Introduced in the United States a decade ago, capsule endoscopy was the first noninvasive method for visualizing the entire length of the small bowel. Since then, the development of complementary modalities such as CT and MR enterography and deep enteroscopy have further improved imaging of the small intestine. But capsule endoscopy remains the defining disruptive technology, says Jonathan A. Leighton, M.D., of Mayo Clinic in Arizona.
"Capsule endoscopy revolutionized evaluation of the small bowel. Instead of traditional endoscopy, which visualizes 4 or 5 feet of intestine at best, here was a tiny camera, moving through the entire small bowel, taking tens of thousands of images over an eight-hour period."
Of the four available capsule endoscopy systems, two are currently FDA approved for use in the United States. Similar in safety and efficacy, both are used to evaluate suspected small bowel disease that hasn't been diagnosed with colonoscopy or upper endoscopy. Indications include obscure gastrointestinal bleeding, suspected Crohn's disease, celiac disease and small bowel tumors.
In cases of obscure gastrointestinal bleeding, in particular, capsule endoscopy has been invaluable. With yields from 38 to 83 percent, it has permanently changed the way this challenging disorder is evaluated and managed.
In recent years, capsule endoscopy has also proved important for diagnosing Crohn's disease and for assessing the severity and extent of bowel inflammation.
Dr. Leighton points to multiple studies showing that the yield of capsule endoscopy for Crohn's disease ranges from 43 to 71 percent. This is superior to the yield with ileoscopy, push enteroscopy and CT enterography and equivalent to that of double-balloon enteroscopy.
Capsule endoscopy also has a high negative predictive value, with a very low miss rate of 0.5 percent for small bowel ulcerations as compared with 78.7 percent for other modalities.
"This shows that a diagnosis of Crohn's disease can be excluded with a negative capsule endoscopy in most patients referred for evaluation of chronic abdominal pain or diarrhea," Dr. Leighton says. He adds that capsule endoscopy may also prove useful for early detection of postoperative recurrence.
At the same time, he warns that it is important to be aware of the limitations of using capsule endoscopy in patients with suspected or established Crohn's disease, including the inability to distinguish Crohn's from other forms of inflammation and capsule retention, a particular concern in people with advanced disease or known strictures. Using a patency capsule before capsule endoscopy substantially reduces the risk of retention.
Small bowel tumors have traditionally been difficult to diagnose because of the limited visualization associated with standard endoscopy. Frequency of tumor detection with capsule endoscopy is 6 to 12 percent — better than rates with push enteroscopy and small bowel follow-through.
But Dr. Leighton notes that capsule endoscopy can't differentiate between malignant and benign tumors and may have a 19 percent false-negative rate for single-mass lesions. He adds that given the likelihood that capsule endoscopy will become the treatment of choice for diagnosing small bowel tumors, the miss rate needs further investigation.
Also needing more extensive study is the role of capsule endoscopy in the diagnosis and management of celiac disease where results of current studies have been encouraging but somewhat contradictory.
Dr. Leighton points out that for all its paradigm-shifting benefits, capsule endoscopy has definite limitations. It is impossible, for instance, to control the trajectory of the capsule or to localize identified lesions. The procedure also has a rate of incidental findings and an overall false-negative rate of 11 percent.
Most of these problems are addressed by new technologies and techniques currently in clinical trials. Dr. Leighton points to one capsule, not yet in clinical use, that positions the camera on the side of the device, rather than the end. By providing a circumferential view, this may reduce the number of missed lesions.
Other improvements will help control propulsion, improve optics, reduce battery size and create a self-contained unit that eliminates the need for an external data box.
Beyond this, Dr. Leighton foresees a new generation of capsules that will perform biopsies and therapeutics, deliver drugs and evaluate small bowel motility.
"At Mayo Clinic in Arizona, we have performed more than 2,400 capsule studies, and this rapidly evolving technology has profoundly changed our ability to diagnose and treat small bowel disorders. The future is even more exciting," he says.