From small-bowel bleeding to anemia: a wider range of indications for the capsule endoscope?

Capsule endoscopy has changed our approach to the management of patients with obscure gastrointestinal bleeding. Prior to the introduction of capsule endoscopy, the small bowel was traditionally examined by means of small-bowel contrast barium studies, push-enteroscopy, and/or intraoperative enteroscopy, depending on the clinical situation. Each of these investigative modalities has significant limitations, however [1] [2] [3] [4]. Newer radiological methods such as computed tomographic enterography, magnetic resonance enterography, and endoscopic methods, including capsule endoscopy and double-balloon enteroscopy [5], have further enhanced our ability to detect and manage small-bowel lesions.

The role of capsule endoscopy in obscure gastrointestinal bleeding has been studied in several prospective trials. Overall, a high diagnostic yield was observed with capsule endoscopy compared with other imaging modalities. In a recent meta-analysis, Triester et al. [6] reviewed 14 prospective studies (n = 396) comparing capsule endoscopy with push-enteroscopy in obscure gastrointestinal bleeding, and reported a yield of 56 % with capsule endoscopy for clinically significant findings compared with a yield of 26 % with push-enteroscopy (P < 0.00001). Three studies (n = 88) compared the diagnostic yields of capsule endoscopy and small-bowel barium radiography. Once again, a significantly higher yield was reported with capsule endoscopy for clinically significant findings (42 %) compared with the yield with small-bowel barium radiography (6 %; P < 0.00001). Furthermore, a consensus statement from the 2006 International Conference on Capsule Endoscopy (ICCE) recommends capsule endoscopy as the next step after esophagogastroduodenoscopy (EGD) and colonoscopy in the evaluation of patients with obscure gastrointestinal bleeding.

Whereas the role of capsule endoscopy in the evaluation of patients with obscure gastrointestinal bleeding is clearly established, what about the role of capsule endoscopy in patients with iron deficiency anemia (IDA)? IDA develops as a result of an imbalance between iron loss and absorption and is the most common form of anemia worldwide. In the USA, approximately 5 % of menstruating women and 2 % of men have IDA [7]. The most common cause of IDA in men and in postmenopausal women is chronic, occult blood loss [8]. Prior to the introduction of capsule endoscopy into clinical practice, the standard care pathway was to evaluate the gastrointestinal tract with EGD and colonoscopy. In patients with no identifiable source of bleeding, random small-bowel biopsies are recommended to evaluate the patient for celiac disease [9]. Despite standard endoscopic evaluation, however, up to 30 % of patients with IDA remain without a definitive diagnosis of the cause of their anemia, and require further evaluation of the small bowel.

In this issue of the “Endoscopy”, Apostolopoulos et al. [10] report their prospective study results in a cohort of 253 patients with IDA. In 202/253 patients (79.8 %) at least one likely cause of IDA was diagnosed by serological tests, EGD with small-bowel biopsies, and/or ileocolonoscopy. In those patients in whom EGD and colonoscopy were not diagnostic, capsule endoscopy revealed one or more small-bowel lesions thought likely to be causing IDA in 29/51 patients, a diagnostic yield of 56.9 %. There are several important aspects of this study that are worth noting. First, the yield of capsule endoscopy in the investigation of IDA was similar to the yield of capsule endoscopy for investigating patients with obscure gastrointestninal bleeding. This finding is not surprising because, in most cases, IDA occurs as a result of chronic occult blood loss. Furthermore, common causes of obscure gastrointestninal bleeding were also found on capsule endoscopy in the evaluation of IDA in this study. Secondly, six patients with a normal-looking terminal ileum on ileoscopy were found to have small-bowel ulcers on capsule endoscopy that were suggestive of Crohn’s disease. The implication of this finding is that, as in patients with obscure gastrointestninal bleeding who have a negative examination of the terminal ileum, patients with IDA should also be evaluated for Crohn’s disease. Thirdly, the yield of capsule endoscopy in the investigation of IDA was significantly higher than the yield of enteroclysis for this indication (56.9 % for capsule endoscopy vs. 11.8 % for enteroclysis; P < 0.0001). Because enteroclysis has to be performed by a skilled radiologist and also because it is not universally available, its replacement by capsule endoscopy will be a welcome transition. Fourthly, looking at 1-year follow-up outcomes of the patients who had positive findings on capsule endoscopy in this study, only half of them received lesion-targeted treatment. The majority of the patients with unexplained IDA were treated with iron supplements and did not require further invasive procedures.

Persuaded that capsule endoscopy should be performed early in the work-up of patients with IDA, the authors then recommended an algorithm from the 2006 ICCE to define the role of capsule endoscopy in patients with IDA. In a stepwise approach to the evaluation of IDA one should consider capsule endoscopy after a negative work-up, which should include serological tests for celiac sprue, EGD with biopsies, and a colonoscopy.

So, the indications for capsule endoscopy in the small bowel are expanding beyond obscure gastrointestinal bleeding and on to IDA. There is also a growing body of literature regarding the role of capsule endoscopy in Crohn’s disease [11], diarrhea, chronic abdominal pain [12], celiac sprue, and polyposis syndromes. These are all conditions in which additional information can be gleaned from capsule endoscopy of the small bowel. These results are encouraging, but more prospective and outcome studies are needed to define the role of capsule endoscopy.

The way that the capsule has been used to provide useful clinical information in the small bowel, by capturing images and providing a video, is similar to the way it has been used in the esophagus and also how it will soon be used in the colon and the stomach. However, it does not provide the information that a physician can obtain using a conventional endoscope and it does not allow the endoscopist to treat the patient. Can a capsule endoscope perform more like a conventional endoscope? Can it allow the endoscopist to target an area specifically? Will it allow for biopsies? Can we use it to perform therapeutic procedures? Allison et al. [13] designed and tested a capsule endoscope that was equipped with a remotely-controlled propulsion system that was capable of transporting the capsule to a desired location. Using this novel approach it is possible to examine and re-examine a particular lesion in real time and to direct the capsule to a desired location. Using radio-controlled triggering and remote-control capsule manipulation, Swain [14] described a method of obtaining biopsies with a capsule that consisted of an evacuated chamber. Swain also developed a prototype coagulation capsule using the principle of exothermic chemical reaction to generate heat [14]. Research in these areas of tissue targeting, the facility to do biopsies, and the facility to perform therapies such as targeted drug delivery and coagulation therapy will one day transform capsule endoscopy from an optical diagnostic tool to a more useful diagnostic and therapeutic tool.

Apostolopoulos et al. [10] suggest that the indications for capsule endoscopy in small-intestinal diseases should be expanded beyond the investigation of obscure gastointestinal bleeding to the diagnostic work-up of patients with IDA. We agree, and in fact see the promise of further expansion even beyond this.

Competing interests: None.

References

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