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Chronic constipation (CC) is a prevalent disorder, which according to recent estimates, has a global prevalence of 14% (95% CI: 12–17%) and is associated with significant cost and health care utilization.[1, 2] Subtypes of CC include normal and slow-transit constipation and dyssynergic defecation (DD), which refers to the paradoxical contraction or inadequate relaxation of the pelvic floor on attempted defecation. As symptoms do not reliably discriminate between subtypes of CC, diagnostic tests are frequently required. Distinguishing patients with DD from other subtypes of CC is important clinically as they may be less likely to respond to traditional medical and dietary therapies and may be more likely to respond to biofeedback therapy.[4-6]
The Rome Criteria require a combination of two abnormal dynamic tests of the pelvic floor on attempted defecation [i.e., impaired evacuation on balloon expulsion or defecography, and inappropriate contraction of the pelvic floor muscles or incomplete relaxation of the anal sphincter on manometry, electromyography (EMG), or imaging) to diagnose DD (Table 1). The clinical utility and application of the Rome Criteria for DD have not been well evaluated and the individual pelvic floor dynamic tests lack rigorous evaluation of their testing characteristics, such as test-retest reliability, validity, accuracy, and clinical utility.[1, 8]
Table 1. Rome 3 diagnostic criteria* for functional defecation disorders
|1. The patient must satisfy diagnostic criteria for functional constipation**|
|2. During repeated attempts to defecate must have at least two of the following:|
|a. Evidence of impaired evacuation, based on balloon expulsion test or imaging|
|b. Inappropriate contraction of the pelvic floor muscles (i.e., anal sphincter or puborectalis) or less than 20% relaxation of basal resting sphincter pressure by manometry, imaging, or EMG|
|c. Inadequate propulsive forces assessed by manometry or imaging|
We conducted a systematic review of studies that included patients with CC, who underwent a variety of pelvic floor function testing to determine the prevalence and potential predictors of abnormal findings.
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In this meta-analysis of 79 studies evaluating 7581 patients with CC, the overall prevalence of any single abnormal dynamic pelvic floor test (i.e., anorectal manometry, defecography, MRI defecography) ranged from 14.9% to 52.9% with a median of 37.2%, and the prevalence for manometry was 47.7% (95% CI 39.5–56.1). The prevalence of an abnormal test tended to be lower in studies that evaluated patients by defecography (23.7–32.6%, using all defecography findings, ranging from the lowest to highest prevalences of specific findings in individual studies). The prevalence of an abnormal test was consistent across specialty and geographic area as well as when restricting to studies using Rome criteria.
The significance of this article lies in the synthesis of a body of data that has been historically difficult to synthesize. The challenges to the interpretation of the published data on the prevalence of DD and the diagnostic utility of available modalities are multiple and include the following: various and changing diagnostic criteria, lack of established testing protocols and definitions of positive results, and the fact that publications describe potentially heterogeneous populations, from surgical and GI practices. These circumstances have led the authors of a prior systematic review on diagnostic tests for DD to not proceed to a formal meta-analysis of data.
As an example of the difficulty in comparing studies in this meta-analysis, three studies reporting the prevalence of DD may have used three separate criteria for positivity, such as ‘failure to open the ARA,’ ‘prominent impression of the PR muscle,’ or ‘paradoxical motion of the PR muscle.’ Furthermore, some studies also required a degree of impaired contrast evacuation in addition to one of the above findings to reach a diagnosis of DD. These apparently smaller details are among the many between-study inconsistencies in positive criteria that account for the variability in the prevalence of DD. This meta-analysis attempted to tease out criteria differences between studies.
In the prior systematic review on this topic, heterogeneity of the studies and settings limited data pooling. While there have been a significant number of studies published since the prior review, there is still too much variability in methodology between the studies to have them pooled solely based on the presence or absence of DD. While this variability in the diagnostic strategies used, populations studied, and criteria used to interpret test results limits the ability to compare the results among studies, especially with regard to the prevalence of the DD, a main strength of this review is the focus on the prevalence of specific findings on these tests. By extracting data and grouping studies by specific findings, we provided pooled estimates of the prevalence of each finding, providing a prevalence map of individual abnormalities of pathophysiological relevance in CC.
We believe that these findings also add to our understanding of the epidemiology and evaluation of constipation, by determining the prevalence of findings associated with DD across time, geographical regions, disease definition, and specialty setting.
Caution should be exerted when attempted to extrapolate results. While we have shown the prevalences according to tests side-by-side (Fig. 2), one must remind the reader that this can only loosely be interpreted as a direct comparison between tests, as the prevalence was estimated in different populations for each test.
Figure 2. Pooled prevalence and 95% CI for specific findings according to test. ARA, anorectal angle; PR, puborectalis; EMG, electromyography; MRI, magnetic resonance imaging.
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The relatively lower prevalence yielded by defecography which was apparent among pooled results (Fig. 2) was also true in the majority of studies (60%) evaluating the same patients with defecography and either manometry or BET. The reason behind the lower prevalence of DD by defecography could relate to the increased detection of structural abnormalities, though the presence of structural abnormalities and DD should not be mutually exclusive by definition.
The clinical utility of the increased sensitivity of defecography for structural abnormalities deserves further investigation, as structural abnormalities may be sequelae of longstanding constipation rather than causes of it, and more importantly, they do not appear to interfere with the success of biofeedback therapy. In one study examining the predictors of response to biofeedback, among 151 patients who underwent defecography, dynamic perineal descent, anterior or posterior rectocoele and intussusception were present in 100, 32, and 15 out of 151 patients, respectively, and none of these findings influenced the success of biofeedback treatment for constipation. Another prospective study of 173 patients undergoing biofeedback therapy for chronic constipation found similarly that structural abnormalities (e.g., rectocele, sigmoidocele, intussusception) coexisting with dyssynergia did not impact the rate of response to therapy, which was 55% based patient report of whether or not symptoms were improved.
There is conflicting evidence regarding whether the presence of dyssynergia predicts a response to biofeedback therapy. One study reported a large difference in outcome based on the presence of PFD, which was defined as dyssynergia on ARM and failure to expel a 50 cc balloon in 5 min, with 76% success in those with PFD and 8% in those without. However, in a study of 100 patients, the 60% with dyssynergia on EMG were not more likely to report improvement in constipation following biofeedback therapy (overall response rate was 57%). Similar results were reported in another study in which 65% of participants had dyssynergia by EMG, and this finding did not affect response to biofeedback therapy, which resulted in improvement in 59% of the 49 patients (63% among those with dyssynergia on EMG and 50% among those without). These conflicting results may be indicative of the value of combining ARM with BET, but also highlight potential discrepancies between ARM and EMG in their reliability as predictive tests for treatment response. These contradictory findings could also be attributed to variable severity of pelvic floor abnormalities and to inconsistencies the criteria used for abnormal test results. For example, in a study of 148 patients, the response to biofeedback was better in patients with ‘partial’ relaxation of the anal canal on ARM than in those with no relaxation (78% vs 51%). It is possible that those with partial relaxation may have been classified as not having dyssynergia in other studies.
This meta-analysis has several limitations. First, as we were interested in the prevalence of positive results for individual tests, studies not reporting data from individual tests were excluded. In some cases, this led to the exclusion of studies reporting the prevalence of DD based on a combination of tests. Because current guidelines recommend a combination of tests in the evaluation of DD, these combined prevalences remain of clinical relevance. Regrettably, of the included studies that did report prevalence based on more than one test (Table 4), there was not enough consistency across these studies to pool their data with meta-analysis methods. A second limitation of this study is that, in spite of our data extraction protocol designed to minimize heterogeneity at multiple levels, there was still likely variability in the performance of tests and interpretation of results. We provided the most exhaustive detail of pooled prevalences according to individual test findings and interpretations, yet we could not entirely abate the impact of such variability on our estimates.
A third limitation is intrinsic to most, if not all tests assessing defecatory mechanisms, which rely on artificial simulation in the lab of a physiological activity which is of the most personal and private in nature. In addition, tests performed in the left-lateral position may not faithfully reflect the dynamics of defecation act, which is naturally performed in the sitting position.
Despite the limitations, this study provides evidence that DD is prevalent across referral specialties and geographical regions. Our results, in context of the existing data on predictors of response to biofeedback, support the use of ARM with BET as an initial investigation for CC. Defecography, US, and EMG may provide more detailed information about the anatomy and physiology of the pelvic floor, but this information should not influence the decision to refer for biofeedback, a therapy that is effective even among unselected populations with constipation.
In conclusion, across testing modalities, geographical regions and specialties, a significant proportion of patients with CC show features of DD on diagnostic testing. This represents a sizable patient population for whom we lack evidence-based guidelines for evaluation and management. There is a need for prospective studies designed to evaluate the utility and cost-effectiveness of different approaches to evaluation and management of constipation as well as to determine predictors of response to biofeedback therapy.