Pelvic Floor and Anorectal Disorders: Pelvic Floor and Anorectal: Chronic Constipation

0:00Welcome to Board Pearls. This is episode one of three of the Pelvic Floor and Anorectal Disorders chapter, in the Colorectal and Pelvic Floor Disorders module. This episode is chronic constipation, from the first visit through the prescription drugs. A man who goes four or five times a week has chronic constipation, and his case shows why stool frequency isn't enough for the diagnosis, how chronic constipation differs from irritable bowel, what the three mechanisms are, which laxatives come first, and what a failed trial means. A woman with weight loss and anemia shows which features mean testing comes before treatment. A woman whose constipation fails standard laxatives shows what each prescription drug acts on, how the doses differ from irritable bowel dosing, and why the next drug switches mechanism after a failure. And a man who fails drug after drug shows when to stop changing drugs and start testing.

0:49Here's the first patient. A thirty-eight-year-old man has had trouble with his bowels for two years. He goes four or five times a week, but he strains with most movements, his stools are hard and lumpy, and he often feels he hasn't finished. He has no real abdominal pain, no bleeding, no weight loss, and no family history of colorectal cancer or inflammatory bowel disease, IBD. He takes amlodipine for blood pressure and a daily calcium supplement. A friend told him that going four times a week means he isn't constipated.

1:20His friend is wrong, because he has chronic constipation despite his normal frequency. Chronic constipation is diagnosed by symptoms, not by frequency alone. Most people who report constipation pass stool more than three times a week and still strain, pass hard stools, feel incomplete evacuation, and depend on manual help. It's a syndrome of impaired colonic propulsion, impaired defecation mechanics, or both, and a single number captures it poorly.

1:49The Rome four criteria are built on that symptom cluster. They require symptoms for the last three months, with onset at least six months earlier, and two or more of these features in more than a quarter of bowel movements: straining; lumpy or hard stools, Bristol type one or two; a sense of incomplete evacuation; a sense of anorectal obstruction or blockage; manual maneuvers such as digital evacuation, perineal support, or splinting; and fewer than three spontaneous bowel movements a week. Loose stools should rarely occur without laxatives. Infrequency is only one of six features, so normal frequency doesn't rule the diagnosis out. He has had straining, hard stools, and incomplete evacuation for two years, which meets the criteria.

2:31His lack of pain matters, because it separates chronic constipation from irritable bowel syndrome with constipation. The criteria for chronic constipation require that irritable bowel criteria aren't met. When abdominal pain drives the picture, the diagnosis is irritable bowel with constipation, which shares several drugs with chronic constipation but at different doses and approvals. He has no real pain, so his diagnosis is chronic constipation.

2:59The diagnosis made, the next question is which mechanism he has, because the mechanism decides the next test and the drug class. Normal-transit constipation is the most common, about sixty percent of patients referred to specialty care. The symptoms are present, but colonic transit is normal on testing. Defecatory disorders are next in frequency. They're mostly dyssynergic defecation, in which the puborectalis and external anal sphincter fail to relax during the abdominal push. Slow-transit constipation is the least common, with delayed transit on testing, infrequent movements, often once a week or less, and a reduced response to fiber and stimulants.

3:37The three mechanisms often overlap, so one doesn't exclude another. Years of retained stool from dyssynergia can cause secondary slow transit. And years of straining from primary slow transit can cause secondary defecation problems.

3:52His history and exam give the first clues to his mechanism. Splinting, perineal pressure, or digital evacuation lean toward a defecatory disorder. Stools once a week or less with little response to fiber lean toward slow transit. A digital rectal exam with a simulated push costs nothing, and a sphincter that tightens instead of relaxing when he bears down is the bedside clue to dyssynergia. His relaxes normally.

4:18His history doesn't settle the mechanism, but he doesn't need testing yet. Without alarm features, treatment is empiric first, because most patients with normal or slow transit respond, and testing has poor yield and real cost without red flags. The alarm features reverse the order. They're new symptoms after age fifty, unintentional weight loss, rectal bleeding or iron deficiency anemia, a family history of colorectal cancer or IBD, fever, severe progressive symptoms, and a colonoscopy not done at the age-appropriate interval. He's thirty-eight, with two stable years and no alarm features, so he's treated first.

4:56His treatment starts with education. That covers the normal range of bowel frequency, his worry about laxative dependence, and trying to defecate after meals to use the gastrocolic response. Then comes soluble fiber, introduced gradually toward twenty-five to thirty grams a day. Psyllium is preferred over insoluble bran, which tends to worsen bloating and has a less favorable effect on stool consistency when irritable bowel overlaps. A sudden jump in fiber is a common reason patients quit, which is why it's raised slowly. Adequate fluid and regular physical activity round out the lifestyle steps.

5:31His medication list is reviewed next, because two of his drugs could be causing his symptoms. Opioids, anticholinergics, calcium channel blockers, iron, calcium supplements, and ondansetron are all constipating. His amlodipine is a calcium channel blocker, so it's switched to a non-constipating antihypertensive, and the calcium supplement is stopped.

5:53If those steps aren't enough, laxatives come in order. Polyethylene glycol, seventeen grams daily titrated to effect, is the first-line osmotic laxative. Lactulose and magnesium salts are alternatives, but magnesium is limited in renal impairment because it can cause hypermagnesemia. Stimulants are added when an osmotic laxative isn't enough: bisacodyl five to ten milligrams, or senna eight point six to seventeen point two milligrams.

6:21Stimulants are safe to keep using, despite what patients often fear. The older teaching that chronic stimulant use causes cathartic colon, structural damage to the colon's myenteric nerve plexus, isn't supported by current evidence. Chronic stimulant use is acceptable when symptoms require it. He starts psyllium and polyethylene glycol, and after a month, still feeling incomplete, he adds senna at night.

6:46His trial has a set length, and failure has a meaning. It runs four to eight weeks, and responders stay on the regimen. Failure of fiber, polyethylene glycol, and stimulants is the strongest clinical clue that the mechanism isn't simple normal-transit constipation. It points to a defecatory disorder, slow transit, or both. That's when to stop escalating laxatives and test with balloon expulsion, anorectal manometry, and a transit study, the subject of episode two. At eight weeks he has a soft bowel movement most days without straining, so he needs no testing.

7:19The second patient shows how alarm features change the order. A fifty-six-year-old woman has four months of new constipation, eight pounds of unintended weight loss, iron deficiency anemia, and no prior colonoscopy. New symptoms after fifty, weight loss, and iron deficiency are each alarm features. She gets a colonoscopy before any empiric trial, because a little improvement on psyllium could delay a cancer diagnosis by months.

7:45The third patient has done everything the first patient did, and it hasn't been enough. A forty-five-year-old woman has chronic idiopathic constipation, chronic constipation without irritable bowel. For three months she's taken psyllium, polyethylene glycol, and senna with only partial relief, and she still has two hard stools a week, with straining. She has no alarm features, a normal colonoscopy this year, and little abdominal pain. Her sphincter relaxes normally when she bears down. She takes no constipating drugs.

8:18Her chronic idiopathic constipation has failed fiber, polyethylene glycol, and stimulants, which is when prescription drugs start. Her normal rectal exam argues against dyssynergia. That makes a trial of prescription drugs reasonable before testing, though it doesn't exclude an outlet problem completely.

8:37Her drug is chosen by what it acts on. The Food and Drug Administration, FDA, approved drugs for chronic idiopathic constipation act at four molecular targets: chloride channel type two, guanylate cyclase-C, the sodium-hydrogen exchanger type three, and the serotonin four receptor. Several are also approved for irritable bowel with constipation, sometimes at different doses. In practice, the choice among them is driven mainly by tolerability, response, and cost, with mechanism deciding what to try after a failure.

9:11The secretagogues are the first group, and they make the gut secrete fluid into the lumen, softening stool and speeding transit. Lubiprostone activates the type two chloride channel, ClC-2, on the surface of intestinal cells. Chloride flows into the lumen, and water follows. The chronic constipation dose is twenty-four micrograms twice daily, three times the irritable bowel dose of eight micrograms twice daily, which is approved only for women. Nausea is the dominant side effect, and taking it with food and water reduces it. Transient chest tightness, described as dyspnea, has been reported. It's contraindicated when mechanical obstruction is suspected.

9:51Linaclotide is the second secretagogue, and it works on a different receptor. It's a guanylate cyclase-C agonist that raises cyclic guanosine monophosphate, GMP, in intestinal cells. That opens the cystic fibrosis transmembrane conductance regulator, CFTR, to secrete chloride and bicarbonate, with water following. Cyclic GMP also reduces pain signaling through submucosal nerves, which is why it eases irritable bowel pain beyond its laxative effect.

10:21Linaclotide's dosing and warnings are specific. The chronic constipation dose is one hundred forty-five micrograms once daily on an empty stomach, at least thirty minutes before the first meal, with a seventy-two microgram dose approved for patients who can't tolerate the higher strength. The irritable bowel dose is two hundred ninety micrograms. Diarrhea is the dominant side effect. It carries a boxed warning for severe dehydration and is contraindicated under age two, and it's approved for pediatric functional constipation from age six.

10:51Plecanatide is the other guanylate cyclase-C agonist, three milligrams once daily for both conditions. It works the same way, with one difference: its activation is pH-dependent, peaking in the slightly acidic small bowel. That may mean marginally less diarrhea in some comparisons, but it hasn't been shown superior to linaclotide head to head. The same pediatric warnings apply.

11:14She starts linaclotide one hundred forty-five micrograms before breakfast. After six weeks she has loose stools on some days but still feels she isn't emptying, and the diarrhea bothers her more than the benefit helps. Timing is checked first, and she's taking it correctly. Loose stools alone would justify stepping down to seventy-two micrograms. But loose stools plus persistent incomplete emptying show that more water in the stool wasn't what she needed.

11:40When a secretagogue fails like this, the move is to switch mechanism, not to try another drug that works the same way. If adding water didn't help, the problem may be weak propulsion. So her next step is prucalopride, a highly selective serotonin four agonist. It increases acetylcholine release from the gut's cholinergic nerves and stimulates high-amplitude propagated colonic contractions. The secretagogues change the stool, and prucalopride changes the colon's pushing.

12:10Prucalopride's dosing is simple. The dose is two milligrams once daily, or one milligram with a creatinine clearance under thirty milliliters a minute, with no adjustment for liver disease. Its common side effects are headache, nausea, abdominal pain, and diarrhea. It's FDA approved for chronic idiopathic constipation but not specifically for irritable bowel with constipation, though it's used in both.

12:32Its class has a history that makes patients and boards wary, and selectivity is the answer. The older serotonin four drugs, cisapride and tegaserod, also acted on the serotonin two-B receptor and on the potassium channel encoded by the human ether-a-go-go-related gene. That caused valvular heart disease, ischemic events, and arrhythmias, and they were withdrawn or restricted. Prucalopride was designed for serotonin four selectivity and has substantially better cardiovascular safety, though baseline cardiovascular risk is still reviewed before starting it. She switches to prucalopride two milligrams, and within three weeks she has a soft stool most days without straining, and the incomplete emptying fades.

13:14The fourth target belongs to a drug that's often offered for the wrong diagnosis. Tenapanor inhibits the sodium-hydrogen exchanger isoform three, NHE3, the main sodium transporter of the small intestine and proximal colon, so sodium and water stay in the lumen and stool softens. It's FDA approved for irritable bowel with constipation, not chronic idiopathic constipation, though it's sometimes used off label. The dose is fifty milligrams twice daily, immediately before the first and last meals. Diarrhea is the dominant side effect. It carries a boxed warning for severe dehydration in children under six, and it's contraindicated with suspected obstruction.

13:56The timing rules differ by drug, and getting them wrong can look like a drug failure. Lubiprostone is taken with food and water. Linaclotide is taken on an empty stomach thirty minutes before the first meal. Tenapanor is taken immediately before the first and last meals. A patient who takes them wrongly may look like a nonresponder when she isn't, which is why timing is checked before any switch.

14:18The last patient shows when switching drugs stops being the answer. A fifty-one-year-old man has failed lubiprostone, then prucalopride alone. Combining a secretagogue with prucalopride is sometimes used in refractory disease, because the mechanisms differ. But after several failures the better question is whether he has a mechanism the drugs can't fix. A defecatory disorder is mechanical, and slow transit may need more than one drug. He needs balloon expulsion and anorectal manometry, and a transit study once an outlet problem is excluded.

14:52Here are the traps the boards set in these patients. Normal frequency doesn't rule out constipation. Constipation driven by dominant abdominal pain is irritable bowel with constipation, not chronic constipation. Not every patient is tested before treatment, but a patient with alarm features isn't treated empirically. Psyllium is preferred over bran. And constipating drugs, such as calcium channel blockers, calcium supplements, iron, and ondansetron, are looked for and stopped.

15:21The laxative traps follow. Stimulants aren't avoided out of fear of colon damage. Magnesium isn't given in kidney disease. And laxatives aren't escalated after a failed four-to-eight-week trial, because failure is the signal to test.

15:35The prescription drug traps close the list. The irritable bowel dose of lubiprostone, eight micrograms, is too low for chronic constipation. Lubiprostone is taken with food, and linaclotide isn't. Linaclotide and plecanatide aren't given under age two, and none of these drugs are given with suspected obstruction. Prucalopride isn't avoided because of cisapride's history, and its dose is halved in severe kidney disease. Tenapanor isn't a chronic idiopathic constipation drug. And after a failure, a second drug with the same mechanism isn't the next step.

16:09So, start to finish. Diagnose chronic constipation from the Rome four symptom cluster, not frequency alone, and separate it from irritable bowel by the absence of dominant pain. Most patients have normal transit, and the rest have slow transit, a defecatory disorder, or both.

16:26Without alarm features, treat empirically: education, psyllium, removing constipating drugs, polyethylene glycol, then stimulants, which are safe long term. With alarm features, investigate first. Failure after four to eight weeks is the signal to test.

16:44When fiber, polyethylene glycol, and stimulants fail, choose a prescription drug by mechanism. Lubiprostone is twenty-four micrograms twice daily with food. Linaclotide is one hundred forty-five or seventy-two micrograms before the first meal, and plecanatide works the same way. Prucalopride, the selective serotonin four prokinetic, is the choice when secretagogues fail or propulsion is weak. Switch mechanism after a failure, and test for an outlet or transit problem when several drugs fail.

17:15Episode two is the mechanisms the drugs can't fix: dyssynergic defecation, slow-transit constipation, and opioid-induced constipation.

17:25For the full chapter, the practice vignettes, and the topic-tagged question bank, head to board pearls dot com. You'll find the rest of the series on Apple Podcasts, Spotify, or wherever you listen to podcasts. That brings us to the end of episode one of three of chapter sixteen, and I'll see you in the next one.