Low rectal volumes in patients suffering from fecal incontinence: what does it mean?

Authors


Dr L. Siproudhis, Gastroenterology Unit, Pontchaillou Hospital, Rue H. Le Guilloux 35033 Rennes Cedex, France.
E-mail: laurent.siproudhis@chu-rennes.fr

Summary

Background : Rectal perception and adaptation to distension are widely heterogeneous in subjects with faecal incontinence.

Aim : To quantify rectal physiology in patients with incontinence and low maximum rectal volume, according to AGA guidelines on anorectal testing techniques.

Patients and methods : 148 patients (12 men, 136 female) with incontinence to liquid and/or solid stools were investigated. Distending isobaric procedures were carried out using an electronic barostat in order to analyse perception and adaptation of the rectum.

Results : Pain during isovolumic rectal distension at a level of 100 mL or less was experienced in 21 subjects (14.2%). As defined by isobaric distensions, incontinent patients with low MTV had more frequently a hypocompliant rectum (62%) when compared with those with higher MTV (31%, P = 0.046). Perception scores tended to be higher at each step of distending rectal pressure: incontinent patients with low MTV had more frequently a hypersensitive rectum (48%) when compared with those with normal or high MTV (24%, P = 0.035). Only four of 21 incontinent subjects with low MTV had an isolated hypersensitive rectum.

Conclusion : Both sensitivity and compliance are altered in patients with low MTV. A more extensive study of the role of sensory and compliance aspects of subjects with incontinence is warranted.

Introduction

Anal dysfunction classically remains the main culprit in faecal incontinence. However, proximal sensation and adaptation of the rectum to distension probably play an important role in this disease for several reasons. Firstly, external anal sphincter responses to rectal stimulation are crucial in preserving continence and they are closely related to rectal sensory function and rectal compliance.1American Gastroenterological Association recommends to analyse the maximum tolerable volume (MTV), stating: ‘if <100 mL, may have value in indicating the presence of visceral hypersensitivity, poor rectal compliance, or rectal irritability, and thereby influence the direction of therapy’2. Although some studies have shown impaired rectal sensation in faecal incontinence,3–5 others have found either no abnormality6 or enhanced perception.7 Rectal compliance has been shown to be lower in incontinent patients in some4,8 but not other studies.9,10 These apparent discrepancies may be related to methodological problems raised by isovolumic stimulation. Indeed, analysis of perception and compliance of the rectum by isovolumic distension models is inaccurate because these models hypothesize that (a) the rectum can be modelled as a closed cylinder, (b) the rectal size does not influence measured rectal compliance, and (c) the rectum is mechanically passive.11,12 Moreover, relative variations in pressure thresholds for eliciting rectal sensation and rectoanal inhibitory reflex are lower than corresponding threshold volumes.13 Finally, volume is not linearly related to rectal diameter or to balloon pressure because air is compressible and because small variations in bag shape and dimensions may affect the pressure–volume relation. For all these reasons, isobaric stimulation is actually preferable to isovolumic distension to determine rectal perception:14

Aims

According to AGA definitions and recommendations on anorectal testing techniques,2 the present study tended: to clarify the subgroup of subjects suffering from faecal incontinence with a low maximum tolerable volume (MTV < 100 mL), to define the respective parts of both compliance and sensory disturbances using a rectal isobaric distension procedure. Symptoms, past history, associated disorders and anal physiology were recorded with the hypothesis of a special context (clinical and demographic differences). Isobaric distensions allowed a pathogenic approach of rectal physiology in such a circumstance.

Patients and methods

Patients

From November 1999 to October 2002, 148 patients (12 men, 136 female) suffering from fecal incontinence to liquid and/or solid stools were investigated in a single physiology unit in order to facilitate diagnosis and therapeutic options. Mean age was 57.2 years (s.d. ± 13.3 years). All patients were evaluated using a standard questionnaire, physical examination, defecating proctogram and anal manometry, all recorded in a prospective database. Patients were excluded when the following abnormalities were encountered: chronic diarrhea, encopresia or stool impaction, severe constipation, rectal or colonic mucosal changes, psychiatric disorders and surgical past history of the rectum or previous radiation of the pelvis.

Methods

Each patient underwent a standard questionnaire, physical examination, defecating proctogram and anal manometry. The questionnaire focused on main anorectal complaints, surgical and obstetrical past histories. Continence failure within the last month was scored on the basis of the Cleveland score using a 0–20 point scale.15 Endosonography allowed morphological analysis of both internal and external anal sphincters (B & K medical 7 and 10 mHz probe; Bruël Kjaer, Toulouse France). Sphincter lesions were recorded and depth of each sphincter was calculated (mean of three separate measures). Defecography was performed as previously described in order to identify internal procidentia, high grade prolapse, perineal descent, rectocele, enterocele and to analyse rectal emptying.16 Internal procidentia and high grade prolapse were defined by an intra anal or exteriorized intussusception of the rectal wall at strain according to radiological classification.17 Enterocele was defined as a radiological hernia of small bowel into the rectovaginal space as previously described.18 Perineal descent was quantified by the maximal length which separated the upper anal canal site and the pubococcygeal line during defecation.

Anal manometry was performed using a 3-lumen, water-perfused catheter to record mean maximal resting pressures at both the upper and lower parts of the anal canal (Smartlab Computerized Motility System, Solal-Sandhill, Strasbourg, France). The catheter had radially distributed side holes, spaced 0.5 cm apart for the two proximal holes. Each of the three lumens was perfused at a rate of 0.1 mL/min with distilled water by an electrically powered compressed pneumo-hydraulic perfusion system (R3B and PIP4-4, Mui Scientific, Mississauga, ON, Canada). Appropriate location of the catheter within the anal canal was verified by a pull-through manoeuvre and during a voluntary squeeze. Mean squeeze pressure at the lower anal part was obtained during a 30-s duration of a squeezing effort. Rectal perception thresholds were first recorded using an isovolumic distension with balloon air inflation.

An electronic barostat was secondly used to stimulate the rectum and anal manometry was used to evaluate responses at different levels of the anal canal. Distension procedures were performed with a highly compliant polyethylene bag placed within the rectum and connected to an electronic barostat (ABS®, Saint Dié, France) as previously described elsewhere.19 During isobaric distensions of the rectum, rectal and anal pressures were continuously recorded by a computerized motility system (Smartlab Computerized Motility System). Phasic distension was performed by inflating rapidly the bag to successive predetermined ascending levels of pressure (increment: 5 mmHg), each level being maintained 60 s and separated from the next by a 60 s rest period at 0 mmHg. The same pressure limits were fixed during the whole study protocol (6 to 31 mmHg) as previously described in healthy subjects.20, 21

Investigated parameters

  • Maximal rectal pressure and motility index recorded by the manometric device during each plateau pressure in order to analyse the occurrence of rectal contractions.
  • Maximal volume of the rectum recorded at the end of each step of preselected pressure.
  • Volume related to compliance, which is defined by a volume variation in response to an ascending pressure. It represents the difference between the resting state (0 mL) and the measured volume, when the preselected pressure is just reached. Because this is a volume variation over the variation of two levels of pressure, this phase may reflect rectal compliance.
  • Volume related to tone, which is a volume variation in response to a stabilized preselected pressure (maximal volume − initial volume). It describes rectal tone (pressure variation = 0 mmHg) in this phasic isobaric distension model.
  • Sensation intensity, at each pressure step (when rectal pressure was just stabilized), by using a six-point scale ranging from no sensation to pain.22 According to previous studies in healthy subjects, a sensitive rectum was defined by a painful perception (score 5 or 6) at low levels of distending pressure (21 mmHg or less), a hypocompliant rectum was defined by low recording volumes (V < 150 mL) at high levels of distending pressure (31 mmHg).20

Statistical analysis

Quantitative variables were expressed as mean ± s.d. Qualitative variables were expressed as positive values. Distributions of qualitative variables were compared between groups by the chi-squared test; distributions of quantitative parameters were compared between groups by variance analyses and unpaired t-tests. For each type of distension, two-way (group, pressure step) anova analyses were performed on anal and rectal pressures, rectal volumes and perception scores. For each analysis, P-values <0.05 were considered to be statistically significant.

Results

Symptoms

Table 1 summarizes baseline characteristics of the population study. It was mainly women (91%) with a surgical past history of hysterectomy for benign diseases (27%), concomitant dyschezia (36%) and urinary incontinence (49%). The fecal incontinence was severe (Cleveland score between 9 and 20): for one half of the population study. Twenty-one subjects (14.2%) experienced pain during isovolumic rectal distension at a level of 100 mL or less. Patients with such a low MTV did not differ from those with normal or high MTV with respect to sex ratio, parity, occurrence of a neurological disorder, outlet constipation, urinary incontinence, weekly stool frequency, faecal incontinence score and symptom duration before evaluation. However, patients with low MTV exhibited significant lower mean age at inclusion when compared with those with normal or high MTV.

Table 1.  Baseline characteristics of study patients
 Study populationMTV >100 mLMTV ≤100 mLP
  1. Quantitative data are means (s.d.), categorical data are number of patients. Analyses were performed using Student's t-test and the chi-squared test (or the Fisher's exact test when appropriate) for quantitative and categorical data, respectively. MTV means Maximal Tolerable Volume during isovolumic distension of the rectum (normal or high > 100 mL, low ≤ 100 mL).

n14812721 
Age57.2 ± 13.359.0 ± 12.248.4 ± 15.80.0006
Sex ratio M/F12/13611/1161/200.99
Parity2.6 ± 1.52.7 ± 1.52.4 ± 1.30.43
Previous anal surgery343130.41
Previous hysterectomy363240.78
Neurological disease9630.12
Pelvic pain201820.71
Dyschezia544860.47
Digitation251960.23
Urinary incontinence726390.63
Weekly stool frequency (n)12.7 ± 13.012.2 ± 13.515.6 ± 9.70.29
Incontinence score (0–20)11.4 ± 5.511.5 ± 5.510.3 ± 5.70.40
Incontinence duration (months)70.2 ± 91.359.8 ± 86.973.2 ± 93.10.54

Anal Physiology

Table 2 summarizes the functional assessment of the anal canal in the study population. When compared with the anal function of patients with normal or high MTV, anal performance of subjects with low MTV did not show any significant difference except the anal length, which tended to be shorter in the latter group. Occurrence of anal sphincter defects or paradoxical puborectalis contraction during attempted defecation did not differ between groups. Anal pressures at rest and during squeezing effort were similar in patients with high or low MTV.

Table 2.  Anal function as evaluated by anal manometry, defecography and endosonography
 Study populationMTV >100 mLMTV ≤100 mLP
  1. Quantitative data are means (s.d.), categorical data are numbers of patients. Analyses were performed using Student's t-test and the chi-squared test (or the Fisher's exact test when appropriate) for quantitative and categorical data, respectively. MTV means Maximal Tolerable Volume during isovolumic distension of the rectum (normal or high > 100 mL, low ≤ 100 mL).

n14812721 
Anal canal length (mm)22.9 ± 10.223.4 ± 10.118.8 ± 10.50.09
Anal pressure (mmHg)
 Upper part at rest33.4 ± 19.133.8 ± 19.429.7 ± 15.20.35
 Lower part at rest34.1 ± 18.133.8 ± 18.635.1 ± 13.60.75
 Squeezing effort36.4 ± 31.237.5 ± 31.829.9 ± 26.10.30
Internal anal sphincter
 Depth (mm)2.4 ± 0.82.4 ± 0.72.5 ± 0.60.87
 Defect9175160.19
External anal sphincter
 Depth (mm)6.4 ± 1.76.4 ± 3.16.0 ± 2.40.33
 Defect706190.62
Paradoxical puborectalis sling332850.96

Usual physiology of the rectum

Table 3 shows the mean data of measured recordings at the rectal level. During isovolumic distension of the rectum, the recording volumes at three level of perception differed between groups. In addition to the MTV (definition criterion), initial threshold and constant perception volumes were significantly lower in subjects with low MTV when compared with those with normal or high MTV. Proctogram evaluations showed that prevalence of rectocele, enterocele and prolapse did not differ between groups. Perineal descent at rest and during attempted defecation had same magnitude in patients with and without low MTV. Finally, the quality of rectal emptying was similar in both groups.

Table 3.  Rectal function as evaluated by balloon distension manometry, electronic barostat, defecography and endosonography
 Study populationMTV >100 mLMTV ≤100 mLP
  1. Quantitative data are means (s.d.), categorical data are numbers of patients. Analyses were performed using Student's t-test and the chi-squared test (or the Fisher's exact test when appropriate) for quantitative and categorical data, respectively. MTV means Maximal Tolerable Volume during isovolumic distension of the rectum (normal or high > 100 mL, low ≤ 100 mL).

n14812721 
First threshold volume (mL)29.5 ± 20.329.2 ± 23.215.7 ± 6.80.009
Constant perception volume (mL)78.1 ± 50.288.9 ± 51.338.3 ± 12.6<0.0001
MTV (mL)149.8 ± 45.7196.5 ± 61.686.7 ± 14.9<0.0001
Rectocele443860.60
Enterocele111010.73
High grade rectal prolapse675890.65
Perineal descent at rest (mm)60.8 ± 19.161.1 ± 19.059.0 ± 21.10.69
Perineal descent at strain (mm)79.3 ± 20.080.0 ± 19.474.0 ± 24.40.28
Emptying duration (s)34.7 ± 21.135.1 ± 21.531.3 ± 18.10.52
Complete rectal emptying595270.89

Rectal adaptation

The Figure 1 illustrates volume adaptation and perception of the rectum to isobaric distensions. When compared with incontinent group with normal or high MTV, patients with low MTV significantly showed smaller volumes at both ascending (Panel A: −28%; P = 0.01) and stabilized (Panel B: −31%; P = 0.002) pressure steps. In both panels, the difference between groups increased with the level of distending pressure (significant pressure effect, significant group × pressure interaction). The volume variation during constant periods of isobaric distension reached lower levels in the latter group when compared with those of the former group (Panel D: −38%; P = 0.005). In this panel, the difference between groups did not differ according to the level of distending pressure (significant pressure effect, non-significant group × pressure interaction). As defined by isobaric distensions, incontinent patients with low MTV have more frequently hypocompliant rectum (62%; 13/21) when compared with those with higher MTV (31%; 49/127, P = 0.046).

Figure 1.

Rectal volumes and rectal perceptions as a function of rectal pressure during phasic isobaric distensions of the rectum in patients according to their level of MTV. MTV means Maximal Tolerable Volume during isovolumic distension of the rectum (normal or high > 100 mL, low ≤ 100 mL). For each of considered parameters, a significant pressure effect was observed (P < 0.001). Panel A: rectal volumes recorded at the end of ascending pressure variation (volume variation related to compliance). This parameter differed between groups (P = 0.01) and there was a pressure × step interaction (P < 0.0001) (anova repeated measure). Panel B: rectal volumes recorded at the end of each pressure plateau (maximal rectal volume). This parameter differed between groups (P = 0.002) and there was a pressure × step interaction (P < 0.0001) (anova repeated measure). Panel C: rectal perception perceived and quantified by the patient on a six-point likert scale (0 no perception, 5 pain). Level of perception was recorded at the end of each pressure plateau (maximal rectal volume). This parameter tends to differ between groups (P = 0.06) and there was no pressure × step interaction (P = 0.47) (anova repeated measure). Panel D: variation of rectal volumes recorded during each pressure plateau (volume variation related to tone). This parameter differed between groups (P = 0.005) and there was no pressure × step interaction (P = 0.33) (anova repeated measure).

Rectal perception

When compared with incontinent group with normal or high MTV, perception scores tended to be higher (P = 0.06) at each step of distending rectal pressure in the low MTV group (Figure 1, Panel C). In this panel, the difference between groups was usually small and it did not differ according to the level of distending pressure (significant pressure effect, non-significant group × pressure interaction). As defined by isobaric distensions, incontinent patients with low MTV have more frequently a hypersensitive rectum (48%; 10/21) when compared with those with normal or high MTV (24%; 31/127, P = 0.035).

Among incontinent subjects with low MTV, 19% (4/21) had both normal sensation and compliance (vs. 44.1%, 6/127 subjects with normal or high MTV; P = 0.033). Six patients among those with low MTV (28%) and nine of those with normal or high MTV (7%) were both hypocompliant and hypersensitive (P = 0.008). Finally, only four of 21 incontinent subjects with low MTV had an isolated hypersensitive rectum.

Discussion

Rectal perception and adaptation to distension are widely heterogeneous in subjects suffering from fecal incontinence. Methods to assess these parameters are not well standardized and the diagnostic utility of these tests remains unclear. Using recommended isobaric distending procedures, impaired or normal adaptation may be encountered in association with alteration of perception in unselected groups suffering from faecal incontinence. Previous studies showed a possible association between rectal compliance and sensation suggesting that subjects with less compliant rectum had reduced 8, 23 or enhanced rectal sensitivity.8, 24 This feature put into question the interpretation of especially low thresholds to rectal distension as defined by the AGA recommendations.2 In the present study, one-fifth of subjects with low MTV as defined on isovolumic distensions had a normal perception and normal compliance using an isobaric distension procedure. We, therefore, recommend performing isobaric distension analyses to confirm low MTV before planning therapeutic options in these subjects.

The present study tried to identify pathogenesis and characteristics of patients suffering from fecal incontinence with a low MTV. Past medical history, anal physiology and associated functional disorders did not differ from the control group. This will discourage extensive investigations in subjects where low MTV does not reflect any particular structural change of anal sphincters or rectal wall motility.

From a clinical point of view, low MTV reflects a severe impairment of rectal compliance in about two-thirds of subjects: this may be rather related to an impairment of neurological control than deficient viscoelastic properties of the rectal wall. In the present study, reduced adaptation was attributable to both active and passive mechanisms as it was observed during both ascending and stabilized preselected pressures (Figure 1). In fact, endoscopical examination did not show any mucosal lesions and no subjects experienced a past history of radiotherapy. An ageing process or a postmenopausal change of rectal wall remains unlikely as mean age was significantly lower in patients with low MTV when compared with those with normal or high MTV. Using impedance planimetry in patients with acute and chronic spinal cord lesions, a previous study suggested that rectal tone is stimulated by the sacral spinal cord but inhibited by supraspinal centers.25 We could speculate that a severe impairment of rectal compliance might be related to a supraconal disturbance. The present study, however, did not show any increased prevalence of central neurological disorders in subjects suffering from faecal incontinence with a reduced rectal capacity.

Isolated hypersensitivity concerns one-fifth of incontinent subjects with low MTV. This has been considered as a physiological marker of irritable bowel syndrome. As previously highlighted in subjects having irritable bowel syndrome, hypervigilance to rectal stimuli may be defined as a descriptor discomfort used at significant lower distending pressures.26 The tendency to select discomfort in the ascending series may be an anticipation response rather than a sensory discrimination. This phenomenon may illustrate a status of irritable bowel syndrome in these patients in whom aberrant activation of the dorsolateral prefrontal cortex has been shown.27 It is, however, unlikely that such a mechanism may mainly explain a low MTV in our incontinent group as an increased perception to distension (hypersensitive rectum) was rarely an isolated condition in patients with low MTV. In such a situation, sensory biofeedback may be a therapeutic approach despite no evidence actually supporting the relationship between enhanced sensitivity to rectal distension and occurrence of faecal leakage. Moreover, promising therapeutic procedures such as sacral nerve stimulation showed that symptomatic improvement was frequently associated with a significant decrease in perception volumes.28

In conclusion, the results of the present study support a role of both sensory and compliance disturbances in patients with low MTV. Rectal compliance is severely altered in the majority of them and it may influence interpretation of rectal sensation to distension. As previously outlined, a more extensive study of the role of sensory and compliance aspects of subjects suffering from incontinence is warranted.8, 23, 24 From a clinical point of view, extensive investigations in the field of pelvic abnormalities are not mandatory as patients with low MTV do not experience different presentation. However, we therefore recommend performing isobaric distensions to confirm low MTV because one among five incontinent subjects has no rectal dysfunction.

From a therapeutic point of view, the rectum is rarely considered as a pharmaceutical or surgical target to treat faecal incontinence. However, isobaric distensions may help analyse the effect of new procedure on the rectal wall. Thus, sacral nerve stimulation has been shown to modify both sensory and tension of the rectal wall in a recent study.29 Moreover, it is conceivable that patients with abnormal rectal physiology will obtain a greater benefit of such a procedure as rectal wall tension decreases during sacral nerve stimulation.29 Finally, a better recognition of physiological impairment may enlarge the fields of rectal surgery in selected patients suffering from incontinence with low compliant rectum, thus bringing it into a similar perspective than bladder surgery.

Acknowledgements

The authors are grateful to Dr Andrea Manunta for his valuable advice in editing the manuscript. They also wish to acknowledge Hélène Briand, Valérie Bicheler, Pascale Leturcq and Alain Ropert who gave useful technical help.

No external funding was received for this study.

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