The American Gastroenterological Association (AGA) defines obscure GI bleeding as recurrent or persistent iron-deficiency anemia, positive fecal occult blood test, or obscure-overt bleeding (visible bleeding from obscure cause) with no bleeding source found on endoscopy. Most obscure GI bleeding is due to lesions in the esophagus, stomach, and colon; 5% are due to lesions in the small intestine. Causes of obscure bleeding in the small intestine include angiodysplasia (70%–80%), tumor (5%–10%), and other causes (10%–25%) including those related to medication, infections (tuberculosis), Crohn’s disease, Meckel’s diverticulum, Zollinger-Ellison, vasculitis, radiation enteritis, jejunal diverticula, and chronic mesenteric ischemia. In patients over age 60 years, angiodysplasia is the most likely cause of bleeding, while the most likely cause in those under age 50 years is small bowel tumor.
Estimates of the frequency and natural history of obscure GI bleeding, either overt or occult, are not well established. An estimated 3%–5% of cases of GI bleeding arise from small intestinal lesions. While some cases of GI bleeding will resolve with conservative treatment, other cases will persist with recurrent episodes of overt bleeding or ongoing anemia; these cases are considered obscure GI bleeding. GI bleeding may manifest clinically as overtly visible blood in emesis or feces or as occult bleeding, only detected by the observation of iron-deficiency anemia or fecal occult blood testing. Without anemia, further testing beyond upper and lower endoscopy is not warranted. The source of GI bleeding may be identified nonsurgically using a variety of radiological or endoscopic techniques. However, a source for bleeding may remain unclear even after all conventional diagnostic tests (such as upper endoscopy, colonoscopy, oral contrast small bowel radiographic studies, tagged red blood cell scintigraphy, or angiography) have been performed.
Wireless capsule endoscopy is performed using the PillCam™ Given® Diagnostic Imaging System (previously called M2A®), which is a disposable imaging capsule manufactured by Given Imaging, Ltd. The capsule measures 11 millimeters by 30 millimeters and contains video imaging, self-illumination, and image transmission modules, as well as a battery supply that lasts up to eight hours. The indwelling camera takes images at a rate of two frames per second as peristalsis carries the capsule through the gastrointestinal tract. The average transit time from ingestion to evacuation is 24 hours. The capsule sends the images via wireless radio transmission to a receiving recorder device that the patient wears around the waist. This receiving device also contains some localizing antennae sensors that can roughly gauge where the image was taken over the abdomen. Images are then downloaded onto a workstation for viewing and processing.
The device received marketing clearance from the U.S. Food and Drug Administration (FDA) on August 1, 2001, through the 510(k) process. The FDA clearance provides for the capsule's use "along with – not as a replacement for – other endoscopic and radiologic evaluations of the small bowel." The FDA clarified that the "capsule was not studied in the large intestine." On July 1, 2003, a supplemental 510(k) pre-market notification was cleared, and the labeled indications were modified by removing the “adjunctive” use qualification: “the Given® Diagnostic System is intended for visualization of the small bowel mucosa. It may be used as a tool in the detection of abnormalities of the small bowel.”
In November 2004, the device received FDA clearance for the following labeled indication: “the Given® Diagnostic System with the PillCam™ ESO Capsule is intended for the visualization of esophageal mucosa.” A new model was cleared by the FDA in June 2007, the PillCam ES02 Capsule. In September 2007, the FDA cleared the Olympus Capsule Endoscope System through the 510(k) process for “visualization of the small intestine mucosa.” More recent versions of both these systems also incorporate a blood indicator feature to assist with rapid screening of intestinal lesions with bleeding potential.
In the small bowel, the capsule camera has been most frequently proposed as a technique to identify the source of obscure intestinal bleeding, although recently there has been interest in exploring its use in patients with inflammatory bowel disease. Alternative diagnostic techniques include barium studies or small intestinal endoscopy. In the esophagus, the capsule camera has been proposed as a screening technique for Barrett’s esophagus associated with GERD. Evaluation of the esophagus requires limited transit time, and it is estimated that the test takes 20 minutes to perform. Alternative techniques include upper endoscopy.