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| 번호 | 제목 | 등록일 | 조회수 |
|---|---|---|---|
| 56 | Role of Resting Pressure Gradient in the Investigation of Idiopathic Fecal Incontinence [2002년 5월 DCR] | 2011-11-17 | 3604 |
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Stevan G. Stojkovic, M.R.C.S., Leith Balfour, F.R.C.S., Dermot Burke, F.R.C.S., Ph.D.
From the Department of Surgery, Centre for Digestive Diseases at Leeds General Infirmary, Leeds, West
Yorkshire, United Kingdom PURPOSE: One-third of patients who suffer from idiopathic fecal incontinence are found to have maximum mean resting pressures within the normal range. The objective of this study was to determine whether measuring the gradient of pressure at rest throughout the anal canal is a more sensitive
predictor of incontinence in these patients. METHODS: Anorectal physiology measurements were retrospectively reviewed in patients referred over an 18-month period. Two patient groups were selected for the study: Group 1, continent patients (n = 80); and Group 2, patients with idiopathic fecal incontinence (n = 47). Maximum resting pressures,
vector volumes, and resting pressure gradients were all contrasted, sensitivities and specificities were calculated, and receiver operating characteristic curve analyses were performed. Reproducibility studies were also performed for the calculation of the pressure gradient. RESULTS: Patient demographics were similar in the two groups. The resting pressure gradient, maximum mean resting pressure, and vector volumes were significantly lower in incontinent patients
compared with the normal patients (P = 0.0001, all comparisons). The sensitivity (and specificity) of resting pressure gradient, maximum mean resting pressure, and vector volumes were 89 percent (96 percent), 55 percent (98 percent), and 53 percent (88 percent), respectively. CONCLUSION: The resting pressure gradient is the most accurate in detecting fecal incontinence. The authors conclude that this test is simple, reproducible, and identifies an abnormality in the majority of patients with idiopathic fecal incontinence. Since the advent of anorectal physiology and the more recent introduction of endoanal ultrasonography,
our understanding of the etiology of fecal incontinence has greatly increased. We are now able to classify patients into several categories depending on the results of their investigations as well as their history. Sphincter defects can now be accurately identified with endoanal ultrasonography, and neurogenic disorders can be diagnosed with a combination of pudendal nerve terminal motor latency studies and mucosal electrosensitivity testing. However, there is a group of patients who experience fecal incontinence yet have ultrasonically intact anal sphincters, no anal canal sensitivity abnormality, and no obvious medical cause for their symptoms. In these cases, the incontinence may be described as idiopathic. Current management of these patients is difficult, and the results of both surgical and nonsurgical treatments are unpredictable. 1 It is apparent that if we are to improve the management of these patients, we must first identify and understand the physiologic abnormalities associated with idiopathic fecal incontinence (IFI). Several conditions must be met to ensure continence. These are normal consistency of stool, a normal
sampling reflex, intact innervation and musculature, and intact anal canal sensation. In patients with IFI, the incontinence is usually passive, suggesting an internal anal sphincter (IAS) abnormality.Traditionally, physiologic measurement of the IAS has been by measuring the maximum mean resting pressure (MMRP), a parameter that has good reproducibility. However, up to 50 percent of patients with IFI have a normal MMRP. Although MMRP measurement is of some use in assessing the continence mechanism, its restriction is that it is a two-dimensional assessment of a three-dimensional functional organ. Vector volume gives a three-dimensional perspective of the anal canal, however, it fails to take into account the distribution of sphincter pressure profiles. Vector volume analysis as a means of detecting incontinence has previously shown poor results. A measurement calculating the gradient of pressure across the anal canal would also give a three-dimensional perspective, while taking into account the distribution of pressure profiles. Measuring such a gradient may provide a more accurate picture of IAS function. The objectives of this study were to devise a method for calculating such a gradient, termed the resting pressure gradient (RPG), within the anal canal; to determine whether measuring the RPG can discriminate between patients with IFI and patients who are continent; to determine the ability of RPG to detect incontinence compared with other conventional anal function tests; to determine the intraobserver and interobserver variability in calculating the RPG; and lastly, to determine whether measurement of the RPG adds to our understanding of the continence mechanism.
DISCUSSION
Measurement of the MMRP is currently the best method for assessing IAS function. However, MMRP
measures IAS function at a solitary point within the anal canal. It would seem reasonable that a test that measures pressure throughout the anal canal would give a more accurate assessment of the functional anal canal at rest. Although vector volume analysis aims to do this, we have shown that these measurements are less accurate than MMRP in identifying fecal incontinence. Vector volumes fail to take into account the shape of the vectorgram and indeed it is possible for separate patients with entirely different-shaped vectorgrams to have identical vector volumes. The RPG is a new physiologic parameter that we describe. It not only takes into account mean resting
pressures but also the distance over which these pressure changes occur (from the basal to the maximum). The resultant figure is expressed as a gradient. Our results have shown that the MMRP, vector volume, and RPG are all significantly lower in the
incontinent patient compared with those who are continent. However, a more detailed analysis shows that MMRP and vector volume measurements are associated with a relatively high number of false positives and false negatives. For this reason, ROC curves were constructed and under curve areas were calculated. A ROC curve is a good way of showing the relationship between the sensitivity and the specificity of a test, with a greater area under the curve being associated with a more accurate test with fewer false positives and fewer false negatives. Of the three physiologic parameters compared, RPG has the greatest area under the curve, making it the most sensitive and specific test for fecal incontinence. RPG measurement, in part, relies on a subjective measurement made by the observer (D2), hence reproducibility studies were performed to show the ease of determining D2. Our study of the interobserver and intraobserver variability of RPG measurement gave excellent results, showing that RPG is both simple to calculate and also reproducible.
Three tissues, the IAS, the external anal sphincter, and the anal cushions are responsible for generating
the resting pressure throughout the anal canal. The tissues contribute approximately 65 percent, 20 percent, and 15 percent, respectively. In the continent patient, the IAS is the main contributor and so is likely to be responsible for the gradual rise in pressure to the highest point within the anal canal (MMRP). In contrast, the contribution to the resting pressure from the external anal sphincter and the anal cushions is likely to be more uniform in nature, without any great differences in longitudinal pressure. In the patient with IFI, the resting pressure generated may be predominantly an effect of the external anal sphincter and the anal cushions. Although the pressures generated in such patients may suffice to produce an MMRP within the normal range, the lack of a significant pressure difference would tend to lead to a reduced RPG and hence fecal incontinence. Our study seems to support this theory. Attempts have been made to treat patients with IFI by altering the morphology of the anal canal using purified synthetic bovine collagen. This study showed an improvement in patients’ symptoms, but conventional physiologic assessment failed to show any significant differences in the parameters measured. We therefore plan to measure RPG before and after collagen injection treatment in patients with IFI to determine whether RPG is affected. Because up to 50 percent of patients with IFI have normal conventional investigations, a better understanding of the factors involved in the continence mechanism is required. Our study has introduced the concept of an abnormal pressure gradient across the anal canal as a factor in the pathogenesis of IFI. Calculation of this gradient is both simple and reproducible. Further analysis of the RPG may lead to an increased understanding of the continence mechanism and also facilitate improved physiologic assessment of the patient with fecal incontinence.
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