Review
Advances in Diagnostic Assessment of Fecal Incontinence and Dyssynergic Defecation

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Disorders of the anorectum and pelvic floor affect approximately 25% of the population. Their evaluation and treatment have been hindered by a lack of understanding of underlying mechanism(s) and a working knowledge of the diagnostic advances in this field. A meticulous evaluation of anorectal structure and its function can provide invaluable insights to the practicing gastroenterologist regarding the pathogenic mechanism(s) of these disorders. Also, significant new knowledge has emerged over the past decade that includes the development of newer diagnostic tools such as high-resolution manometry and magnetic resonance defecography as well as a better delineation of the clinical and pathophysiologic subtypes of constipation and incontinence. This article provides an up-to-date review on the role of diagnostic tests in the evaluation of fecal incontinence and constipation with dyssynergic defecation.

Section snippets

Structure of the Anorectum

The rectum is a muscular tube, 12- to 15-cm long, that terminates at the anus. The internal anal sphincter (IAS), the external anal sphincter (EAS), and the anal vascular cushions encircle the anal orifice and together maintain continence at rest whereas the EAS and puborectalis provide the mechanical barrier during voluntary squeeze.2, 3 The puborectalis is a 0.5- to 1.0-cm thick u-shaped muscle that forms a flap-like valve that creates a forward pull and reinforces the anorectal angle (Figure

Fecal Incontinence

Fecal incontinence is the inability to control or involuntary discharge of stool or gas. It affects 8% to 9% of the population, and disproportionately affects middle-aged women and nursing home residents.9, 10, 11 Advancing age, diarrhea, urinary incontinence, and multiple childbirths, particularly vaginal delivery with sphincter tear, are independent risk factors.9, 10, 11 It significantly affects quality of life and consumes substantial health care resources.9, 10, 11

Clinical and Diagnostic Evaluation of Patients With Fecal Incontinence

The evaluation includes a detailed clinical assessment together with the appropriate physiologic and imaging tests of the anorectum that should provide information regarding the severity and impact of the problem and possible etiology.

Investigations of Fecal Incontinence

The first step is to identify if the incontinence is secondary to diarrhea. If so, endoscopic mucosal evaluation, stool tests, and breath tests may be useful.12 Specific and complementary tests that can define the underlying mechanisms include anorectal manometry, anal endosonography, and neurophysiologic tests.12, 18, 19 An evidence-based summary of commonly performed diagnostic tests is shown in Table 1.

Constipation and Dyssynergic Defecation

Constipation is a polysymptomatic, multifactorial disorder that affects 15% to 20% of the population.34 It is more prevalent in women, elderly, non-Caucasians, and subjects with lower socioeconomic status.34 Constipation places a substantial burden on health care resources,35 and affects both quality of life and psychologic function.36 Recently, significant advances have been made regarding the pathophysiology and diagnostic testing.22, 23, 37, 38, 39

Primary constipation is caused by altered

Pathophysiology of Dyssynergic Defecation

Dyssynergia is an acquired behavioral disorder of defecation. In two-thirds of subjects, dyssynergia is a consequence of faulty toilet habit, painful defecation, obstetric or back injury, and brain-gut dysfunction.26, 37 In the remaining subjects, the coordinated process of defecation was perhaps never learned during childhood.37 Dyssynergic subjects show the inability to coordinate the abdominal, rectoanal, and pelvic floor muscles (Figure 1) during defecation.42, 43 In addition, 30% to 50% of

Diagnostic Tests

It is important to obtain a detailed history with particular emphasis on stool habit and consistency. A recent study reaffirmed that stool consistency and not stool frequency correlated with transit time.44 Also, a carefully performed DRE may reveal dyssynergia (sensitivity, 77%).45 Because a patient's recall of stool habit often is inaccurate46 and symptoms do not predict the underlying pathophysiology,37 diagnostic tests are required to facilitate management. The first step is to identify

Conclusions

A practical knowledge of pelvic floor structure and function will enable the gastroenterologist to seek appropriate clues for etiology. Symptom diaries and DRE can provide useful assessment of sphincter pressure, presence of dyssynergia, and fecal impaction. Anorectal manometry with rectal sensory testing is the preferred method for defining the functional weakness of the anal sphincter and for diagnosis of dyssynergia and abnormal rectal sensation. Newer tests such as high-definition manometry

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    Conflicts of interest The author discloses the following: Dr Rao serves on the Advisory Board for SmartPill Corporation and has received research support.

    Funding This work was supported in part by National Institutes of Health grant RO1 DK 57100-05.

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