Constipation is a subjective complaint — a symptom. Analogous to pornography, constipation is easier to recognize than define. However, most definitions include dissatisfaction with bowel movements, because of infrequent stool frequency, difficulty in stool passage, or sensation of stool retention. Healthy individuals have at least three bowel movements per week.
Why don’t my patients respond to fibre as much as the experts say they should?
Fibre has a salutary effect on multiple aspects of health, but its benefits for constipation have been overstated. Often the abdominal gas caused by fibre is more unpleasant than the constipation itself, especially if large amounts of roughage are ingested. Moreover, fibre helps only mild to moderate constipation, and is usually only of mild to moderate benefit. For example, one gram of wheat bulk increases stool weight by less than 3 gm, so if wheat fibre is the sole source of roughage, > 33 gm needs to be ingested. The aim is to increase stool weight to over 100 gm daily.
How should I prescribe fibre?
Fibre has usually been tried before medical advice is sought for constipation. If it hasn’t, it should be started at 12.5 gm daily, then increased to 25 gm/day one week later, with the hope the resulting gas will resolve over time. Doses of bulk above 30-35 gm/day are likely to lead to intolerable bloating, abdominal distention and flatulence. Busy patients find it easier to add a commercial supplement such as psyllium (Metamucil®) than to alter their diets.
Does it matter what kind of fibre is ingested?
Yes. Although insoluble fibre (wheat bran, brown bread, carrots, celery) increases stool weight more than the soluble variety, (oat bran, psyllium, apples, pears, blueberries, strawberries), it also leads to more abdominal gas. Therefore, insoluble fibre should be suggested if the chief complaint is constipation itself, whereas soluble is preferable for the irritable bowel type of constipation characterized by abdominal bloating.
What should the focus of my clinical evaluation be?
We ask about the duration of time the constipation has been present (the longer, the less need for investigations), associated symptoms (focusing especially on red flags such as rectal bleeding, weight loss), and whether the main problem is insufficient stool production, or straining. Stool shape and size are less helpful to use. We strive to do a rectal exam on all patients.
What tests should I do?
Few. The vast majority of constipation is due to idiopathic colonic dysmotility. Textbooks cite numerous diseases underlying constipation but these are almost always evident and well established before they become associated with constipation and almost never present with constipation as the predominant symptom. Medications are the commonest recognized etiology. We ask for serum TSH, calcium, glucose, hemoglobin and albumin, although there’s no convincing evidence in the literature that the likelihood of an abnormal result is greater than in the general population. In patients over age 50, we also suggest colonoscopy, but more for colorectal cancer screening than to find an underlying cause for the constipation — studies have suggested that the chances of finding a lesion at colonoscopy is no greater than in age-matched controls, when the only presenting symptom is constipation (without rectal bleeding, weight loss, etc.).
How does the classification of constipation help management?
Not very much. Constipation has been classified into three types. Slow transit constipation refers to decreased colonic propulsive motility retarding the movement of stool throughout the colon, characteristically presenting with infrequent defecation, most often afflicting young women. In outlet obstruction (“dsynergic defecation”), there’s improper coordination of the muscles required for defecation, leading to straining at stool, commonly seen in the elderly. Rectal examination is especially important in these patients, searching for structural problems such as rectal prolapse or rectocele, although uncommon. Treatment is similar in both cases, but laxatives are most beneficial in slow transit, whereas enemas (phosphate (Fleet®), glycerin (Microlax®), or bisacodyl (Dulcolax®) sometimes relieve outlet obstruction. The most challenging type of constipation is the normal transit variety, in which the colorectum expels stool apparently normally, but there is a misperception of defecation. These three types of constipation can be objectively differentiated by taking serial x-rays of the abdomen after swallowing radio-opaque markers.
Do you mean that there are people who think they’re constipated when they’re not?
All clinicians know patients who feel constipated, with bloating, gas, abdominal distention and a sensation of stool in the colorectum, even when they have a bowel frequency within the normal range of 3 or more movements per week (usually with the help of laxatives). One explanation is that in these individuals the sensation of fecal retention, which they sense as constipation, is due to disturbed propulsive colon motility (irritable bowel syndrome) and not to retained stool (constipation by some definitions) — the dysmotility causes both reduced stool frequency and abdominal discomfort, but it’s the dysmotility and not the stool retention that’s causing the abdominal symptoms. So, it’s not surprising that in these patients laxatives tend to be of only transient benefit.
How should I treat?
Use an algorithmic approach. Because of its over-all beneficial effects on health, and its naturalistic appeal, we still start with ensuring that dietary fibre is at least 25 gm/day, despite its disappointing results. If this isn’t helpful, we add docusate in high doses (4 tablets of docusate sodium Colace® 100 mg/day) or docusate calcium 240 mg two tablets/day). However, evidence for benefit from these “stool softeners” is admittedly meagre, so if the constipation is severe, we skip these drugs. Our next step is an osmotic laxative, either lactulose (if drug plan coverage is available, starting at 15-30 ml every second day), or preferably the more palatable over-the-counter polyethylene glycol 3350 (Pegalax® Restoralax®, Lax-A-Day®) starting at a dose of 17 gm every second day. We aim for a bowel movement every second day to minimize the inconvenience and side effects of taking these formulations (especially hypernatremia). Ask your patient to double the dose (to lactulose 30-60 ml every second day, polyethylene glycol 34 gm every second day) if there’s no benefit after one week.
The stimulant laxative bisacodyl (Dulcolax®) can be harsh, with the potential to injure the bowel mucosa, presumably explaining its unpopularity over the years. A recent clinical trial, though, has indicated that at doses of 5-10 mg qhs it’s effective and safe, even when taken chronically.
What about encouraging fluids?
Spare your patients the lecture. Stool is made in the colon, separated from the mouth by 800 cm of water-absorbing small intestine. An ocean of fluid needs to be ingested before water reaches the colon, almost all of which will be converted to urine. The normal thirst mechanism ensures sufficient fluid intake to solubilize dietary fibre. There’s no physiological or clinical data supporting the use of fluid to ameliorate constipation.
What if the usual laxatives don’t work?
Prucalopride (Restoran®) is a recently introduced serotonin 5-HT4 agonist that promotes propulsive colonic movements, documented to increase bowel frequency in 75% of patients with severe constipation (a bowel movement less than twice per week). At a dose of 2 mg/day, prucalopride approaches the ideal laxative. It works by gently restoring the underlying colonic dysmotility toward normal, has an impressively low side-effect/drug interaction profile, and its efficacy has been documented to be sustained for over two years (i.e. no tolerance). The most important feature to remember about this drug is that it tends to cause diarrhea, sometimes explosive, the first day it’s taken, so warn your patients to stay at home and not discontinue the drug because of this reaction. With time it may become the first-line laxative of choice.
What about herbal remedies?
Almost all of the natural over-the-counter formulations marketed as laxatives contain senna or, less commonly, other anthracene compounds. Experts have traditionally viewed these compounds despairingly because older reports associated them with tolerance, addiction, worsening constipation over time, and colon mucosal discoloration (melanosis). But more recent studies have indicated that tolerance is minimal, that worsening of the constipation often reflects worsening underlying colonic dysmotility, and that melanosis only rarely means that neuromuscular damage has occurred. So a reasonable approach is to point out these issues, and support their use, (if they’re helping), but suggest switching to another laxative if the dosage needs to be increased (since this may mean that tolerance is developing). We only rarely recommend any of these compounds.
And if all of this doesn’t help?
We suggest taking one of the polyethylene-electrolyte colonic lavage formulation (Klean-Prep®, Coyle®, PegLyte®) marketed for colonoscopy preparation, ingested until rectal returns are clear. If the constipation persists afterward, then we tell patients the problem is not the bowel, but the reaction/response to the bowel, a form of functional bowel disease. This is challenging to treat, but we start by providing large doses of encouragement, reassurance, explanation and support (au gratis). Then we prescribe a medication such as chlordiazepoxide HCl-clidinium bromide (Librax®), if discussion is insufficient. On the other hand, if the colon lavage leads to symptom relief, we encourage repeating as required.
What will the consultant do?
Offer more tests than treatment. In addition to colonoscopy, experts can measure colon transit time to classify the constipation, assess anorectal motility searching for treatable lesions causing outlet obstruction, and perform various tests such as balloon expulsion and defecation proctography to document why defecation is impaired. Characteristically, the medical treatment already being taken is tweaked, and defecation training, anorectal feedback and surgery are considered, albeit only rarely recommended. The most common useful outcome is a discussion with the patient about treatment options, coupled with reassurance. This is why we so strongly support referral to a gastroenterologist talk-doc rather than a do-doc, someone who not only does tests but takes the time to engage with the patient.
Gabor Kandel, MD FRCPC, is a gastroenterologist on staff at St Michael’s Hospital and Associate Professor of Medicine at the University of Toronto, ON.
John Axler, MD CCFP, is a family doctor practicing medicine in Toronto, ON.