IBS and Functional Bowel: IBS and Functional Bowel: Diarrhea and Bloating

0:00Welcome to Board Pearls. This is episode two of two of the Irritable Bowel Syndrome and Functional Bowel chapter, in the Stomach and Small Bowel Disorders module. This episode covers irritable bowel syndrome with diarrhea, then the patient whose main problem is pain and bloating, in any subtype. A young man with loose stools and cramps has irritable bowel with diarrhea, and his case shows how the diagnosis is made, which tests he needs, which treatable diseases could be imitating it, why he has diarrhea, and how his treatment is chosen from what's driving it. A man with the mixed subtype, fibromyalgia, and migraines shows why the subtype drugs don't fit him, how pain is treated through the gut and the brain, and how bloating is worked up from the lumen outward.

0:40Here's the first patient. A twenty-nine-year-old man has had crampy lower abdominal pain and loose stools for about a year. On bad days he goes four or five times, the stool is mushy or watery, and he often has to run to the bathroom within minutes of eating. The pain eases somewhat after he goes. He has no blood in the stool, he hasn't lost weight, and he never wakes at night to go. His exam is normal.

1:04His story suggests irritable bowel syndrome with diarrhea, and it's a positive diagnosis made from the symptom pattern, not a diagnosis of exclusion. By the Rome four criteria he needs recurrent abdominal pain 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 his bowels in at least two of three ways: related to defecation, with a change in stool frequency, or with a change in stool form. He meets all three.

1:32His subtype is set by his stool form on bad days, because the drugs split by subtype. Diarrhea-predominant means at least a quarter of his abnormal movements are Bristol six or seven, mushy or watery, and fewer than a quarter are Bristol one or two. His are loose on bad days and never hard.

1:49Before the label is applied, alarm features are checked, because they change the testing. They're new symptoms after fifty; unintentional weight loss, typically more than ten percent of body weight over three months; nocturnal symptoms that wake the patient; blood or iron deficiency anemia; fever; a family history of colorectal cancer, inflammatory bowel disease, or celiac disease; an abnormal exam, such as a mass or lymph nodes; and travel to a region where parasites are common. Nocturnal diarrhea and weight loss deserve special attention, because functional bowel disease follows the day-night cycle and rarely causes weight loss. An alarm feature doesn't rule out irritable bowel, but it means directed testing first. He has none.

2:33Even with no alarm features, a patient with diarrhea gets a short screen, because a few common diseases cause exactly this picture. A tissue transglutaminase immunoglobulin A, IgA, is sent with a total IgA level for celiac disease. Celiac disease is several times more common in irritable bowel populations, and IgA deficiency is more common in celiac disease and makes the antibody falsely negative. A C-reactive protein, CRP, and a fecal calprotectin screen for inflammatory bowel disease. A Giardia stool antigen or polymerase chain reaction, PCR, is sent with an exposure, such as travel or daycare.

3:14The rest of the old workup adds little. Some guidelines add fecal lactoferrin, and a lactose breath test is an option if lactose remains a concern after a diet trial. A blood count, chemistries, thyroid tests, imaging, and broad ova and parasite panels don't help without a specific reason.

3:33An abnormal screen sends the workup to that disease instead. A positive celiac antibody goes to duodenal biopsy, and a high calprotectin goes to colonoscopy. Colonoscopy is otherwise for alarm features and age-based screening from forty-five, not part of a routine irritable bowel workup. His screen is normal.

3:53A normal screen doesn't end it, because several treatable diseases slip past it, each with a clue in the history. An older patient on a proton pump inhibitor, PPI, a selective serotonin reuptake inhibitor, SSRI, or a nonsteroidal anti-inflammatory drug, NSAID, with watery, nonbloody diarrhea and a normal-looking colon, has microscopic colitis until random colon biopsies say otherwise.

4:20Bile acids are the mimic most often mistaken for irritable bowel itself. Watery diarrhea after a cholecystectomy, after an ileal resection, or with ileal Crohn disease points to bile acid diarrhea. It hides inside up to thirty percent of patients labeled diarrhea-predominant irritable bowel, because excess bile acids reaching the colon drive secretion and motility. A quick response to a bile acid sequestrant both makes and treats the diagnosis.

4:47What he eats can point to other mimics. Symptoms after milk products point to lactose maldigestion, and after fruit, honey, or sweetened drinks to fructose, both confirmed with a breath test or a dietary trial. Sucrose maldigestion from sucrase-isomaltase deficiency is found in about seven percent of unexplained diarrhea-predominant cases in American series. It's diagnosed by enzyme activity on a duodenal biopsy and treated with sucrose restriction and enzyme replacement with sacrosidase.

5:18Two more mimics have distinctive clues. Symptoms starting hours after mammalian meat or dairy, in someone bitten by lone star ticks in the southeastern or midwestern United States, point to alpha-gal syndrome. That's an immunoglobulin E, IgE, mediated reaction to a sugar in mammalian meat, diagnosed with a serum alpha-gal IgE. Bloating and diarrhea with a low B12 and a high folate point to small intestinal bacterial overgrowth.

5:47The timing of onset can reveal one more cause. Symptoms that began after gastroenteritis suggest post-infectious irritable bowel. About ten percent of patients develop it in the year after a bacterial enteritis, and it's even more common after C. difficile infection. It comes from low-grade mucosal inflammation, altered enteroendocrine cells, and a microbiome that doesn't reset. A more severe or longer infection, female sex, younger age, anxiety or depression at the time, and antibiotics during the illness raise the risk.

6:20Post-infectious symptoms set a testing trap. Retesting for C. difficile in a patient with typical post-infectious irritable bowel symptoms, but no features of active C. difficile infection, misleads, because thirty to fifty percent of positive results in that setting are false positives. A careful history is the right move. He has none of these clues, so he has irritable bowel with diarrhea.

6:43His treatment depends on why he has diarrhea, because the drugs target specific mechanisms. In diarrhea-predominant disease, colonic transit is fast and the colon overreacts to eating, which is why he has urgency within minutes of a meal. His gut microbiome is altered, with less diversity, and bacterial fermentation adds gas and loose stool. His pain comes from visceral hypersensitivity, a gut that registers normal stretching as pain, amplified by the brain.

7:10So treatment has four possible targets, transit, the microbiome, bile acids, and pain, and the drug is chosen by which symptom bothers him most. Before any drug, the diagnosis is explained, and a trial of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, a low-FODMAP diet, is considered.

7:32His frequency and urgency are treated first, with loperamide. It's a mu-opioid agonist that acts on the gut without crossing into the brain, two to four milligrams as needed, up to sixteen milligrams a day, and it's well tolerated long term. It controls frequency and urgency, not pain, which is why later drugs target other mechanisms.

7:53If bloating and overall symptoms persist, rifaximin acts on the microbiome. It's five hundred fifty milligrams three times a day for fourteen days, and it improves overall symptoms and bloating by about ten percentage points over placebo. It reduces bacterial fermentation in the small bowel and colon. Less than zero point four percent is absorbed, so its safety is benign and resistance hasn't become a clinical problem.

8:19Rifaximin's benefit can be renewed. If he responds and relapses months later, the same course is repeated, and the label allows up to two retreatments, three courses in all. Rifaximin is for the diarrhea subtype, not constipation.

8:33When the history points to bile acids, a sequestrant comes first. Cholestyramine is four grams once to four times a day. Colesevelam, as tablets or a powder, is better tolerated, and colestipol is a third option. A response within days to a couple of weeks means bile acid diarrhea was probably the real driver, and the label should be revisited. Sequestrants bind other drugs, so doses are separated by several hours, and long-term high doses can cause fat-soluble vitamin malabsorption.

9:04If those fail, eluxadoline is the next option, but only for the right patient. It's a mu and kappa opioid agonist and delta antagonist that slows transit and lowers visceral sensitivity without the constipation of a pure opioid. It's one hundred milligrams twice a day, or seventy-five milligrams for patients who can't tolerate the higher dose, in mild to moderate liver impairment, or with drugs that block the liver transporter OATP1B1.

9:32Its contraindications come from the sphincter of Oddi. Eluxadoline can cause spasm of the sphincter of Oddi. With a gallbladder, the gallbladder absorbs the pressure, but without one, the spasm causes pancreatitis and severe biliary pain. So it's contraindicated after cholecystectomy. It's also contraindicated with biliary obstruction or sphincter of Oddi disease, more than three drinks a day or binge drinking, prior pancreatitis or structural pancreatic disease, severe liver impairment, and a history of severe constipation.

10:03The board patient is the one without a gallbladder, or with heavy drinking, who starts eluxadoline and returns with epigastric pain and a high lipase. After a cholecystectomy, a bile acid sequestrant trial was the better step anyway.

10:18Alosetron is the last step in this subtype, but not for him. It's a serotonin-three antagonist that slows colonic transit and lowers visceral sensitivity. It's approved only for women with severe diarrhea-predominant disease refractory to other treatment, started at half a milligram twice a day and increased to one milligram twice a day. It was withdrawn in two thousand for severe constipation and ischemic colitis, then brought back under a Risk Evaluation and Mitigation Strategy program with restricted prescribing.

10:49Alosetron's limits rule him out. It isn't used in the mixed subtype, because of the constipation risk, or in men, because the trials in men didn't show benefit. Ondansetron, another serotonin-three antagonist, has some off-label benefit and is sometimes used when alosetron isn't available, but it isn't approved for this.

11:09If pain dominates, a low-dose tricyclic is added, and it fits his subtype especially well. Amitriptyline ten to thirty milligrams at bedtime works on pain processing, not mood, at doses below those for depression. A large primary care trial confirmed that amitriptyline at that dose relieves irritable bowel without depending on any change in mood. Its anticholinergic effect slows transit, which helps diarrhea and would hurt a constipated patient.

11:37The second patient has the mixed subtype, and his main problems are pain and bloating. A forty-seven-year-old man has had irritable bowel for years. His stools alternate, some weeks hard and some weeks loose, at least a quarter at each end of the Bristol scale, so he has the mixed subtype. His alarm features have always been negative, his celiac antibody and calprotectin were normal, and his screening colonoscopy at forty-five was clean. He's tried fiber, loperamide on loose days, and polyethylene glycol on hard days.

12:11What bothers him now is crampy pain most days, and a belly that swells by evening until he has to loosen his belt. He also has fibromyalgia and migraines.

12:21His mixed subtype changes the approach. Most prescription drugs are approved for only one subtype, and a drug for one end of his stool pattern risks pushing him to the other. So his care leans on treatments that target shared mechanisms in every subtype, aimed at the symptom that bothers him most, which is pain.

12:38His pain comes from visceral hypersensitivity. In rectal balloon studies, about two-thirds of patients with irritable bowel feel pain at smaller volumes than controls, from sensitization in the gut wall and in the brain. On functional imaging, the same gut input activates pain-processing regions more strongly in irritable bowel than in healthy people.

12:59That central amplification is why his fibromyalgia and migraines matter. Irritable bowel often comes with fibromyalgia, interstitial cystitis, migraine, and chronic pelvic pain, which share heightened central pain processing. So a treatment aimed at the central pathway can help all of them.

13:17Psychological distress shapes his experience but doesn't explain it. Anxiety, depression, and past trauma are more common in referral clinic patients, but people with irritable bowel in the community who never see a doctor are psychologically like everyone else. Distress doesn't cause irritable bowel. It shapes the experience of it and drives care-seeking.

13:37His pain can be treated three ways: drugs that relax gut smooth muscle, drugs that turn down pain processing, and behavioral therapy. Each acts on a different part of the mechanism.

13:48The antispasmodics are the most prescribed and the least supported. Dicyclomine and hyoscyamine are anticholinergics used in short bursts during cramping. Their benefit over placebo is small, and their side effects are real: dry mouth, blurred vision, trouble urinating, and confusion in older adults. Hyoscine butylbromide is used more in Europe, and mebeverine, which isn't anticholinergic, is used outside the United States.

14:15One antispasmodic has strong evidence. Enteric-coated peppermint oil, containing L-menthol, relaxes intestinal smooth muscle by blocking calcium channels, and it reduces pain and bloating in several randomized trials. The coating matters, because uncoated oil dissolves in the stomach and causes reflux. The dose is one hundred eighty to two hundred twenty-five milligrams three times a day, and heartburn remains the main side effect in some patients even with the coating.

14:43A neuromodulator works by lowering visceral sensitivity and central pain amplification, not by treating depression. So the dose is lower than an antidepressant dose, the response takes weeks, and the drug is chosen by matching its side effects to the stool pattern.

14:59Each class fits a different patient. A low-dose tricyclic suits diarrhea-predominant disease: amitriptyline ten to thirty milligrams, nortriptyline ten to fifty, or desipramine twenty-five to one hundred, at bedtime. An SSRI suits constipation-predominant disease because it tends to speed transit, though the evidence is weaker, and it fits when depression or anxiety coexists. Mirtazapine fits a diarrhea-predominant patient with nausea or insomnia.

15:27His neuromodulator is chosen for his whole picture. A serotonin-norepinephrine reuptake inhibitor, duloxetine in particular, works in any subtype and fits best when fibromyalgia, chronic pelvic pain, or migraine accompanies irritable bowel. With alternating stools, fibromyalgia, and migraine, duloxetine is the best fit for him, because it works across subtypes and acts on the central pain pathway shared by all three conditions. He's told to expect weeks, not days, before judging it.

15:57Behavioral therapy has stronger evidence than most people expect. Cognitive behavioral therapy, CBT, targets catastrophizing, hypervigilance to gut sensations, and avoidance of food and activities. It brings global improvement in fifty to seventy percent, with benefit lasting six to twelve months after treatment ends.

16:19Gut-directed hypnotherapy has the most consistent trial data. It's usually seven to twelve sessions, with response in fifty to seventy percent and benefit lasting one to five years. It appears to work by reducing central pain amplification and autonomic reactivity, and imaging afterward shows changes in the insula and anterior cingulate, regions that process gut signals.

16:42Behavioral therapy belongs early for refractory disease, not as a last resort. Mindfulness-based stress reduction, dynamic psychotherapy, relaxation training, and biofeedback are other options, and structured psychological therapy works about as often as an antidepressant. After failed subtype drugs and a neuromodulator, hypnotherapy or CBT is a first-line option for refractory disease, not a fifth drug. Refractory patients do best with integrated care: a gastroenterologist, a dietitian, a behavioral health clinician, and a pelvic floor physical therapist when needed.

17:18Two microbiome treatments don't earn a place. Probiotics have modest, inconsistent benefit, with no strain that reliably helps. Fecal microbiota transplant shouldn't be offered, because randomized trials show it doesn't work for irritable bowel.

17:34His bloating is worked up separately, starting with what he means. Bloating is the sensation of fullness and pressure. Distension is a visible, measurable increase in girth, by tape measure or by inductance plethysmography. About half of patients who feel bloated have measurable distension. He has both. The causes are either too much in the lumen, gas, fluid, or stool, or an abdominal wall and diaphragm that behave abnormally, and the lumen is checked first.

18:01Constipation is checked first, even in a mixed-subtype patient, because retained stool is the most common reversible cause of bloating and distension, and treating it often resolves the bloating.

18:12How he empties is checked next, because incomplete evacuation keeps the colon loaded. Straining, a sense of incomplete evacuation, long toilet sessions, and needing to press or use a finger to pass stool point to pelvic floor dyssynergia, an inability to coordinate the abdominal push with anal relaxation. Anorectal manometry with a balloon expulsion test makes the diagnosis, and biofeedback treats it.

18:37Bacterial overgrowth is the next luminal cause. A glucose or lactulose breath test looks for it, and it contributes to bloating in some patients, which is the rationale for rifaximin's benefit. Methane-predominant overgrowth goes with constipation, and rifaximin plus neomycin is sometimes used when methane dominates, though the evidence is limited.

18:57Food is where most bloating treatment happens. The low-FODMAP diet removes short-chain carbohydrates the small bowel absorbs poorly. They draw water into the lumen and are fermented into gas in the colon. They're fructans, in wheat, onions, garlic, and artichokes; galacto-oligosaccharides, in beans and lentils; lactose, in milk products; excess fructose, in apples, pears, honey, and high-fructose corn syrup; and polyols, such as sorbitol, mannitol, sugar-free gum, and stone fruits. Fifty to seventy percent improve, in every subtype.

19:35The diet has three phases, and the phases are what make it safe. First, all the groups are eliminated for four to six weeks. Then each group is reintroduced separately over the next four to eight weeks. Then only the triggers are restricted. A dietitian should guide it, because blanket restriction indefinitely is nutritionally harmful, changes the microbiome, and is more restrictive than needed. Soluble psyllium helps, and insoluble wheat bran often makes bloating worse. An over-the-counter enzyme product that breaks down FODMAPs exists, but randomized human data are limited.

20:10When the lumen is clear and the belly still protrudes, the problem is the abdominal wall. He isn't constipated, empties normally, has a negative breath test, and the diet helped only a little. Yet his belly visibly protrudes by evening, and he can pull it back in when examined during an episode. That's abdomino-phrenic dyssynergia. When he feels bloated, his diaphragm descends paradoxically while his abdominal wall relaxes, so the belly pushes out without any increase in volume.

20:41His treatment is physical, not dietary. It's physical therapy with diaphragmatic breathing retraining and abdominal wall exercises, with several small randomized trials showing benefit. The twenty twenty-three American Gastroenterological Association update on bloating recommends looking for it and treating it.

21:01Here are the traps the boards set in these patients. The celiac antibody isn't skipped, and it isn't sent without a total IgA. Irritable bowel isn't diagnosed with an elevated calprotectin. Microscopic colitis is missed when nobody biopsies a normal-looking colon in an older patient on a PPI or SSRI. Bile acid diarrhea is missed after a cholecystectomy. And C. difficile isn't retested in post-infectious symptoms.

21:29The diarrhea drug traps follow. Loperamide doesn't treat pain. Rifaximin can be repeated twice. Eluxadoline isn't given without a gallbladder or with heavy drinking. And alosetron isn't prescribed to a man or in the mixed subtype.

21:44The pain and bloating traps close the list. The mixed subtype isn't treated with a subtype drug instead of the active symptom. Peppermint oil has to be enteric-coated. A neuromodulator isn't judged after a week, and a tricyclic isn't chosen for a constipated patient. Behavioral therapy isn't overlooked for refractory pain. Fecal transplant isn't offered. Low-FODMAP restriction isn't left in place forever. And bloating isn't worked up without first checking for constipation and incomplete evacuation.

22:12So, start to finish. Make the diagnosis from the pattern, and call it diarrhea-predominant from the Bristol form on bad days. With no alarm features, send a narrow screen: transglutaminase IgA with total IgA, CRP and calprotectin, and Giardia testing with exposure. Ask the history questions for microscopic colitis, bile acid diarrhea, sugar maldigestion, alpha-gal, bacterial overgrowth, and post-infectious disease.

22:39Then treat by the dominant symptom. Loperamide treats frequency and urgency, rifaximin treats bloating and overall symptoms, and a sequestrant treats likely bile acid diarrhea. Eluxadoline is only for patients with a gallbladder and without heavy drinking. Alosetron is only for women with severe refractory disease. And a low-dose tricyclic treats pain.

23:01Pain in irritable bowel comes from a sensitive gut and an amplifying brain and is treated the same way in every subtype. Use enteric-coated peppermint oil over anticholinergic antispasmodics, a neuromodulator matched to the stool pattern and given weeks to work, and CBT or gut-directed hypnotherapy for refractory pain.

23:22For bloating, separate the feeling from visible distension, then work from the lumen outward: constipation, pelvic floor dyssynergia, bacterial overgrowth, and a three-phase low-FODMAP diet. When the lumen is clear and the belly still protrudes, think of abdomino-phrenic dyssynergia and send the patient to physical therapy.

23:41The next chapter turns to inflammatory bowel disease, where the problem is structural rather than functional. It covers ulcerative colitis severity and acute severe colitis, Crohn disease phenotypes, where the biologics fit, and dysplasia surveillance in long-standing colitis.

23:57For 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 two of two of chapter thirteen, and I'll see you in the next one.