IBS and Functional Bowel: IBS and Functional Bowel: Constipation Subtype

0:00Welcome to Board Pearls. This is episode one of two of the Irritable Bowel Syndrome and Functional Bowel chapter, in the Stomach and Small Bowel Disorders module. This episode is irritable bowel syndrome with constipation. One woman carries it from the first visit. Her case shows how the diagnosis is made from the symptom pattern, how the subtype is assigned, what testing she does and doesn't need, why she hurts and why she's constipated, and how her treatment steps up from there. Episode two does the same for irritable bowel with diarrhea, then covers the patient whose main problem is pain or bloating, whatever the stool pattern.

0:37Here's the patient. A thirty-four-year-old woman has had crampy lower abdominal pain for about a year. It comes on most weeks, it's tied to her bowel movements, and when it flares her stools are hard and lumpy and come every three or four days. She's bloated by evening. She hasn't lost weight, she sleeps through the night, there's no blood, and nobody in her family has had colon cancer, inflammatory bowel disease, or celiac disease. Her exam is normal.

1:05Her story suggests irritable bowel syndrome, and whether it is comes from the history. Irritable bowel is a positive diagnosis. It's made from the symptom pattern, not by excluding every other disease first, because there's no blood test or scope finding that proves it. It's a disorder of brain-gut interaction, in which disturbed motility, visceral hypersensitivity, altered permeability, microbiome shifts, and central pain processing combine in different proportions to produce pain plus disordered defecation.

1:35The pattern is defined by the Rome four criteria. She needs recurrent abdominal pain, on average at least one day a week over the last three months, with symptoms that started at least six months ago. The pain has to connect to her bowels in at least two of three ways: it's related to defecation, it comes with a change in how often she goes, or it comes with a change in what the stool looks like.

1:57Two details of the wording catch people out. The criteria require pain, not the older "pain or discomfort," and at least one day a week, stricter than the older three days a month. And the wording is related to defecation, not relieved by it, because some patients hurt more when they go, and they still have irritable bowel.

2:19Pain is the requirement that separates her from the patient with chronic constipation. A patient with hard, infrequent stools and bloating but little or no pain has chronic idiopathic constipation, not irritable bowel. The distinction matters at the pharmacy, because some of the same drugs are dosed differently or approved for only one of the two. She has pain most weeks, tied to defecation and to stool form, so she meets the criteria.

2:45With the diagnosis made, her subtype has to be assigned, because the drugs for constipation and the drugs for diarrhea push the bowel in opposite directions, and most prescription drugs are approved for only one subtype. She's classified by the Bristol stool form on the days her bowel movements are abnormal, not on all days. Bristol one and two are the hard pellets and lumpy logs. Bristol six and seven are mushy and watery.

3:13The thresholds are each a quarter of abnormal movements. She has constipation-predominant disease if at least a quarter of her abnormal movements are Bristol one or two and fewer than a quarter are six or seven. Diarrhea-predominant disease is the reverse. Mixed disease has at least a quarter at each end. Unclassified disease meets the pain criteria but can't be subtyped by stool pattern. Hers are hard and lumpy on the bad days and never loose, so she has irritable bowel with constipation.

3:44Before the label is applied, alarm features are checked, because they call for testing first. They're new bowel symptoms after age fifty; unintentional weight loss, typically more than ten percent of body weight over three months; symptoms that wake her at night; blood in the stool or iron deficiency; fever; a family history of colorectal cancer, inflammatory bowel disease, or celiac disease; an abnormal exam, such as a mass, an abnormal rectal exam, or enlarged lymph nodes; and travel to a region where parasites are common. Older lists also include progressive dysphagia and severe chronic constipation.

4:19Any one of those means directed testing first. It doesn't rule out irritable bowel, but it changes how much testing comes before the label. She has none.

4:29Without alarm features, her subtype means there's nothing to send. Unlike the diarrhea subtype, constipation-predominant disease has no recommended screening labs: no blood count, no thyroid panel, no imaging, no stool studies. The only test she needs is whatever colon cancer screening her age calls for, which starts at forty-five in average-risk adults, so at thirty-four she needs nothing. A colonoscopy is for alarm features or age-based screening, never a routine part of the irritable bowel workup.

4:59One more question comes before treatment, and it's about how she empties, because the answer can change the whole plan. She's asked whether she strains hard, feels she hasn't finished, spends a long time on the toilet, or has to press on the perineum or use a finger to get stool out. Those point to pelvic floor dyssynergia, in which the abdominal push and the anal relaxation don't happen together. That's a mechanical problem at the outlet. It doesn't respond well to laxatives, and it needs anorectal manometry with a balloon expulsion test and then biofeedback. If she says yes to those questions early, she's tested before drugs are escalated. She says no, so treatment goes ahead.

5:37Why she has symptoms decides her treatment, because each mechanism is a treatment target. Her two problems, the pain and the bowel habit, come from different places.

5:47Her pain comes mainly from visceral hypersensitivity, a gut that registers ordinary stretching as painful. When a balloon is inflated in the rectum, about two-thirds of patients with irritable bowel feel pain at smaller volumes than healthy people do. The sensitivity is raised in two places. In the gut wall, mast cells, enterochromaffin cells, and sensory nerve endings are primed by inflammation, bile acids, bacterial products, and food, so the nerves and the spinal cord neurons they feed fire at lower inputs.

6:20The second place is the brain. On functional imaging, the same gut signal activates pain-processing regions, the insula, anterior cingulate, and prefrontal cortex, more strongly than it does in controls. So there are two ways to treat her pain: calm the gut nerves, or turn down the central amplification.

6:38Her constipation comes from the colon itself. In constipation-predominant disease, transit is slow, and there are fewer of the high-amplitude contractions that sweep stool down the colon. Those contractions depend on acetylcholine released by the enteric nerves, and a serotonin-four receptor on those nerves increases that release. That receptor is the target when the colon won't move. The other way to fix hard stool is to get more water into it, either by making the intestine secrete water or by stopping it from absorbing sodium.

7:10So her treatment has three targets: water in the lumen, a colon that moves, and nerves that are less sensitive. She starts with the simplest steps, and more is added only when they fail.

7:21The first step costs nothing. She's told what she has, in plain words, and that it's real and common and not dangerous. A clear diagnosis and a good relationship with her doctor improve symptoms on their own and reduce visits. Then her medication list is checked, and anything that constipates is stopped or reduced: opioids, anticholinergics, calcium channel blockers, iron, and calcium supplements.

7:47Then comes fiber, and the type matters. Soluble fiber, psyllium, helps irritable bowel. It's started low and increased slowly toward about twenty-five grams a day, because a fast increase makes bloating worse. Insoluble fiber like wheat bran usually makes bloating and pain worse in these patients without helping much. So if she's already eating bran cereal every morning and feels worse, she's switched to psyllium. Fluids, regular exercise, and scheduled toileting round it out.

8:18If she's still constipated, polyethylene glycol is added, over the counter. It holds water in the stool by osmosis and makes her go more often, but it does little for pain. That gap is why the prescription drugs exist. When pain and constipation come together, the right drug adds water to the lumen and also quiets the gut's sensory nerves.

8:40The prescription drugs that add water are called secretagogues. They're chosen among by tolerability, response, and cost, because they all work, and the mechanism matters mostly when one fails.

8:53Linaclotide and plecanatide are the first pair, and they treat both of her problems. They stimulate guanylate cyclase C on the lining cells. That raises cyclic guanosine monophosphate, GMP, which opens the cystic fibrosis transmembrane conductance regulator, CFTR, a chloride channel, and drives chloride and bicarbonate into the lumen, and water follows. The same signal quiets the sensory nerves under the lining, which is why these two drugs improve pain as well as constipation.

9:22Their dosing and warnings differ slightly. Linaclotide is two hundred ninety micrograms once a day, on an empty stomach at least thirty minutes before the first meal. Plecanatide is three milligrams once a day, with or without food. Diarrhea is the main side effect of both. Both carry a boxed warning for dehydration in young children, and linaclotide is contraindicated under age two and plecanatide under age six. Plecanatide's activation depends on pH, which may give it a slightly lower diarrhea rate in some comparisons, though neither drug has proved superior head to head.

9:57Lubiprostone activates a different chloride channel, the type two chloride channel, with the same result. For irritable bowel with constipation the dose is eight micrograms twice a day, and it's approved only in women, because the trials enrolled mostly women. For chronic idiopathic constipation the dose is twenty-four micrograms twice a day, three times higher, which is the classic dosing trap.

10:20Lubiprostone's main side effect is nausea, and taking it with food reduces that. So if she's nauseated on lubiprostone and has been taking it on an empty stomach, it's moved to mealtimes before it's called a failure. It's contraindicated when mechanical obstruction is suspected.

10:38Tenapanor adds water the other way around. Instead of driving secretion, it blocks the sodium-hydrogen exchanger isoform three, NHE3, which absorbs sodium in the small intestine and proximal colon, so sodium stays in the lumen and holds water with it. It also seems to lower visceral sensitivity. The dose is fifty milligrams twice a day, before breakfast and before dinner. Diarrhea is the main side effect. It carries a boxed warning and is contraindicated under age six, and like lubiprostone, it's contraindicated when mechanical obstruction is suspected.

11:12If the secretagogues fail, or if the history and testing say the colon itself is slow, the next step is a prokinetic. Prucalopride is a selective serotonin-four agonist. It increases acetylcholine release from the enteric nerves and restores the high-amplitude contractions a slow colon lacks. The dose is two milligrams once a day, or one milligram in renal impairment. It's approved for chronic idiopathic constipation rather than irritable bowel, so for her it's off label, but it's a reasonable choice when slow transit dominates. Headache, nausea, abdominal pain, and diarrhea are the common side effects.

11:50Its safety comes from its selectivity. Older drugs aimed at the same receptor, cisapride and tegaserod, also hit the serotonin two-B receptor and a cardiac potassium channel, which caused arrhythmias and ischemic events, and they were withdrawn or restricted. Prucalopride was built to avoid those targets and has a better cardiovascular record, though her cardiac risk is still reviewed before starting it.

12:13If pain is still the main problem after her bowels are moving, treatments aimed at pain itself are added, and her subtype shapes the choice. If an antidepressant is chosen as a pain modulator, a selective serotonin reuptake inhibitor, SSRI, fits better than a tricyclic. SSRIs tend to speed transit, while tricyclics slow it and would make her constipation worse. The evidence for SSRIs here is weaker than for tricyclics in diarrhea, and they're often chosen when a mood disorder is also present. Enteric-coated peppermint oil and behavioral therapy work on pain in every subtype.

12:50Here are the traps the boards set in this patient. Irritable bowel requires pain, so hard stools and bloating without pain are chronic constipation. Pain that worsens with defecation still counts. The subtype is set by stool form on abnormal days, not all days. And alarm features don't rule out irritable bowel, but they do mean testing first.

13:11The workup traps follow. A young patient with constipation and no alarm features needs no labs, no imaging, and no colonoscopy. And a patient who strains, feels incomplete, and splints needs manometry and biofeedback, not more laxatives.

13:27The treatment traps close the list. Bran isn't the fiber to add, because psyllium is. Lubiprostone for irritable bowel is eight micrograms, not the chronic constipation dose of twenty-four, and it isn't abandoned before it's tried with food. Linaclotide is taken on an empty stomach. Prucalopride is for a slow colon or failed secretagogues, and it's off label here. And a tricyclic isn't added for pain in a patient who's already constipated.

13:54So, start to finish. Make the diagnosis from the pattern: pain at least weekly, tied to defecation or to a change in stool frequency or form, for six months. Call it constipation-predominant from the Bristol form on the bad days.

14:07Check alarm features, and with none, test nothing beyond age-based cancer screening, but ask about straining and incomplete evacuation.

14:16Then treat in order: explanation, stopping constipating drugs, psyllium, and polyethylene glycol. Add a secretagogue when pain and constipation travel together, and prucalopride when those fail or the colon is slow. If pain persists, an SSRI fits her subtype better than a tricyclic.

14:35Episode two follows a patient with the opposite problem, irritable bowel with diarrhea, and then the treatments for pain and bloating in every subtype. That's where the testing matters, because several treatable diseases imitate it, and the treatment depends on what's driving the diarrhea.

14:51For 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 two of chapter thirteen, and I'll see you in the next one.