary Group Diagnostic Test Accuracy Studies Register (October 2013), MEDLINE (Ovid SP) (1950 to October 2013), EMBASE (Ovid SP) (1980 to October 2013), ACP Journal Club (Ovid SP) (1991 to October 2013), Database of Abstracts of Reviews of Effects (DARE) (Ovid SP) (third quarter), Health Technology Assessment (HTA) (Ovid SP) (third quarter), NHS Economic Evaluation Database (NHSEED) (Ovid SP) (third quarter), and Science Citation Index Expanded (SCI-EXPANDED) (ISI Web of Knowledge) (1955 to October 2013). We applied no language or document type restrictions.
Studies that evaluated the diagnostic accuracy of capsule endoscopy for the diagnosis of oesophageal varices using oesophago-gastro-duodenoscopy as the reference standard in children or adults of any age, with chronic liver disease or portal vein thrombosis.
We followed the available guidelines provided in the Cochrane Handbook for Diagnostic Test of Accuracy Reviews. We calculated the pooled estimates of sensitivity and specificity using the bivariate model due to the absence of a negative correlation in the receiver operating characteristic (ROC) space and of a threshold effect.
The search identified 16 eligible studies, in which only adults with cirrhosis were included. In one study, people with portal thrombosis were also included. We classified most of the studies at high risk of bias for the 'Participants selection' and the 'Flow and timing' domains. One study assessed the accuracy of capsule endoscopy for the diagnosis of large (high-risk) oesophageal varices. In the remaining15 studies that assessed the accuracy of capsule endoscopy for the diagnosis of oesophageal varices of any size in people with cirrhosis, 936 participants were included; the pooled estimate of sensitivity was 84.8% (95% confidence interval (CI) 77.3% to 90.2%) and of specificity 84.3% (95% CI 73.1% to 91.4%). Eight of these studies included people with suspected varices or people with already diagnosed or even treated varices, or both, introducing a selection bias. Seven studies including only people with suspected but unknown varices were at low risk of bias; the pooled estimate of sensitivity was 79.7% (95% CI 73.1% to 85.0%) and of specificity 86.1% (95% CI 64.5% to 95.5%). Six studies assessed the diagnostic accuracy of capsule endoscopy for the diagnosis of large oesophageal varices, associated with a higher risk of bleeding; the pooled sensitivity was 73.7% (95% CI 52.4% to 87.7%) and of specificity 90.5% (95% CI 84.1% to 94.4%). Two studies also evaluated the presence of red marks, which are another marker of high risk of bleeding; the estimates of sensitivity and specificity varied widely. Two studies obtained similar results with the use of a modified device as index test (string capsule). Due to the absence of data, we could not perform all planned subgroup analyses. Interobserver agreement in the interpretation of capsule endoscopy results and any adverse event attributable to capsule endoscopy were poorly assessed and reported. Only four studies evaluated the interobserver agreement in the interpretation of capsule endoscopy results: the concordance was moderate. The participants' preferences for capsule endoscopy or oesophago-gastro-duodenoscopy were reported differently but seemed in favour of capsule endoscopy in nine of 10 studies. In 10 studies, participants reported some minor discomfort on swallowing the capsule. Only one study identified other significant adverse events, including impaction of the capsule due to previously unidentified oesophageal strictures in two participants. No adverse events were reported as a consequence of the reference standard.