Introduction
Fecal incontinence is a multifactorial disease.
Anorectal physiology studies play an outstanding role in the evaluation of its etiology and severity, the two main factors that constitute the basis for the cor- rect choice of treatment. However, the prognostic role of clinical factors and anorectal physiological tests in predicting the outcome to either conservative or surgical treatment is questionable.
Conservative Treatment
Biofeedback training, in association with kinesitherapy and electrostimulation, is an effective first-line treat- ment for anal incontinence in patients with no impor- tant sphincteric defect, leading to improvement rates ranging between 50% and 92% in different studies [1]
(65–75% in reviews). Several clinical conditions; phys- iological anorectal tests, especially anal manometry, pundendal nerve terminal motor latency (PNTML), anal sphincter electromyogram (EMG), and transanal ultrasound (US) and different treatment methods have been investigated for their possible prognostic value.
However, their significance is still uncertain due to the wide range of variability in the definition of fecal incontinence, in treatment protocols, and in the defini- tion of a successful outcome; the short duration of the follow-up or the lack of follow-up data are other aspects contributing to the confusion. Patient age, and duration and severity of the fecal incontinence were not found to be predictive of the response; on the con- trary, patient motivation and etiology of the fecal incontinence (postsurgical or traumatic) were found to be associated with outcome [2, 3].
Manometric Parameters
Manometric parameters are the most extensively studied factors. In a group of 28 incontinent patients treated with biofeedback, Sangwan et al. [4] found
that, except for increased cross-sectional asymmetry in the high-pressure zone, which may be a forerunner of an adverse outcome, manometric parameters (resting and squeezing anal canal pressure, pressure volume, sphincter length, sphincter fatigue rate) before biofeedback failed to reveal any statistically significant differences between responders and non- responders. Improvement in continence may be independent of resting and squeezing pressures achieved after biofeedback therapy.
In a retrospective analysis of 145 consecutive patients, Fernandez-Fraga et al. [5] found that response to biofeedback training, performed by means of a manometric technique, was not influenced by basal anal pressures, anal canal length, or squeeze pressures.
The rectoanal inhibitory reflex was normal in all patients. In a prospective study of 30 patients treated with electromyographic-based biofeedback training, Rieger et al. [6] found that pretreatment resting or squeezing pressures were unable to predict therapy results. Chiarioni et al. [7] studied 24 patients with fre- quent solid-stool incontinence; sensory discrimination training and sphincter strengthening training were both provided. Baseline measures that predicted a pos- itive treatment response were lower (closer to normal) sensory threshold (for first sensation and urge to defe- cate), and lower thresholds for the rectoanal inhibitory reflex and for automatic external anal sphincter con- tractions during sensory testing, which were significant predictors of biofeedback response. Neither anal squeeze pressure nor incontinence severity was predic- tive of treatment outcome. Improved rectal sensation, expressed by a decreased threshold to rectal distension volume inducing sphincter contraction during biofeed- back training, was found to be consistently associated with a good outcome in two other studies [2, 8].
Pudendal Nerve Terminal Motor Latencies and Anal Ultra- sound
PNTML and anal US are included in the standard pretreatment evaluation of fecal incontinence
Physiological Parameters Predicting the Outcome of Surgical and Nonsurgical Treatment of Fecal Incontinence
Donato F. Altomare, Marcella Rinaldi
24
patients, but there is conflicting evidence about their predictive value of the outcome after biofeed- back therapy. In a study by Rieger et al. [6] of 30 patients who demonstrated anal sphincter disrup- tion, a positive result to biofeedback training was achieved in six patients with sphincter injury, indi- cating that a sphincter defect does not preclude symptom improvement. Similarly, evidence of pudendal neuropathy using PNTML (7/14) did not preclude symptom improvement (3/7) after biofeed- back therapy.
In agreement with Rieger et al. [6], Leroi et al.
[9] found that improvement may be expected despite an external anal sphincter defect demon- strated at endoanal US. Incontinence severity and the occurrence of pudendal neuropathy, shown by an abnormal PNTML, should be considered poor prognostic factors after biofeedback therapy. This negative impact of pudendal neuropathy on the outcome of biofeedback therapy is confirmed by other authors [2, 3], who found that patients with traumatic or iatrogenic sphincter injury have bet- ter results after biofeedback therapy than do patients with neurogenic fecal incontinence in which both the afferent and efferent pathways are impaired. In the authors’ conclusions, PNTML has an important prognostic role prior to biofeedback therapy, and the latter is not the therapy of choice for fecal incontinence related to pudendal neu- ropathy.
Surgical Treatment
It is very difficult to identify parameters predicting the outcome of surgical therapy for fecal inconti- nence because of the variety of currently available surgical options, which can be subdivided into pro- cedures that repair or strengthen the sphincter mech- anism, and neosphincter construction procedures using autologous tissue or artificial devices. Finally, a technique of sacral root neuromodulation may be performed.
Postanal Repair
Posterior levatorplasty is intended to improve conti- nence by sharpening the anorectal angle while lengthening the anal canal. Early success rates range between 32% and 87%, but in a long-term analysis, it dropped to 33% [10]. The authors found that puden- dal neuropathy was the only predictor of a negative outcome after postanal repair. However, this was not confirmed in a subsequent study by Mavrantonis et al. of the Cleveland Clinic (Florida) [11], in which
neither clinical nor physiological variables were pre- dictive of success.
Sphincteroplasty
Overlapping sphincteroplasty is the operation of choice in patients with an anterior external anal sphincter defect, especially in postobstetric trauma.
Overlapping without excision of the scar tissue, as suggested by Slade et al. [12], significantly improves functional results compared with initial reports. This is the most extensively investigated procedure for treatment of fecal incontinence, and many studies have analyzed the prognostic value of anal physiolo- gy tests. Whereas the absence of a correlation between preoperative manometric, ultrasonograph- ic, and electromyographic parameters and outcome is commonly accepted, many authors have consid- ered the role of pudendal neuropathy, and despite conflicting results, some suggest that it may be pre- dictive of a poor outcome.
Laurberg et al. [13] were the first to demonstrate the correlation between the absence of pudendal neu- ropathy and the success of sphincteroplasty in a group of 19 patients, achieving 80% positive results in those without pudendal neuropathy versus 11% in patients with neuropathy. Similar results were subse- quently published by other authors [14–21]. In par- ticular, Sangwan et al. [19] described good results after sphincteroplasty only in patients in whom both pudendal nerves were normal. The relationship between pudendal nerve condition and repair suc- cess is not universally accepted [22, 23]. In a group of 42 patients, Nikiteas et al. found no correlation between failure and pudendal neuropathy, nor did a manometric preoperative evaluation have a predic- tive value [24]; Rasmussen et al. [25] Young et al.
[26], and Chen et al. confirmed the absence of a rela-
tionship between pudendal nerve status and surgical
procedure success [27]. In their conclusions, Buie et
al. [28] found clinical factors rather than the labora-
tory assessment to be predictive of outcome in a
group of 191 patients who underwent anterior
sphincteroplasty. There was no significant difference
in postoperative continence among patients with
normal, unilaterally abnormal, or bilaterally abnor-
mal pudendal latency. In the authors’ opinion, this
result was due to more than one cause: the first was
that PNTML is able to measure the conduction time
of the fastest remaining nerve fibers but does not
quantify the amount of nerve damage; the second
was that the two pudendal nerves may not provide
symmetric sphincter innervation, and this anatomi-
cal factor may explain the greater deficit caused by
unilateral damage. Furthermore, the clinical rele-
vance of unilateral or bilateral neuropathy is ques- tionable due to the lack of homogeneity in literature definitions of normal ranges of PNTML. In conclu- sion, it is possible that above a certain value, PNTML may be predictive of a negative surgical outcome (Table 1).
Total Pelvic Floor Repair
This procedure is a combination of anterior sphinc- ter plication with levatorplasty and postanal repair.
There are currently few reports on this procedure, which describe only small groups of patients, with no physiological investigations.
Dynamic Graciloplasty
Transposition of the gracilis muscle to replace the anal sphincter was first proposed by Pickrell in 1952 [29]. This procedure was subsequently modified by the introduction of muscle electrostimulation in order to transform an easily fatigued muscle into one fatigue resistant, which led to dynamic graciloplasty.
This is the treatment of choice in patients with end-stage fecal incontinence secondary to trauma, neurological abnormalities, or anorectal malforma- tions for whom conventional surgical procedures have failed or are not expected to be useful. Long- term success rates vary widely–from 50% to 70%–according to the surgical center’s experience and the definition of success. Obstructed defecation, in fact, is a significant problem after dynamic gracilo- plasty, and for this reason, some authors suggest the association of an antegrade colonic enema proce- dure. Identification of prognostic factors for obstructed defecation would be helpful, but on this
topic, the literature is completely silent.
All studies of dynamic graciloplasty report a high incidence of complications, especially due to infec- tion or technical problems; furthermore, this proce- dure is very expensive and technically demanding.
For these reasons, better knowledge of factors pre- dictive of outcome is urgently required to help select the most appropriate candidates.
Korsgen and Keighley noted that poor rectal sen- sation is predictive of a negative outcome due to incomplete evacuation and the need for repeated enema washouts; they suggested that normal rectal sensitivity and compliance have an important role in predicting success after dynamic graciloplasty [30].
Baeten et al. also reported poor results in patients with impaired rectal sensation [31]. In a recent study in patients with an anorectal malformation, Koch et al. suggested that results are worse in such patients than in patients affected by incontinence of different etiologies. In their series, the best results were achieved in patients with a minor anorectal malfor- mation compared with patients with a severe malfor- mation, confirming the predictive value of the rectal sensitivity threshold [32].
Rectal sensitivity and type of malformation are indicated as prognostic factors for outcome. All the above authors believe that no other data obtained from physiological investigations are predictive of the outcome.
Sacral Nerve Modulation
This procedure was first described in 1960 for uri- nary difficulties and was then applied in 1995 by Matzel et al. [33] in patients with functional deficits of the anal sphincter but with no morphological defect. Subsequently, this procedure spread rapidly,
Table 1.Success rate after sphincteroplasty according to the presence or not of pudendal neuropathySuccess rate (%)
Author Year No. patients No neuropathy Neuropathy P value
Laurberg [13] 1988 19 80 11 <0.05
Wexner [14] 1991 16 92 50 n.s.
Engel [22] 1994 55 – – n.s.
Simmang [18] 1994 10 70 20 n.s.
Londono–Schimmer [17] 1994 94 55 30 <0.001
Sitzler [21] 1996 31 67 63 n.s.
Felt–Bersma [23] 1996 18 – – n.s.
Sangwan [19] 1996 15 100 14 <0.005
Gilliland [16] 1998 77 63 10 <0.01
Buie [28] 2001 89 61 71 n.s.
n.s. not significant
and continuous technical improvements were made and indications extended. Recently, good results have been reported in patients with fecal inconti- nence caused by scleroderma, partial spinal cord injury, idiopathic sphincter degeneration, and low anterior resection of the rectum [34, 35]. Current data show that sacral nerve modulation (SNM) is a successful treatment for fecal incontinence, featur- ing a 70–80% success rate and an overall complica- tion (minor) rate of 5–10% in a recent review by Kenefick and Christiansen [36] and Jarrett et al.
[37].
Although real mechanisms of action are still part- ly unknown, pelvic and central nervous system neu- ral pathway integrity is generally believed to be a necessary condition for a positive response. Effec- tiveness of the SNM procedure is preliminarily test- ed by means of a peripheral nerve evaluation (PNE), a simple procedure with minimal morbidity per- formed under local anesthesia that has a high pre- dictive value. The permanent implant is performed only in cases of a positive PNE. To determine the predictive value of the electrophysiological anal tests–usually performed as part of the diagnostic workup–in predicting the clinical outcome of the PNE, we retrospectively studied 82 incontinent patients who underwent PNE after complete assess- ment of their anorectal physiology [38]. Data analy- sis showed that the functional level of the external anal sphincter, expressed by the EMG, can predict PNE outcome with an acceptable positive predictive value and sensitivity. The neurophysiological basis underlying this positive correlation is difficult to interpret because the effects of SNM on the external anal sphincter are not well understood, and some studies [39, 40] do not confirm the effects of SNM on squeezing and anal resting pressures demonstrated by early reports [33]. Furthermore, another recent study in experimental animals demonstrated that external anal sphincter activation is mediated by a cerebral response rather than being a direct effect of electrostimulation [41]. This central nervous system involvement would require an intact afferent and efferent neural pathway, but PNTML provides infor- mation only on the integrity of the efferent (motor) endings of the pudendal nerves. If these are abnor- mal, the EMG is pathological. The low number of patients who have undergone motor-evoked sacral potentials (MEPs) precludes the possibility of an in- depth analysis of this aspect.
On the basis of our results, we concluded that only simple anal sphincter EMG can predict PNE outcome with a good positive predictive value and specificity in patients with fecal incontinence. Other, more expensive, tests such as PNTML and MEPs do not add further prognostic information.
Conclusion
In conclusion, to date the literature does not provide sufficiently consistent data indicating which preop- erative variables may predict a positive or negative outcome of conservative or surgical treatment of fecal incontinence.
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