Patency device to test feasibility of capsule endoscopy may falsely reassure

Last Updated: 2018-11-19

By Scott Baltic

NEW YORK (Reuters Health) - A device used to determine in advance whether a capsule endoscope can safely pass through a patient's small bowel can occasionally dissolve before the 30-hour threshold, leading "to false reassurance that capsule endoscopy could be performed safely without risk of retention," UK-based researchers warn.

Premature dissolution of the Agile patency device (Given Imaging, Yoqneam, Israel) occurred in 1.3% of cases in this study.

The device is designed to be the same size and shape (26 x 11 mm) as an M2A capsule endoscope, so in theory if the Agile can pass through the small bowel without being stopped by a stricture, so can the capsule endoscope. The patency device contains a radio-frequency (RF) tag detectable with a handheld scanner wand. In the absence of the tag's signal, it had been assumed that the device had been excreted intact.

"About half the time, when the RF scan is performed 30 hours after swallowing the Agile device, the device has been excreted and there is no RF signal," corresponding author Dr. Mark McAlindon, of the Academic Department of Gastroenterology and Hepatology at Sheffield Teaching Hospitals NHS Trust, Sheffield, U.K., told Reuters Health by e-mail.

"The other half, there is still an RF signal, so the next question is whether the Agile device is in the small bowel, or has it passed into the colon," so a limited CT scan is then done. If the device is intact, he explained, it's easy to recognize as an oblong white object, and if it has passed into the colon, that shows that there is no small bowel stricture.

But if the device has broken down before 30 hours have elapsed, McAlindon said, "the component parts of the device might still be in the body (the collapsed membrane, a bit of barium and the RF tag), but no longer the big white lump."

If the CT films are carefully reviewed, he said, "you could see the tiny" -3 x 13 mm - "RF tag, and (in one of the cases presented) a tiny bit of barium."

"If you don't know what you're looking for, it might be reported as negative (that is, no evidence of Agile device), assumed to have passed, and there is false reassurance that there is no stricture," McAlindon concluded.

"Clinicians need to be aware that the tag may appear smaller than expected if lying obliquely and may be confused for surgical clips, intrauterine devices, clothing or other metallic objects attached to the skin," advised the report, which was released online Oct. 27 in Frontline Gastroenterology.

Among 307 consecutive patients who swallowed an Agile patency device between June 2017 and March 2018, five had a persistent RF signal after the device could not be identified on a scout CT film.

All five patients had successful repeat Agile patency studies and then underwent capsule endoscopy.

As to why a patency device might collapse prematurely, the authors note that the device's body is made of a polyurethane membrane that contains compressed lactose, which is dissolved over time by intestinal enzymes, such as lactase. Both lactase activity and the rate at which lactase transits from the jejunum through the rest of the small bowel are highly variable between individuals.

"The value of this small study is that it describes the small risk of premature dissolution of the device," said McAlindon, "but more importantly, it highlights how this can be recognized, which avoids putting patients at unnecessary risk of subsequent retention of a capsule endoscope."

Dr. Robert Enns, of the University of British Columbia, told Reuters Health by e-mail that because of the range of assessment options in the setting of Crohn's disease, and also because of logistic and cost issues around capsule endoscopy (including misleading results from patency devices), many centers restrict capsule endoscopy to cases of obscure gastrointestinal bleeding.

"There is already some lack of confidence in these (patency) devices, and this adds another layer of concern when using them," explained Enns, who was a co-author of 2017 clinical guidelines for the use of capsule endoscopy.

However, he added, "Even with the limitations, there is still a clear benefit for selected patients who are high risk for capsule retention."

Dr. McAlindon has received financial support from Given Imaging Ltd. The other co-authors declared no competing interests.

SOURCE: https://bit.ly/2DfTr7L

Frontline Gastroenterol 2018.