Defecatory dysfunction is an ill-defined term that encompasses a broad range of symptoms related to infrequent or hard stools and difficult or incomplete evacuation of the rectum. Patients generally lump these together and think of them collectively as symptoms of “constipation;” when healthy young adults were asked what they mean by “constipation,” they referred, in descending order of frequency, to straining, hard stools, “want to but can’t,” infrequent stools, abdominal discomfort, and “haven’t finished.”¹ Unfortunately, the symptoms reported by patients are not a reliable guide to the pathophysiologic basis of their symptoms or the choice of optimal treatment. Consequently, the Rome Foundation² recommended a two-tiered basis for evaluating constipation: Patients are first asked how many of six commonly reported symptoms of constipation they experience at least 25% of the time, and if they endorse two or more of these symptoms and rarely experience diarrhea, they are said to have clinically significant or “functional” constipation (Table 10-1). If patients meet these symptom criteria for functional constipation and fail to respond to a trial of conservative treatment and laxatives, physiologic testing is recommended to further define the pathophysiologic basis of their constipation and to choose an appropriate treatment.

The main causes of functional constipation can be divided into the four categories listed below. As described later in this chapter, there are different treatment indications for each of these:³

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  Slow transit constipation, in which decreased peristaltic motility in the colon causes a delay in transit throughout the colon

  
  
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  Dyssynergic defecation, which is a functional disorder in which the pelvic floor muscles paradoxically contract or fail to relax sufficiently to allow stool passage when the subject strains to defecate

  
  
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  Obstructed defecation, which is a structural disorder in which evacuation is impeded by factors such as rectal prolapse, intussusception, enterocele, or rectocele

  
  
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  Idiopathic constipation, in which both colonic transit and rectal evacuation are within normal limits and the cause of constipation symptoms is unknown. (This accounts for the majority of patients.)

To understand defecatory dysfunction, one must have a general understanding of what constitutes normal bowel habits. This has been somewhat difficult given the pervasiveness of irritable bowel syndrome and gastrointestinal side effects of medications. A recent study has confirmed that the normal frequency of bowel movements is between three stools per day to three stools per week, and normal stool consistency as measured by the Bristol Stool Scale⁴ is between a rating of three (“like a sausage but with cracks on its surface”) and five (“soft blobs with clear cut edges”) (Figure 10-1). Interestingly, even among a “normal” population, some amount of urgency, straining, and incomplete evacuation is acknowledged⁵ and frequency or severity thresholds must be employed to separate patients with constipation requiring treatment from healthy individuals. Constipation is typically defined by physicians as having a bowel movement fewer than three times per week or having hard or lumpy stools as the usual or most common stool type.

Normal defecation is a complex physiologic process that depends on colonic motility, anorectal sensation, and coordination of abdominal and pelvic floor musculature to produce an increase in intraabdominal pressure and relaxation of puborectalis and anal sphincter muscles. Peristaltic motility in the colon propels indigestible food residues toward the rectum, which functions as a reservoir. When the colon moves a bolus of stool into the rectum, the resultant rectal distention should cause a reflex decrease in the anal resting pressure, which is the rectoanal inhibitory reflex. This decrease in pressure allows the contents in the rectum to be sampled by the anoderm to discriminate whether the material is gas, liquid, or solid.

The cerebral cortex uses this afferent information to determine whether it is a socially acceptable time to defecate. If it is not an acceptable time, the external anal sphincter and puborectalis muscles voluntarily contract and the smooth muscle tone of the rectum relaxes to accommodate and delay defecation. Increasing the volume of rectal distention causes a stronger urge to defecate, and at high volumes of rectal distention, the resting tone of the striated pelvic floor muscles is also reflexively inhibited. Voluntary defecation is normally initiated by “straining” in which the abdominal wall is voluntarily contracted and the diaphragm lowered to increase intrarectal pressure. This increase in rectal distention triggers a reflex relaxation of the internal anal sphincter (smooth muscle) and a reflex inhibition of the striated external anal sphincter and puborectalis. In combination, the relaxation of the internal anal sphincter and striated pelvic floor muscles causes rectal pressure to be greater than anal canal pressure and allows stool to pass through. This process—relaxation of the internal and external anal sphincters and puborectalis—can also be initiated by a contraction of the rectum or by the delivery of a large volume of stool from the descending colon into the rectum, but normally this occurs at inconvenient times and is counteracted by voluntary contractions of the striated pelvic floor muscles.^6-8

Constipation can be related to congenital anomalies, primary causes such as irritable bowel syndrome, and a host of secondary causes as outlined by Chatoor and Emmnauel (Table 10-2).⁹ Functional constipation refers to constipation in which an underlying organic cause or irritable bowel syndrome is not found. Given the variety of symptoms, patients may present along with the many possible aggravating factors that can contribute to constipation; the ROME criteria were developed and are used as a standard definition for functional constipation (Table 10-1).¹⁰

Constipation is a common complaint among the general population and should be considered a symptom rather than a disease. Population studies have suggested that up to 20% of people have functional constipation. Prevalence of functional constipation increases with age and women are three times more likely than men to have constipation.^9,11

Slow Transit Constipation

The main pathophysiologic mechanism behind slow transit constipation is a decrease in high-amplitude propagating contractions throughout the colon.¹² The enteric nervous system regulates colonic transit; however, the enteric nervous system receives input from the autonomic nervous system, which also allows for spinal-mediated reflexes and the effects of stress and emotion on colonic motility.⁹ A variety of abnormalities in the enteric nervous system has been described which could account for absent or diminished numbers of high-amplitude contractions, but there is as yet no consensus on the cause or causes of this motor abnormality. Dysmotility can also occur as a secondary phenomenon due to medication side effects (especially anticholinergic drugs) or systemic diseases.

Dyssynergic Defecation

Dyssynergia is a term that refers to inadequate (ie, less than 20%) relaxation of the pelvic floor musculature and anal sphincters or inappropriate contraction of these muscles during attempted defecation. This causes a more acute anorectal angle and increases anal canal pressures, resulting in a functional outlet obstruction. Dyssynergic defecation appears to be a learned or acquired dysfunction because (a) no neurologic or structural defect has been associated with it and (b) it is quickly reversed with biofeedback training (Table 10-3).

Obstructed Defecation

Anatomic abnormalities can also create an outlet obstruction. The distinction between obstructed defecation and dyssynergic defecation is that in obstructed defecation the pelvic floor muscles relax appropriately with straining, but there is a failure of evacuation due to either a physical impediment to evacuation (eg, rectal prolapse or intussusception) or a decrease in propulsive forces in the rectum due to bulging of the rectum into the vagina (eg, rectocele).

The prevalence of evacuation difficulties has been reported in up to 10% of the middle-aged population.⁹ However, evacuation difficulties related to vaginal prolapse are a condition unique to women. Close to one-quarter of women report at least 1 pelvic floor disorder, 2.9% reporting prolapse.¹³ A recent study confirmed that in 2010, there were 28.1 million American women with at least one pelvic floor disorder, 10.6 million with fecal incontinence, and 3.3 million with prolapse.¹⁴ It has been reported that of women seeking urogynecologic care, 3% have a defecatory compliant or fecal incontinence, the most common being incomplete emptying with bowel movements and straining to have a bowel movement.¹⁵

Posterior vaginal wall prolapse has many names based on where the area of weakness in the tissue is and includes rectocele, enterocele, and perineocele. The term ‘rectocele’ refers to herniation of the anterior rectal wall through the posterior vaginal wall; an ‘enterocele’ typically contains small bowel bulging through the posterior cul-de-sac;¹⁷ finally, a ‘perineocele’ refers to weakness of the perineal body or disruption of the perineal body’s attachments to the rectovaginal septum.

These posterior vaginal defects are felt to contribute to defecatory dysfunction by several mechanisms. Stool may become trapped in the rectocele leading to the feeling of incomplete emptying. A rectocele may also increase rectal compliance causing rectal hyposensitivity, which can worsen evacuation difficulties.⁹ Additionally, the normal expulsive forces may be redirected into the weakened area of the rectovaginal septum rather than out through the anus, which can also result in stool retention, excessive straining, and incomplete emptying (Figure 10-2).¹⁸ Although many women have asymptomatic posterior vaginal wall prolapse, among women with symptomatic prolapse, posterior vaginal wall prolapse is seen in over 50% of women who also have anterior and apical defects,¹⁷ and many patients with prolapse experience symptoms of defecatory dysfunction.^16,17 A common complaint among patients with posterior vaginal wall defects is the need to “splint” or provide manual support along the posterior vaginal wall, perineal body, or around the rectum to assist in defecation.

Rectal prolapse, which is the full-thickness, circumferential protrusion of all layers of the rectum through the anal opening,^19,20 is another anatomical abnormality that can result in defecatory dysfunction with constipation, evacuation difficulties, and fecal incontinence (Figure 10-3).²¹ Occult rectal prolapse or intussusception is defined as when there is rectal wall prolapse without protrusion through the anal opening.²⁰ The incidence of rectal prolapse has been reported as 2.5 in 100,000, and it is more common in women and increases with age. Prolapse of the rectum is highly associated with pelvic organ prolapse; studies have reported that up to one-quarter of women with rectal prolapse may have concomitant uterine prolapse and over a third may have anterior vaginal wall prolapse.¹¹

The pathophysiology of rectal prolapse is not entirely understood but several possible risk factors or etiologies have been identified such as an abnormally deep pouch of Douglas, weak pelvic floor and anal sphincter muscles, redundant rectosigmoid, pudendal nerve damage, and lack of normal fixation of the rectum.¹⁹ Patients may present with rectal pain, mucous or bloody discharge, defecatory difficulties, constipation, fecal incontinence, or bulging from the rectum.^16,19,20

Idiopathic or “Normal Transit” Constipation

Although the principal physiologic mechanisms that are believed to account for the symptoms of constipation are the three described above, it must be kept in mind that the majority of patients who come to their physicians requesting treatment of constipation have neither evidence of significantly delayed colonic transit nor difficulty in evacuating simulated stool from their rectum. They are sometimes referred to as having “normal transit” constipation but a better term is idiopathic. The physiologic basis for symptoms of constipation in these patients is not known, but they are presumed to have a milder type of constipation, which is more likely to respond to conservative management or laxatives compared to patients with slow transit constipation, dyssynergic defecation, or obstructed defecation.

The relative incidence of these different types of constipation is not known for the general population because physiologic tests are required to distinguish between them. However, Nyam and colleagues²² have described their findings in a series of 1009 patients with refractory constipation who were referred for possible surgical treatment of slow transit constipation with colectomy. These patients all underwent both transit studies to identify those with slow transit and anorectal manometry to identify those with dyssynergic defecation. Fifty-two patients (5.2%) had delayed transit alone, 22 (2.2%) had evidence of both delayed transit and dyssynergic defecation, 249 (24.7%) had dyssynergic defecation, and the remaining 597 (59.2%) had no quantifiable abnormality and were classified as having normal transit constipation or irritable bowel syndrome. Because these were patients referred to a tertiary medical center for surgical treatment, we can assume that the prevalence of normal transit constipation would be even higher in patients consulting primary care physicians, community urogynecologists, or gastroenterologists.

History and Physical Examination

Investigation into defecatory dysfunction begins with a thorough history and physical examination. Key history items that should be reviewed include the frequency, timing, and consistency of bowel movements; associated symptoms such as abdominal pain, bloating, and excessive straining; the patient’s perception of incomplete emptying; flatal or fecal incontinence, and any digital maneuvers to facilitate bowel movements, including supporting the perineum or vagina (splinting) or digital removal of stool from the rectum. Complaints of alternating diarrhea and constipation as well as relation to food and dietary factors, such as amount of fiber and fluid intake, should be explored. Urinary symptoms and prolapse complaints need to be investigated as these often coexist. Finally, the routine use of laxatives and enemas to assist with bowel movements that the patient uses should also be assessed. A complete medical history and review of all medication both prescribed, over the counter and herbal, are paramount. Surgical history, especially prior pelvic, rectal, and spinal surgery, is necessary.²³ Any history of physical and/or sexual abuse should be ascertained. Age-appropriate screening for colorectal cancer should be reviewed; currently, the American Congress of Obstetrics and Gynecology recommends colorectal cancer screening for average-risk patients to begin at age 50 years. Any red flags including bloody stools, recent onset of constipation or diarrhea, unexplained weight loss, family history of colon cancer, or abdominal pain should trigger further work-up and possible referral to a gastroenterology specialist.

The physical examination should focus on the abdominal and pelvic examination with particular attention to neurologic and musculoskeletal function. A detailed pelvic examination includes neurologic examination for S2 through S4 with a cotton swab test as well as the bulbocavernous reflex and perianal wink. The pelvic organ prolapse quantification examination can be utilized to evaluate for concomitant prolapse, along with an assessment of pelvic floor muscle function and strength. A rectal examination is a necessity in the work-up of defecatory dysfunction, and involves the assessment for internal and external hemorrhoids, rectal prolapse, anal sphincter and puborectalis strength, resting and squeeze tone, evaluation of the rectovaginal septum for posterior vaginal prolapse, enterocele, and perineal body defects.

A basic screening evaluation for dyssynergic defecation can be performed with a digital rectal examination. While the patient is asked to bear down or attempt to push out the examiner’s finger, an assessment of whether the patient appropriately relaxes the muscles versus paradoxically squeezes around the examiner’s finger can be done. If the patient is able to relax anal canal pressure with this maneuver, dyssynergic defecation can likely be excluded. However, in this artificial setting if there is inadequate relaxation or inappropriate contraction, this may be related to patient discomfort or nervousness during the examination and should be confirmed by anorectal manometry. Finally, if there is suspicion for rectal prolapse, the patient may need to be examined sitting on a toilet to reproduce the rectal prolapse.

There are a variety of validated questionnaires available to assess constipation and quality-of-life measures, such as the Wexner constipation score,²⁴ and bowel-related bother with pelvic organ prolapse, such as the Pelvic Floor Distress Inventory subscale of the Colorectal-Anal Distress Inventory.²⁵ These questionnaires are not reliable indicators of the pathophysiologic mechanism for the symptoms of constipation, but they do provide an important baseline against which the success of treatment can be gauged, and they also indicate which symptoms are most bothersome to the patient. In some patients, depending on the history and presentation, it may be reasonable to check a complete blood count and thyroid-stimulating hormone. When a history of physical or sexual abuse is uncovered, the patient should be referred to an appropriate mental health provider.³

Trial of Medical Management

It is important to keep in mind that the symptoms of constipation presented by the patient are not a reliable guide to pathophysiology or treatment, and that approximately two-thirds of patients who consult their physicians for help with managing constipation will not be found to have abnormalities in colonic transit time, pelvic floor relaxation, or mechanical impediment to evacuation. For this reason, the American Gastroenterological Association²⁶, the American College of Gastroenterology²⁷, the American Society of Colorectal Surgeons²⁸, and the Rome Foundation²⁹ all recommend that in the absence of red flags identified in the history or physical examination, the physician should initiate a therapeutic trial of conservative medical management prior to further laboratory investigations. Conservative medical management is described in a later section of this chapter.