Neurological
Clinical approach
History
The evaluation of constipation begins with understanding the patient’s perspective on their altered bowel function and the time course of constipation development. The acute or subacute onset of constipation requires a more aggressive diagnostic approach to exclude structural lesions, including colon neoplasia, stricture, and volvulus. Likewise, weight loss, rectal bleeding, history of inflammatory bowel disease, family history of colorectal neoplasia, or iron deficiency anaemia requires a structural examination to exclude cancer or other aetiology. Additional helpful details in the patient history include the onset of constipation, frequency of bowel movements, sensation of incomplete evacuation, straining to defecate, consistency of the stool, associated abdominal pain, the need for digitation, perineal splinting or unusual postures for defecation to occur, episodes of bowel incontinence, prior abdominal or pelvic surgery, prior abdominal or pelvic radiation therapy, and prior pregnancies. It is also necessary to review current medications and supplements, current and previously used laxatives with their degree of effectiveness, use of enemas, and use of complementary therapies to treat constipation (e.g. high colonics, herbs, teas). Dietary history includes a general survey of calories ingested, fibre intake, and restricted foods. Given the consistent association of constipation with depression and anxiety, a brief psychological assessment is also warranted. In general, the ideal, evidence‐based approach to the diagnostic evaluation of constipation remains to be identified.
Physical examination
The physical examination is directed to identifying underlying medical causes for constipation, excluding faecal impaction, and providing a preliminary assessment of anorectal function. A faecal mass may be palpable on abdominal palpation.
Rectal examination includes inspection of the perineum at rest and with strain. Normal perineal descent during strain is 1–4 cm. No perineal descent suggests a failure of the pelvic floor to relax and allow the passage of stool. Excessive perineal descent, sometimes characterized as a ballooning of the perineum, indicates excess laxity to the pelvic floor musculature and dyssynergic defecation. This finding is most common in multiparous women. The strength of the anal sphincter muscle at rest and with squeeze is assessed. Puborectalis and anal sphincter relaxation during strain provide a measure of proper of the appropriateness of pelvic floor function. Failure of relaxation or very high anal sphincter resting pressure suggests dyssynergic defecation. The presence of weak anal sphincter pressures may place the patient at risk for incontinence during treatment of the constipation.
Rectal prolapse can be associated with difficult evacuation due to blockage of the anal canal with the rectum. These patients usually also described episodes of bowel incontinence. A more severe rectal prolapse can be identified during strain in the left lateral decubitus position. A better way to assess for rectal prolapse is to have the patient strain over a commode. The examiner places a gloved hand below the anus and can feel the rectal prolapse descend and touch the glove. The degree of rectal prolapse can be assessed by visual inspection. The physical examination, including rectal examination, is a necessary part of the evaluation of any constipated patient.
Diagnostic tests
Laboratory tests often recommended in evaluating constipation include a complete blood count; a metabolic panel that includes electrolytes, creatinine, magnesium, and calcium; and thyroid function tests. If malignancy is suspected, the stool should be assessed for the presence of occult blood. The need for a colonic structural examination is dictated by the need for routine colorectal screening and the presence of red‐flag signs such as rectal bleeding, anaemia, unintentional weight loss, or a recent change in bowel habit. Colonoscopy in patients over the age of 80 carries a greater risk of complications, adverse events, and higher morbidity than in younger patients. It is also associated with a higher chance of poor bowel preparation resulting in inadequate imaging and lower completion rates.34 Therefore, colonoscopy should be performed after careful consideration for the risks and benefits to the individual patient.
Many patients with long‐standing constipation and no red‐flag symptoms can undergo a therapeutic trial with fibre or an osmotic laxative, preserving further evaluation for those who fail to respond to simple interventions. Patients with more severe or medication‐unresponsive constipation may benefit from further evaluation, including physiological testing. It is difficult to predict the underlying pathophysiology of chronic constipation by symptoms alone.35 The presence of slow‐transit constipation or dyssynergic defecation may be suspected by a poor response to a trial of supplemental fibre.36
Currently, additional tests include colon transit measurement, colonic manometry, anorectal manometry, balloon expulsion testing, and defecography. Colonic transit measurements may be performed scintigraphically or using radiopaque markers and plain abdominal radiographs. In practice, few centres have scintigraphy readily available. A variety of techniques have been described for measuring colonic transit using radiopaque markers, some providing data on regional colon transit. Since treatments have not yet been identified for treating regional colonic abnormalities, total colon transit measurements suffice. New imaging techniques to measure gastrointestinal transit are emerging, including tracking magnetic capsules or wireless devices and MRI‐based methods offering cross‐sectional imaging and assessing transit.37 A widely used method to measure colon transit time is the five‐day colon transit measurement using radiopaque markers; it is simple to perform and cost‐effective, but the technique does involve radiation exposure. 24 radiopaque markers (Sitzmark) are ingested, and a plain abdominal radiograph is performed 5 days later.38 Transit is considered prolonged when >20% of the markers (five or more) remain (Figure 20.2). Although markers remaining predominantly in the rectum suggest dyssynergic defecation or outlet dysfunction, the distribution pattern of the markers throughout the colon does not reliably differentiate between primary slow‐transit versus colon transit delayed as a result of outlet dysfunction (i.e. dyssynergic defecation). Normal subjects pass more than 80% of markers within 120 hours.38
Figure 20.2 An abdominal radiograph obtained 5 days after ingestion of a capsule containing 24 radiopaque markers (small circles). The presence of >5 markers on day 5 indicates the presence of slow colonic transit. The majority of the markers reside in the rectum, with a few markers scattered in the sigmoid and descending colon.
Dyssynergic defecation is common and refers to physiological difficulty with the rectal evacuation process due to an inability to coordinate the abdominal and pelvic floor muscles. Synonyms include pelvic outlet dysfunction, pelvic floor dysfunction, anismus, and paradoxical puborectalis contraction. Uncommonly, difficult rectal evacuation may be due to an anal stricture, obstructing
