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Constipation is a common functional gastrointestinal disorder [1-3], occurring in approximately 10% of the general population [1], 40% of subjects over 65 years of age [4], in 50-100% of patients with cancer [1] and 11-38% of pregnant women [5]. The prevalence of constipation varies in any given population depending on the evaluative test used, the criteria used to define constipation [6], and depending on whether or not the evaluated population is more likely to self-report the condition. Women, for example, routinely report more constipation than men, and Asians generally report lower rates of constipation [7].
From an etiologic perspective, constipation can be classified as primary constipation (resulting from extrinsic factors such as inadequate privacy or time for defecation, or insufficient fiber intake), secondary constipation (resulting from pathologic changes such as metabolic effects of hypercalcemia) or iatrogenically induced constipation (related to different pharmacologic agents) [8]. Primary constipation can be further differentiated between patients with impaired motility disorders, those with pelvic floor disorders and those with neither [101]. Symptoms of constipation may be overlooked by clinicians who consider it nonlife-threatening compared with the underlying disease [5]. However, opioid-induced constipation (OIC) can adversely affect the patient's quality of life (QoL).
The most common approaches to managing constipation include lifestyle and diet changes, stool softeners, enemas and laxatives. Most patients will respond to such approaches. However, in more complicated cases of constipation, such as OIC, these approaches are often insufficient in that laxatives, for example, will only act on stool consistency but not the underlying cause, such as motor and secretory dysfunction induced by opioids. Opioid use is frequently necessary to treat moderate-to-severe chronic pain and commonly results in OIC; 40-90% of patients taking opioids experience constipation [9].
There are numerous evaluative tests that can be employed to determine the potential cause of constipation of unknown origin. Standard hematological and biochemical profiles are often 'normal'but must be performed in order to detect a potential cause. Colonic transit time can be measured by wireless motility capsule, radio-opaque marker pellets or scintigraphy [10]. Anorectal manometry and balloon expulsion tests are used to evaluate pressure in the anal sphincter muscles, rectal sensitivity and anorectal coordination. Flexible sigmoidoscopy or colonoscopy can assess mucosal lesions. Defecography and MRI testing are used when pelvic...