Radioisotope determination of regional colonic transit in severe constipation.

Radioisotope determination of regional colonic transit in severe constipation EDITOR,-We were interested to see the article by van der Sijp et al (Gut 1993; 34: 402-8) on a scintigraphic method of colonic transit measurement compared with the conventional radiological method. There are, however, several points that we would like to raise. They have dismissed the method using methacrylate coated capsules as unnecessary and resulting in unpredictable release point. In an early study (30 patients, unpublished data) we examined the colonic transit without the use of pH sensitive capsules and often found overlap of the activity in the small and large bowel in the first day images particularly, if there was slow gastric emptying. Although this is not important in patients with severe chronic constipation , it is a problem when dealing with patients with normal or fast transit (such as some patients with inflammatory bowel disease). The method of methacrylate coating of the capsule, however, is important and in our preliminary studies using capsules with several coatings, there was delayed release in two of 10 patients. As we have modified the method of coating by reducing the number of coatings to two' only in one of 130 patients studied so far has the capsule failed to open before reaching the ascending colon. One should aim for capsule release somewhere in the small intestine , having passed intact through the stomach, as activity tends to collect in the terminal ileum before its release into the colon. In our experience there is no need to obtain release precisely in the terminal ileum. A fundamental problem arises in the use of 'centre of mass' (COM) to describe colonic transit and to compare the two methods of studying transit. COM is useful for examining groups of patients with colonic disorders. The radiologic and scintigraphic methods seem to be no different from each other in this study as only the COM is used to compare groups for both methods. It is of limited value, however, in reporting and treating individual patients, especially when a full range of colonic motility disorders is under study. COM ignores all detailed information obtained by the scinti-graphic method, which is essential for correct classification of different patterns of colonic movement. This is best achieved using para-metric images. A final point is the activity given for these investigations. We have found a four day study sufficient to identify all patterns of …