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Invited Reviews

Wireless Capsule Endoscopy: Indications, Limitations, and Future Challenges

El-Matary, Wael

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Journal of Pediatric Gastroenterology and Nutrition: January 2008 - Volume 46 - Issue 1 - p 4-12
doi: 10.1097/01.mpg.0000304447.69305.cc
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Abstract

Evaluation of small bowel pathology has been a major problem, especially when it comes to the management of obscure gastrointestinal bleeding (OGIB), recurrent bleeding with no source identified in the initial evaluation. Evaluation often was unsatisfactory because of the limited ability to visualize small bowel mucosa with the available endoscopic and radiological tools (1,2). In 2001 the Food and Drug Administration approved a wireless video capsule endoscopy (CE) device (Given Imaging, Yoqneam, Israel) (Fig. 1) in adult patients that has since had a significant impact on managing adult patients with OGIB and small bowel diseases (3).

FIG. 1
FIG. 1:
The capsule used for wireless capsule endoscopy.

WHAT IS CAPSULE ENDOSCOPY AND HOW DOES IT WORK?

The capsule itself is a small device that measures 11 mm × 26 mm and weighs 3.7 g (Fig. 1). It contains a complementary metal oxide–semiconductor imaging-chip video camera, 6 white light–emitting diode illumination sources, 2 silver-oxide batteries, and a radio telemetry transmitter. The image filed is 140 degrees and magnification is ×8 (1,2).

Once swallowed, the capsule moves by peristalsis and is excreted in stools. Video images are captured at 2 frames per second and are transmitted by radiofrequency to a sensor array in a belt that the patient wears around his abdomen for the duration of the battery life (8 hours). The recorded images are then downloaded to a workstation (1,4).

The patients should be fasting for 12 hours before swallowing the capsule. They need to clear their bowels the same way that they do for a colonoscopy. The optimal bowel preparation before CE has yet to be determined. Although Given Imaging recommends fasting for 10 hours without bowel purge (5), there is some evidence that using polyethylene glycol (6), sodium picosulfate (7), sodium phosphate (8), or simethicone (9) may give better imaging. However, some have raised the concern that in patients who are having CE for OGIB, preparation fluids may wash away any blood important for localizing a culprit lesion (10). The patients can drink clear liquids 2 hours after ingestion of the capsule and eat a light meal 4 hours after ingestion (5,11).

Before the capsule is swallowed, 8 skin antennas are taped to the skin of the patient's anterior abdominal wall and connected to the hard drive. After 8 hours, the sensor array and data recorder are removed and the recorded digital information is downloaded into the computer. The capsule comes out with the stools, usually within 24 to 48 hours (11). Patients should return the recorder, antennas, and belt, but do not need to return the disposable capsule.

INDICATIONS

Obscure Gastrointestinal Bleeding

This is the most important and natural indication for using the capsule to visualize the small intestine. Several adult studies have examined the diagnostic role of CE in OGIB. The majority of these studies compared the diagnostic yield (DY) of CE to that of push enteroscopy (PE), small bowel follow-through (SBFT) or enteroclysis, intraoperative enteroscopy, small bowel computed tomography or magnetic resonance imaging, and mesenteric angiography after a negative conventional endoscopy (12–27). Table 1 summarizes these studies.

TABLE 1
TABLE 1:
A summary of the studies looking at the diagnostic yield of capsule endoscopy versus other diagnostic modalities in obscure gastrointestinal bleeding

Diagnostic yield for CE in OGIB varied from 55% to 81% (28,29). CE appeared constantly superior to other techniques in diagnosing the source of bleeding. A recent meta-analysis included 14 studies (total number of patients, 396) comparing DY of CE to PE (3). The yield for CE was 63% compared with 28% for PE. The meta-analysis also looked at the studies comparing DY of CE to other diagnostic tools such as small bowel radiography; DY for CE was 67% compared with 8% for the barium study. The meta-analysis also included studies comparing DY of CE to computed tomography enteroclysis, intraoperative enteroscopy, and magnetic resonance enteroclysis (1 study each) (3). In another meta-analysis, the rate difference (the absolute pooled difference in the rate of positive findings) between CE and other modalities in occult gastrointestinal bleeding was 37% (95% confidence interval [CI] 29.6–44.1) (30).

In a unique study, de Leusse et al (31) randomized patients with OGIB to have either PE or CE as a first-line exploratory technique. CE was able to identify the source of bleeding in 20 of 40 patients with OGIB, compared with 9 of 38 patients in the PE group.

The recent development of double-balloon enteroscopy may serve as a feasible gold standard diagnostic comparator. The diagnostic yield of double-balloon enteroscopy in identifying the cause of small bowel bleeding was 78.9% (32). In another recent report, capsule findings were confirmed in 6 of 6 patients who underwent both procedures (28).

The actual clinical relevance and bleeding potential of the lesion diagnosed by CE remains an unresolved issue. Saurin et al (20) showed that CE was able to detect smaller bowel lesions than those detected with PE. Nevertheless, lesions with a high bleeding potential were only 50% to 60% of those visualized with CE.

A recent study looked at the predictive value of CE over a long-term follow-up. The overall positive predictive value of CE increased from 51% to 72% when only clinically relevant lesions were considered, with a negative predictive value of 93%. The diagnostic yield of CE was shown to be higher in those with overt obscure bleeding compared with those with occult bleeding. The diagnostic yield also would be higher the sooner after bleeding that CE is done (19).

In the pediatric population, the data are still limited. A few case reports (33–35) documented the feasibility of CE in patients with OGIB, the youngest of whom was 2.5 years old (35). In a Canadian prospective, comparative self-controlled trial, Sant'Anna et al (36) examined 30 children (ages 10–18 years) with suspected different small bowel pathology. Four children had obscured bleeding and CE identified vascular malformations in 3 of them. Additionally, CE more accurately identified the source of bleeding when compared with angiography.

In a study of similar design, Thomson et al (37) assessed the diagnostic yield of CE in 29 children, (ages 9.4–15.9 years) with suspected small bowel disease and compared it to standard investigations. A possible source of bleeding was identified in all 6 children with OGIB in the study. Urbain et al (38) found relevant lesions in 60% of children with OGIB that were not detectable before using CE.

It is still not clear where to put CE in the diagnostic algorithm in children with OGIB. A flowchart is suggested for investigating children with OGIB (Fig. 2). It is still too early to suggest using double-balloon enteroscopy in children routinely. Push enteroscopy may have the advantage of therapeutic intervention, but there is convincing evidence that CE has a higher DY. Red blood cell radioisotope scan and mesenteric angiography need an active bleeding process with certain minimal blood loss to be diagnostically helpful. Moreover, mesenteric angiography is an invasive procedure that requires a high level of skill.

FIG. 2
FIG. 2:
Algorithm for investigating children with obscure gastrointestinal bleeding. OGIB = obscure gastrointestinal bleeding; EGD = esophagogastroduodenoscopy; CE = capsule endoscopy; PE = push enteroscopy; RBC = red blood cell.

Crohn Disease

Small bowel Crohn disease (CD) could be challenging to diagnose. The use of CE in the diagnosis of small bowel CD has been examined in several studies (23,39–48) looking at the DY of CE compared with other radiological modalities (Table 2). DY varies from 43% to 71%. Furthermore, the management of the disease may vary after examining patients using CE (47).

TABLE 2
TABLE 2:
A summary of the studies looking at the diagnostic yield of capsule endoscopy versus other diagnostic modalities in CD

Bloom et al (49) found a significant difference between CE compared with ileoscopy and SBFT in visualizing pathological changes in proximal ileum (44% vs 0%) and no significant difference between CE and the other 2 modalities when it came to the distal ileum. A recent meta-analysis included 9 studies (250 patients) comparing DY of CE to that of barium radiography (50). The diagnostic yield of CE was 63% compared with 23% for the barium radiography. Four trials, including 114 patients, compared DY of CE to that of ileocolonoscopy (61% vs 46%, respectively). The yield of CE was 69% compared with 30% for computed tomography enterography follow-through/enteroclysis (3 trials, 93 patients). Interestingly, in patients with suspected initial presentation of CD, the subanalysis of DY of CE versus other modalities showed no statistically significant difference. Nevertheless, the difference was statistically significant in the subanalysis examining DY of CE versus other modalities, in favor of CE, in patients with established CD and suspected small bowel recurrence (50). In another meta-analysis, the rate difference (the absolute pooled difference in the rate of positive findings) between CE and other modalities in CD was 45% (95% CI 30.9%–58%) (30). It is interesting to note that the sensitivity of CE in detecting postoperative recurrence of CD within 6 months following surgery in 32 patients was found to be inferior to ileocolonoscopy (51).

The Canadian pediatric trial looked at 20 children with suspected CD. In 50% of these patients, multiple small bowel lesions consistent with the diagnosis of CD were observed using CE. Small bowel CD was ruled out in 8 children (36). On the contrary, all of the patients with suspected small bowel CD who had successful CE studies in the UK trial were found to have lesions consistent with the diagnosis. Barium meal follow-through (BMFT) detected small bowel disease in only 57% of the patients. In 50% of patients with CD, medical management was increased or refined as a result of using CE (37). In another recent pediatric study, CE was able to demonstrate small bowel lesions consistent with CD in 10 children who had normal SBFT studies (52). Urbain et al (38) made a new diagnosis of CD, which was not detected by other diagnostic means, in 6 children.

Most of the studies that examine CE in this context compare CE to SBFT, which is not sensitive in establishing the diagnosis. Moreover, the small number and the heterogeneity of the patients included in these studies makes interpreting the results difficult. Of course, one major disadvantage is the lack of tissue diagnosis. Furthermore, without standardized validated criteria for diagnosing CD using CE, these findings must be interpreted with caution. A scoring index has been proposed to evaluate CD on the basis of CE findings (erythema, edema, nodularity, ulceration, and stenosis) (53). The applicability and utility of this index in distinguishing CD from other small bowel abnormalities needs further validation and clinical correlation (2).

Other concerns about using CE in managing CD include the anxiety that a capsule may become stuck or impacted against a stricture. The estimated incidence of this complication is 2% in 1 large pooled series (54). Interestingly, most capsule impactions are asymptomatic (55). Most recommend that if the capsule examination does not show colonic pictures and the patient does not observe passage of the capsule in stools, a plain abdominal radiograph should be performed approximately 7 days after the examination to check for capsule retention (55). It has been suggested that doing a small bowel contrast study before CE would avoid such a complication. Alternative options may include careful selection of patients, using a retrievable capsule with a thread, using a smaller capsule (which will also be valuable in children), developing better retrieval methods, or using a “patency capsule(55). The patency capsule has been developed (M2A; Given Imaging) as a noninvasive way to detect possible strictures through a patency scanner. This emits a signal that is able to detect a certain tag in the capsule. The capsule disintegrates into small pieces if it becomes impacted (5). The utility of this new capsule, although explored in a limited number of studies, needs to be examined further.

Polyps

The use of CE in screening for polyps in hereditary polyposis syndromes has been suggested and accepted with a good detection rate compared with magnetic resonance imaging and conventional endoscopy (56,57). However, when it comes to surveillance of the ampulla of Vater, endoscopic examination with lateral view remains the gold standard (2).

In children, CE was reported to be of value in this setting (58,59). CE was superior to BMFT in visualizing polyps in 2 patients with Peutz Jeghers polyposis (37) and comparable to other tests (endoscopic and radiological), but detected a greater number of polyps that were missed with the other modalities (37).

Abdominal Pain

Recurrent abdominal pain remains one of the most common causes of referrals to gastroenterologists, especially in pediatrics. The potential role of CE in the work-up of abdominal pain has been explored. Although CE was superior to other diagnostic tools such as endoscopy, colonoscopy, and SBFT in discovering abnormal findings of the small bowel, the significance of these abnormal findings and the causal relation to the abdominal pain were not clear (60). On that basis, the routine use of CE in this context is not recommended. Nevertheless, it may be used if subtle inflammatory or tumor process is suspected to be the cause of the ongoing pain.

One child with abdominal pain was diagnosed with intussusceptions of the upper jejunum using CE (37). In another pediatric series, CE was able to spot relevant findings in 43% of children with chronic or recurrent abdominal pain (38).

Celiac Disease

Although the gold standard in diagnosing celiac disease is small bowel biopsy with the typical histological changes, CE may have a role in those patients with symptoms despite being on a gluten-free diet (61). It also may have a role in those patients with a positive serological screen who decline endoscopy (62). A recent study, using duodenal histology as a gold standard, has reported good sensitivity (87.5%) and specificity (90.9%) for the detection of villous atrophy (63).

Another potential indication is surveillance for long-term complications, especially in those with suspected refractory sprue (64).

Other Indications

Other disorders of the gastrointestinal tract in which CE may have a role in making the diagnosis include surveillance for side effects of nonsteroidal anti-inflammatory drugs, different intestinal tumors (2,11), mucosal lesions in Henoch-Schonlein purpura (34), causes of protein-losing enteropathy (eg, intestinal lymphangiectasia) (37,65), Mechel diverticulum (59,66), rejection of small bowel transplant, and graft-versus-host disease in patients with stem cell transplants (67). A recent study used CE to identify small bowel changes in patients with refractory pouchitis (68). Currently, the diagnostic role of CE is extending beyond the small bowel to other parts of the gastrointestinal tract (69–71).

SAFETY, POTENTIAL PROBLEMS, AND LIMITATIONS

Although there have been a few reported complications of CE, it is generally a safe and well-tolerated procedure in adult practice. In fact, there is some evidence that patients preferred CE to PE (36,37,72).

The worries about obstruction issues were discussed previously, but generally speaking, BMFT should not be a routine procedure before CE because a negative BMFT does not prevent impaction of the capsule (19). Careful selection of patients may be a better approach. Initial CE evaluation studies can be used to exclude all patients with prior abdominal surgery for bowel obstruction. The manufacturer describes suspected obstruction, strictures, or fistulas as a contraindication for using CE (5). Interestingly, in a series of 10 patients who had small bowel resection for bowel obstruction, CE was found to be safe and well-tolerated (73). Nevertheless, in a recent report, 3 cases suffered from acute small bowel obstruction due to capsule impaction. They needed surgical or enteroscopic removal of the capsule, and it was concluded that the risk of bowel obstruction should be included in the informed consent (74).

The recent invention of the patency capsule may prove to be a safe solution for this scenario. It is excreted intact unless it is impacted in a stenosed segment, in which case it will disintegrate within 40 hours through contact with intestinal fluid. The manufacturer recommends using it before using the conventional CE, to exclude strictures (5).

The clearance of the capsule from the stomach to and through the small bowel is variable and could range from 10 to 228 minutes. A delayed gastric emptying may proportionally reduce the recording time of the small bowel (11), given the battery life is about 8 hours. Moreover, transit time may be significantly longer in patients with gastrointestinal bleeding compared with healthy volunteers (7). The use of erythromycin as a prokinetic agent is controversial. It may accelerate gastric emptying (75), but it may delay intestinal transit (11). Tegaserod was shown to shorten intestinal transit time with no effect on gastric emptying (76). Shortening of gastric emptying time may occur with lying on the right side for the first 2 hours of the procedure (77).

In the Canadian pediatric study, all but 1 capsule were excreted within 2 days (range 10–48 hours). In 1 patient with eosinophilic gastroenteropathy, capsule retention due to unsuspected inflammatory stenosis lasted for 10 days, without adverse symptoms. Excretion of the capsule took place after a short course of steroids. Two patients with CD in the study by Thompson et al (37) experienced delayed capsule passage, 66 hours and 4 weeks, respectively. The latter passed the capsule after steroid use and bowel preparation for colonoscopy (36,37). In a recent pediatric series from China, no capsule retention occurred in 16 children (59). The authors reported no significant difference in capsule excretion time, median gastric transit time, and median small bowel transit time between the pediatric group and an adult group of 15 patients, who served as controls (59).

On the other hand, Moy and Levine (52) reported adverse events in the form of delayed passage of the capsule in 9 children (20%) who had CE. Two patients needed endoscopic retrieval of the capsule from the stomach. Two patients with CD developed symptomatic acute small bowel obstruction and needed surgical removal of the capsule and bowel resection. Another patient responded to steroid intake and passed the capsule spontaneously.

Aspiration, swallowing difficulties (considered a contraindication by the manufacturer), and cricopharyngeal impaction are other problems that may be encountered, especially in younger children or even in older children with swallowing problems, when CE is considered. In this scenario, endoscopic placement of the capsule into the duodenum should be done, a procedure that makes CE more invasive (78). Although the Canadian pediatric trial reported no difficulties in swallowing the capsule except for 1 child, who needed more effort to convince (age range of patients 10–18 years) (36), the British study (age range 6–16 years) reported 1 patient with CD who did not complete the study because of inability to swallow the capsule, and 2 patients who had to have endoscopic placement of the capsule in the stomach for the same reason (37). In the Chinese series, 13 of 16 children were able to swallow the capsule and gastroscopy with an overtube was used to deliver the capsule in the remaining 3 children (59).

The other safety issue is using CE in patients with cardiac pacemakers and other electromedical devices. Although a cardiac pacemaker is considered a contraindication for CE by the manufacturer, Leighton et al (79) reported a case series of 5 patients with cardiac pacemakers who had CE for OGIB with no adverse cardiac events. No pacemaker-induced interference on CE images was noted. Nevertheless, a larger sample size is needed before confirming the safety of CE in this context.

Reading time could be considerable, even for experienced staff members (2). In 2002 a consensus panel determined that optimal review rate was 15 images/second, which would therefore require 64 minutes to read a full 8-hour procedure (80). As it is a time-consuming process, a trend toward training other staff members (eg, endoscopy nurses) is likely to help solve this problem (81).

The reliable interpretation of CE images needs considerable experience (having read ≥20 studies) with a high degree of agreement among experienced readers (those who have read ≥50 studies) (82,83). Nevertheless, it is difficult to define the range of normality and, in many occasions, the significance of “abnormal” findings in CE is unknown (84).

Because localizing lesions may be difficult, a software feature aiding in this practice was developed and displayed in the workstation (85,86). Technical problems reported include a poor charge of the battery, resulting in short battery life, and failure of image downloading (37).

One major limitation of CE is the inability to take biopsies or perform any therapeutic procedures. This problem has made double-balloon enteroscopy an appealing option. The latter is a relatively new technique that allows examination of the entire length of the small bowel (87). The sparse data available suggests that the DY of this tool may be comparable with CE, but with the advantage of taking biopsies and performing therapeutic procedures. In a recent study by Li et al (88), CE was even superior to double-balloon enteroscopy in the overall detection rate of small bowel diseases (72% for CE vs 41.2% for double-balloon enteroscopy). However, the latter was shown to be a good complementary technique after initial imaging using CE. Safety and cost-effectiveness analyses comparing this technique to CE are lacking, especially in children.

One final concern about CE, especially in pediatrics, is the cost and source of funding for its use. Interestingly, a simple decision-tree model comparing 2 arms, colonoscopy and SBFT or CE, estimates that CE produces a cost savings of $291 for each case presenting for diagnostic work-up for CD. Sensitivity analysis of varying diagnostic yields of colonoscopy and SBFT versus CE demonstrates that CE is still less costly than SBFT and colonoscopy even at their highest reported yields, as long as the diagnostic yield of CE is 64.1% or better (89).

FUTURE PROSPECTS

There is no doubt that CE is a huge step in the diagnostic work-up of gastroenterology, especially when it comes to small bowel disorders and particularly for OGIB. The growing evidence leads the clinician to explore new routes in using CE. Nevertheless, there are some limitations of which gastroenterologists should be aware, so they may use CE in the most suitable scenarios. No doubt there has been an enormous effort to improve CE technically, and there is a room for more progress (5,90,91). Several innovations have been introduced by the manufacturer since the initial version. Challenges that should be addressed in the near future include increasing the sensitivity and specificity of automatic detection of nonbleeding lesions, prolongation of battery life, obtaining tissue biopsies, managing diffuse bowel diseases, and the introduction of capsule placement and retrieval devices. Recently, a delivery device was used safely and successfully to endoscopically place the capsule in the small bowel in 16 patients ages between 3 and 74 years (92).

The diagnostic role of CE is extending beyond the small bowel. A newly developed capsule that acquires images from both ends (PillCam ESO; Given Imaging) is showing a promising outcome with similar cost-effectiveness in diagnosing some esophageal disorders compared with standard endoscopy (93,94). Nevertheless, some improvement in the technology and learning-curve assessments are still needed to establish more diagnostic accuracy (95,96).

In pediatrics there is certainly a role for CE, especially in children above the age of 10 years. Many centers worldwide are using it in a considerable number of clinical situations (65,97). Based on a 2004 survey of all of the members of the Australian Society of Pediatric Gastroenterology and Nutrition, representing all of the tertiary pediatric gastroenterology units in Australia, it is estimated that CE will be indicated in up to 50 children in Australia each year for investigation of obscure bleeding (98). In a younger age group, CE was used successfully in children as young as 2.5 years old (34). Of course, there will be the problem of swallowing the capsule, which could be solved by endoscopic placement of the capsule into the stomach. This will make CE more invasive in this age group. Recently, the manufacturer has developed accessories specifically designed for the needs of pediatric patients (5). Children can wear a portable belt recorder that enables them to move during the examination. There is some evidence that children prefer this technique to endoscopy (36,37). So far, the published data documenting the use of CE in children are limited and lack proper cost-effectiveness analysis. Proper multicenter, controlled, prospective trials should take place, including a good number of children, and should examine various CE indications, feasibilities, costs, and safety issues.

CONCLUSIONS

Wireless capsule endoscopy is one of the most important recent inventions in the world of gastroenterology, one that has helped in the diagnostic work-up of small bowel diseases, especially in the area of obscure gastrointestinal bleeding. An extended role for CE has grown to include an expanding spectrum of other small bowel pathology, and even other parts of the gastrointestinal tract. More research is needed to explore the utility and feasibility of using CE in these areas.

In pediatric gastroenterology, the role of CE has been explored in small trials. The results, so far, have been promising. On a parallel line, technical improvement and tuning of the capsule also is promising, yet collaborative work needs to be done to identify new prospects for this valuable tool in several pediatric gastrointestinal areas.

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Keywords:

Capsule; Children; Endoscopy

© 2008 Lippincott Williams & Wilkins, Inc.