Gastrointestinal

Irritable bowel syndrome: Rome IV diagnosis and management

Clinical Overview and When to Suspect IBS

— Prevalence ~10–12% in US adults; 2:1 female predominance

— Onset typically <50 years; new IBS-type symptoms after 50 require workup for organic disease

— Major driver of outpatient GI visits and a top reason for primary care referral to gastroenterology

— Visceral hypersensitivity, altered motility, intestinal permeability ("leaky gut")

— Microbiome alterations; post-infectious IBS after bacterial gastroenteritis (Campylobacter, Salmonella, Shigella)

— Brain–gut axis dysregulation amplified by anxiety, depression, somatization, prior trauma

— Chronic (≥6 months) abdominal pain that improves or worsens with defecation

— Stool form or frequency changes paralleling pain

— Bloating, mucus in stool, sensation of incomplete evacuation

— No nocturnal symptoms, no weight loss, no GI bleeding, no anemia

— IBS-C: ≥25% hard/lumpy, <25% loose

— IBS-D: ≥25% loose, <25% hard

— IBS-M: ≥25% both

— IBS-U: unclassified

Board pearl: IBS is a positive clinical diagnosis using Rome IV criteria — not a diagnosis of exclusion. Resist ordering broad imaging or endoscopy in a classic young patient without alarm features; over-testing reinforces illness behavior and drives cost without improving outcomes.

Definition: Irritable bowel syndrome (IBS) is a disorder of gut–brain interaction characterized by recurrent abdominal pain associated with defecation and/or altered bowel habits, without structural or biochemical abnormality on routine evaluation.

Epidemiology:

Pathophysiology (mixed mechanisms):

When to suspect IBS in primary care:

Subtypes (by predominant stool form on symptom days, Bristol scale):

Comorbid clustering: fibromyalgia, chronic fatigue, migraine, interstitial cystitis, GERD, anxiety/depression, dyspareunia

Cost & quality of life: comparable disability to diabetes or CHF; high absenteeism

Presentation Patterns and Key History

— Recurrent abdominal pain ≥1 day/week on average in the last 3 months

— Symptom onset ≥6 months before diagnosis

— Associated with ≥2 of 3: (1) related to defecation, (2) change in stool frequency, (3) change in stool form/appearance

— Note: Rome IV replaced "discomfort" with pain and dropped the "improves with defecation" wording (can improve OR worsen)

— Pain: crampy, lower abdomen/LLQ, often postprandial; rarely awakens patient from sleep

— Bowel habits: alternating, urgency, straining, mucus, incomplete evacuation

— Triggers: stress, meals (FODMAPs, fatty foods, caffeine, alcohol), menses

— Relief with flatus or bowel movement

— Age ≥50 at symptom onset

— Unintentional weight loss (>10% body weight)

— Hematochezia, melena, or iron-deficiency anemia

— Nocturnal diarrhea or pain

— Fever, progressive symptoms

— Family history of CRC, IBD, or celiac disease

— Palpable mass, lymphadenopathy

— Screen for anxiety/depression (PHQ-9, GAD-7) — present in 40–60%

— History of physical/sexual abuse correlates strongly

— Sleep quality, work/school impact, prior healthcare utilization

Key distinction: Functional pain in IBS is reproducibly linked to defecation or stool changes. Pain that is constant, progressive, nocturnal, or unrelated to bowel habits should redirect you toward organic disease (IBD, malignancy, chronic pancreatitis, endometriosis).

Rome IV criteria (must memorize for Step 3):

Symptom characterization to elicit:

Alarm ("red flag") features — mandate workup beyond IBS:

Psychosocial history:

Dietary diary: 1–2 week food/symptom log identifies trigger patterns and lays groundwork for low-FODMAP trial

Medication review: opioids → constipation; metformin, SSRIs, magnesium → diarrhea; NSAIDs → mimics

Physical Exam Findings (and Severity Assessment)

— Should be normal; fever, tachycardia, orthostasis point away from IBS

— Weight trend on chart review — stable weight supports functional etiology

— Soft, possibly mildly tender along colonic distribution (LLQ most common)

— Palpable, tender sigmoid cord is classic but nonspecific

— Mild distention/bloating; bowel sounds normal

— Should NOT have: rigidity, guarding, rebound, palpable masses, hepatosplenomegaly, ascites, visible peristalsis

— Inspect for fissures, hemorrhoids, fistulae (suggest IBD)

— DRE: assess resting and squeeze tone, paradoxical puborectalis contraction (dyssynergic defecation mimics IBS-C)

— Stool for occult blood — positive FOBT is a red flag

— Oral aphthous ulcers, episcleritis, erythema nodosum, pyoderma gangrenosum → IBD

— Dermatitis herpetiformis → celiac disease

— Skin hyperpigmentation, postural hypotension → adrenal insufficiency mimicker

— Lymphadenopathy, thyromegaly

— Mild: intermittent symptoms, no daily impact — diet/lifestyle alone

— Moderate: regular symptoms, some QOL impact — add pharmacotherapy

— Severe: refractory, frequent healthcare use, psychiatric comorbidity — multidisciplinary care including behavioral health and GI

Board pearl: A completely benign exam plus Rome IV criteria plus absence of alarm features in a patient <50 is sufficient to make the IBS diagnosis and begin therapy — additional testing beyond a minimal panel does not improve diagnostic yield (<2% organic disease found).

General principle: Exam in IBS is typically normal or near-normal. Its purpose is to exclude organic disease and to build therapeutic alliance through a careful, hands-on encounter.

Vital signs:

Abdominal exam:

Anorectal exam (often skipped, but high-yield):

Extraintestinal clues that argue AGAINST IBS:

Severity stratification (informs management intensity):

Diagnostic Workup — Initial Labs and Limited Testing

— CBC — rule out anemia (would suggest blood loss, IBD, malignancy)

— CRP or fecal calprotectin — distinguishes IBS from IBD; calprotectin <50 µg/g essentially excludes IBD

— Celiac serology (tTG-IgA + total IgA) — particularly in IBS-D and IBS-M; celiac is 4× more common in IBS-D presentations

— TSH — only if clinical suspicion (not routine per ACG)

— Fecal calprotectin or lactoferrin

— Giardia antigen if exposure risk (camping, daycare, travel, immigrants)

— Consider bile acid diarrhea workup (serum 7α-hydroxy-4-cholesten-3-one or therapeutic trial of bile acid sequestrant) in chronic watery diarrhea

— Stool ova & parasites in low-risk patients

— Food allergy/IgG sensitivity panels — no evidence base; do not order

— Routine abdominal CT, ultrasound, or MRI

— Hydrogen breath testing for SIBO — controversial; not routine

— Lactose breath test — empirical lactose-free trial is more practical

— Age ≥45 (CRC screening — kill two birds)

— Any alarm feature

— IBS-D with elevated calprotectin or positive FOBT

— Family history of CRC/IBD

— Failure of empiric therapy with worsening symptoms

Step 3 management: In a 28-year-old woman with classic IBS-D, the correct workup is CBC, CRP, tTG-IgA, fecal calprotectin — not colonoscopy, not abdominal CT, not a food allergy panel. Order, reassure, and start a therapeutic trial.

Guiding principle (ACG 2021): In patients meeting Rome IV criteria without alarm features, do minimal, targeted testing — not a shotgun panel.

Recommended baseline labs for all suspected IBS:

For IBS-D specifically, ACG conditionally recommends:

Tests that are NOT routinely indicated:

Colonoscopy indications in suspected IBS:

Diagnostic Workup — Advanced or Confirmatory Studies

— Gold standard to exclude IBD, microscopic colitis, and CRC

— Random biopsies of normal-appearing mucosa mandatory in chronic watery diarrhea — diagnoses lymphocytic and collagenous colitis (microscopic colitis), which mimics IBS-D especially in women >50 on NSAIDs, PPIs, or SSRIs

— Terminal ileum intubation if Crohn's suspected

— Confirms celiac disease when serology positive or strongly suspected despite negative serology (IgA-deficient patient — use IgG-DGP or IgG-tTG)

— Hydrogen/methane breath test for SIBO — consider in refractory bloating/IBS-M with risk factors (prior abdominal surgery, scleroderma, diabetic gastroparesis, opioid use)

— Methane-positive correlates with constipation; hydrogen-positive with diarrhea

— For refractory IBS-C to identify dyssynergic defecation — treated with biofeedback, not laxatives

— 25–50% of IBS-D have bile acid malabsorption

— Test: 48-hour fecal bile acids, serum C4 (7α-OH-4-cholesten-3-one), or empiric cholestyramine trial

— CT/MR enterography only if Crohn's, stricture, or mass suspected

— Pelvic ultrasound if gynecologic mimics (endometriosis, ovarian pathology)

— Gastric emptying study if gastroparesis features overlap

CCS pearl: On a CCS case with IBS-D and new nocturnal diarrhea, weight loss, or elevated calprotectin, the next correct step is colonoscopy with biopsies — not another empiric drug trial. The clock punishes therapeutic dithering when red flags appear.

When to escalate testing: new alarm features develop, age ≥45, failure of initial empiric therapy after 4–8 weeks, or diagnostic uncertainty.

Colonoscopy:

Upper endoscopy with duodenal biopsy:

Breath testing:

Anorectal manometry + balloon expulsion test:

Bile acid diarrhea evaluation:

Imaging:

Functional testing rarely needed:

Management Logic and First-Line Non-Pharmacologic Care

— Strong therapeutic alliance: validate symptoms, explain gut–brain axis, set realistic expectations (chronic, relapsing, but manageable)

— Symptom diary for 2 weeks identifying food/stress triggers

— Regular sleep, exercise (≥150 min/week), stress management

— Soluble fiber (psyllium 10–20 g/day) — first-line for IBS-C and effective in mixed IBS; avoid insoluble (wheat bran) — worsens bloating

— Limit caffeine, alcohol, carbonated beverages, fatty/spicy foods

— Smaller, more frequent meals

— Fermentable Oligo-, Di-, Mono-saccharides And Polyols restriction

— 3-phase: 4–6 wk elimination → systematic reintroduction → personalization

— ~50–70% symptom improvement; must be dietitian-supervised to avoid nutritional deficits and disordered eating

— Not for long-term strict use — alters microbiome

— Cognitive behavioral therapy (CBT) — targets catastrophizing, visceral hypervigilance

— Gut-directed hypnotherapy — efficacy comparable to low-FODMAP

— Mindfulness-based stress reduction

— Now available via app-based/telehealth platforms (Mahana, Nerva)

— ACG: conditional recommendation against routine use — evidence inconsistent across strains

— If trialed, single-strain or Bifidobacterium-based, ≥4 weeks before judging benefit

— 180–225 mg TID before meals — antispasmodic; effective for global IBS symptoms; can worsen reflux

Board pearl: ACG 2021 strongly recommends soluble fiber, peppermint oil, gut-directed psychotherapy, and a limited-duration low-FODMAP trial as first-line interventions — these often precede or replace pharmacotherapy for mild–moderate IBS.

Foundation of IBS care (apply to ALL subtypes before/with drugs):

Dietary interventions (tier 1):

Low-FODMAP diet (tier 2):

Behavioral therapies (high-yield, ACG strongly recommends):

Probiotics:

Peppermint oil (enteric-coated):

Pharmacotherapy — Subtype-Directed First-Line Drugs

— PEG 3350 17 g daily — improves stool frequency/consistency but not pain (cheap, OTC, first-line)

— Linaclotide (guanylate cyclase-C agonist) 290 µg daily — improves pain AND constipation; SE: diarrhea

— Plecanatide 3 mg daily — similar mechanism, possibly less diarrhea

— Lubiprostone (ClC-2 activator) 8 µg BID — women only for IBS-C; SE: nausea (take with food)

— Tenapanor (NHE3 inhibitor) 50 mg BID — newest agent

— Tegaserod — back on market for women <65 without CV risk; rarely used

— Loperamide 2–4 mg PRN (up to 16 mg/day) — improves stool form/urgency; does not improve pain

— Rifaximin 550 mg TID × 14 days — nonabsorbable antibiotic; one retreatment course allowed; targets SIBO/dysbiosis

— Eluxadoline (mixed µ-agonist/δ-antagonist) 100 mg BID — contraindicated post-cholecystectomy, in pancreatitis, or alcohol use ≥3 drinks/day (sphincter of Oddi spasm risk)

— Alosetron (5-HT3 antagonist) — REMS program; women with severe refractory IBS-D only (risk: ischemic colitis, severe constipation)

— Bile acid sequestrants (cholestyramine, colesevelam) if bile acid diarrhea

— Antispasmodics: dicyclomine, hyoscyamine — PRN before meals; anticholinergic SE limit elderly use

— TCAs (amitriptyline, nortriptyline 10–50 mg qhs) — central neuromodulation; preferred in IBS-D (constipating)

— SSRIs (paroxetine, sertraline) — preferred in IBS-C; treat coexistent anxiety/depression

— SNRIs (duloxetine) — option, especially with comorbid fibromyalgia

Step 3 management: For IBS-D with significant pain, start low-dose amitriptyline 10–25 mg qhs plus loperamide PRN — TCAs slow transit, reduce visceral hypersensitivity, and improve sleep, hitting three targets.

IBS-C (constipation predominant):

IBS-D (diarrhea predominant):

Pain/bloating across subtypes:

Avoid: chronic opioids (narcotic bowel syndrome), chronic stimulant laxative dependency

Expanded Pharmacology and Combination Strategies

— Mild: lifestyle + diet + PRN antispasmodic or loperamide

— Moderate: add subtype-specific agent (linaclotide, rifaximin) + neuromodulator

— Severe/refractory: combination therapy + psychotherapy + GI specialist

— Start low, go slow: amitriptyline 10 mg qhs, titrate by 10 mg every 1–2 weeks to 25–50 mg

— Allow 4–6 weeks before judging efficacy

— Nortriptyline and desipramine have fewer anticholinergic effects — better in elderly

— Counsel: not for depression dose; explain "rewiring nerve signals from gut to brain"

— Check baseline ECG (QTc) if >50 or cardiac disease before TCA

— Combine PEG + secretagogue (linaclotide)

— Add prucalopride (5-HT4 agonist) for chronic idiopathic constipation overlap

— Pelvic floor PT if dyssynergia identified

— Sequence: loperamide → rifaximin → bile acid sequestrant → eluxadoline → alosetron

— Consider ondansetron 4–8 mg PRN (off-label, helps urgency)

— TCAs + SSRIs + tramadol → serotonin syndrome

— Linaclotide contraindicated <2 years old (fatal dehydration risk; rare in adults)

— Rifaximin minimal systemic absorption — safe in renal/hepatic patients; use even in cirrhosis (also treats HE)

— Lubiprostone: pregnancy category C; avoid in pregnancy

— PEG, loperamide, TCAs, peppermint oil, psyllium = cheap, generic

— Linaclotide, plecanatide, eluxadoline, rifaximin = expensive — prior auth often needed; document failure of cheaper agents first

Board pearl: Eluxadoline is contraindicated after cholecystectomy — a favorite distractor. The patient lacks a gallbladder reservoir, so sphincter of Oddi spasm causes pancreatitis. Always confirm gallbladder status before prescribing.

Stepwise approach by severity:

Neuromodulators (central acting) — dosing pearls:

Refractory IBS-C options:

Refractory IBS-D options:

Drug interactions/safety high-yield:

Cost/access considerations:

Special Populations — Elderly and Renal/Hepatic Impairment

— Mandatory colonoscopy

— Evaluate for microscopic colitis (collagenous, lymphocytic) — biopsy normal-appearing colon

— Rule out medication-induced bowel changes (metformin, SSRIs, magnesium, NSAIDs, PPIs)

— Consider ischemic colitis in vasculopaths with postprandial pain + bloody diarrhea

— Diverticular disease, CRC, fecal impaction with overflow diarrhea

— TCAs: anticholinergic load → confusion, urinary retention, falls — Beers criteria flags amitriptyline; prefer nortriptyline at 10 mg or switch to SNRI

— Dicyclomine/hyoscyamine: on Beers list — avoid

— Loperamide: generally safe; high-dose abuse → torsades (counsel)

— Alosetron: ischemic colitis risk increases with age — avoid

— Linaclotide/plecanatide/lubiprostone: safe in elderly; watch for diarrhea-induced dehydration

— Linaclotide, plecanatide: minimally absorbed — no dose adjustment

— Tenapanor: minimal absorption — safe

— Rifaximin: safe; <0.4% absorbed

— Avoid magnesium-containing laxatives in CKD (hypermagnesemia)

— Phosphate enemas contraindicated in CKD (acute phosphate nephropathy)

— Eluxadoline contraindicated in severe hepatic impairment (Child-Pugh C)

— Rifaximin safe and actually beneficial (also prevents HE)

— TCA dosing: reduce, monitor for sedation

— Lubiprostone: dose reduction in moderate–severe hepatic impairment

Key distinction: First-onset "IBS" after age 50 is a red flag, not a Rome IV diagnosis — colonoscopy with biopsies, calprotectin, and celiac serology are mandatory. Anchoring on functional diagnosis here is a classic Step 3 trap.

New IBS-type symptoms in patients ≥50 are NOT IBS until proven otherwise:

Drug pitfalls in elderly:

Renal impairment:

Hepatic impairment:

Polypharmacy review: deprescribe culprits (recent SSRI start? new metformin? PPI? magnesium oxide?) before adding IBS drugs

Special Populations — Pregnancy, Pediatrics, and Post-Infectious IBS

— IBS symptoms may worsen (progesterone slows transit) or improve

— Safe agents:

— Psyllium, methylcellulose (bulk fiber) — first-line

— PEG 3350 — minimal absorption, safe

— Loperamide — generally considered safe; minimal data, use sparingly

— Sucralfate (for dyspepsia overlap)

— Avoid:

— Linaclotide, lubiprostone, plecanatide — limited data; lubiprostone cat C

— Eluxadoline — limited data; avoid

— Misoprostol (PGE1) — abortifacient

— TCAs — relative; paroxetine cat D (cardiac defects)

— Rifaximin: limited human data; weigh risk/benefit

— Behavioral therapies and dietary modification are preferred mainstays

— Rome IV pediatric criteria require ≥4 days/month abdominal pain × ≥2 months

— Common in adolescents, often with anxiety/school avoidance

— Workup: CBC, CRP, celiac serology, stool calprotectin, urinalysis

— Treatment: reassurance, dietary modification, peppermint oil, cognitive behavioral therapy, hypnotherapy — strong evidence base in kids

— Linaclotide approved age ≥6 for functional constipation; contraindicated <2 (lethal in animal models)

— 10–30% risk after bacterial gastroenteritis (Campylobacter, Salmonella, Shigella, E. coli O157, Giardia, C. difficile)

— Risk factors: female, young, severe acute illness, antibiotic exposure, comorbid anxiety

— Usually IBS-D phenotype

— Often resolves within 1–2 years — counsel patients about natural history; reasonable to trial rifaximin

— Hormonal therapy may affect motility; address inclusively

— Same Rome IV criteria apply

Step 3 management: A 32-year-old woman G2P1 at 22 weeks with IBS-C — use psyllium fiber + PEG 3350 + dietary modification. Defer secretagogues. Reassure that symptoms often improve postpartum.

Pregnancy:

Pediatrics:

Post-infectious IBS (PI-IBS):

Transgender/gender-diverse patients:

Complications and Adverse Outcomes

— IBD, colorectal cancer, malabsorption, or increased mortality

— Counseling that IBS does not shorten life and does not progress to cancer is therapeutic

— Work/school absenteeism — second leading cause of work absence after the common cold

— Sleep disruption, sexual dysfunction, social isolation

— High healthcare utilization, repeated ED visits, unnecessary procedures

— Out-of-pocket costs from supplements, elimination diets

— Anxiety, depression, somatic symptom disorder prevalence 40–60%

— Increased suicide risk in severe IBS — screen periodically

— Eating disorders may emerge from restrictive diets (orthorexia, ARFID) — counsel

— Alosetron → ischemic colitis (mandates REMS; black box)

— Eluxadoline → pancreatitis, sphincter of Oddi spasm (especially post-cholecystectomy)

— Loperamide abuse → QT prolongation, torsades, sudden cardiac death (high-dose for opioid effect)

— Chronic stimulant laxative use → cathartic colon, electrolyte derangement

— TCA toxicity → anticholinergic delirium, arrhythmia, lethal in OD

— SSRI → serotonin syndrome with tramadol/triptans; sexual dysfunction

— Linaclotide → diarrhea, dehydration, AKI in elderly

— Strict low-FODMAP long-term → microbiome diversity loss, calcium/fiber deficiency

— Gluten-free without celiac → no benefit, increased cost

— Attributing new symptoms (weight loss, bleeding) to "her IBS" → missed cancer/IBD diagnosis

— Reassess for new red flags at every visit

Board pearl: Loperamide abuse is an emerging Step 3 theme — patients using 50–200 mg/day for euphoria or opioid withdrawal develop QT prolongation, wide-complex tachycardia, and torsades. Counsel on max 16 mg/day and screen in opioid-use-disorder patients.

Direct medical complications (rare — IBS does NOT cause):

Quality-of-life and indirect complications:

Psychiatric comorbidity:

Treatment-related complications:

Dietary complications:

Diagnostic overshadowing:

When to Escalate Care — Referral and Inpatient Triage

— Diagnostic uncertainty or alarm features

— Refractory symptoms despite optimized first-line therapy (8–12 weeks)

— Need for advanced testing (anorectal manometry, bile acid testing, breath testing)

— Suspected microscopic colitis, IBD, celiac, SIBO

— Severe IBS requiring biologics-tier IBS drugs (alosetron, eluxadoline)

— Significant anxiety/depression (PHQ-9 ≥10, GAD-7 ≥10)

— Somatic symptom disorder, history of trauma

— For CBT, gut-directed hypnotherapy, antidepressant management

— Initiating low-FODMAP diet (3-phase guidance)

— Weight loss or signs of disordered eating

— Multiple food restrictions raising deficiency risk

— Severe dehydration from diarrhea unresponsive to oral rehydration

— Acute abdomen, peritoneal signs

— GI bleeding, hematemesis, melena

— Suspected bowel obstruction, perforation, ischemia

— Severe electrolyte derangement (hypokalemia from laxative abuse)

— Treatment toxicity: TCA overdose, loperamide-induced arrhythmia, eluxadoline-induced pancreatitis

— Pelvic floor PT for dyssynergia

— Gynecology for endometriosis overlap

— Urology for interstitial cystitis comorbidity

CCS pearl: A patient with "known IBS" presenting with fever, tachycardia, bloody diarrhea, and elevated CRP is not having an IBS flare — order stool studies, calprotectin, CT abdomen/pelvis, and GI consult. The order set must shift entirely; treating this as IBS will cost you the case.

IBS is overwhelmingly an outpatient diagnosis — admission is essentially never for IBS itself but for reconsideration of diagnosis or treatment complications.

Indications for GI referral:

Indications for behavioral health/psychiatry referral:

Indications for dietitian referral:

Indications for ED evaluation/admission (means rethink the diagnosis):

Subspecialty co-management:

Key Differentials — Same-Category (Functional/GI) Causes

— Bloody diarrhea, nocturnal symptoms, weight loss, fever

— Elevated calprotectin (>250), CRP, ESR; anemia

— Extraintestinal manifestations (uveitis, arthritis, skin)

— Diagnose via colonoscopy + biopsy

— Chronic watery, non-bloody diarrhea, often nocturnal, in women >50

— Triggered by NSAIDs, PPIs, SSRIs

— Colonoscopy: macroscopically normal — diagnosis on biopsy only

— Treat: stop offending drug, budesonide 9 mg/day

— Bloating, diarrhea, weight loss, iron deficiency, dermatitis herpetiformis

— tTG-IgA + total IgA → duodenal biopsy

— 4× more common in IBS-D presentations

— Bloating, diarrhea after specific foods

— Diagnose via dietary trial or breath test

— Bloating, distention, diarrhea or constipation

— Risk factors: prior surgery, scleroderma, gastroparesis, opioid use

— Diagnose via hydrogen/methane breath test; treat with rifaximin

— Post-cholecystectomy or ileal disease

— Diagnose via empiric cholestyramine response or serum C4

— Constipation without pain → not IBS-C

— Dyssynergia: needs manometry, treat with biofeedback

— Steatorrhea, weight loss, postprandial pain; alcohol/tobacco history

— Fecal elastase low; imaging shows ductal/calcific changes

Key distinction: Microscopic colitis is the great IBS-D mimic in women >50 on PPIs/NSAIDs/SSRIs. A "negative colonoscopy" without biopsies misses it. Always order random biopsies in chronic watery diarrhea.

Inflammatory bowel disease (Crohn's, ulcerative colitis):

Microscopic colitis (collagenous, lymphocytic):

Celiac disease:

Lactose/fructose intolerance:

Small intestinal bacterial overgrowth (SIBO):

Bile acid diarrhea:

Chronic constipation (functional, slow-transit, dyssynergic defecation):

Functional dyspepsia, cyclic vomiting syndrome, centrally mediated abdominal pain syndrome — overlap functional disorders

Chronic pancreatitis:

Diverticular disease, post-diverticulitis IBS-like syndrome

Colorectal cancer — always consider in age ≥45 or alarm features

Key Differentials — Other-Category (Systemic/Non-GI) Causes

— Hyperthyroidism — diarrhea, weight loss, tachycardia → check TSH

— Hypothyroidism — constipation, weight gain, cold intolerance

— Diabetes mellitus — gastroparesis, diabetic diarrhea, autonomic neuropathy

— Adrenal insufficiency — abdominal pain, diarrhea, hyperpigmentation, hypotension

— Carcinoid syndrome — flushing, diarrhea → urinary 5-HIAA

— VIPoma, gastrinoma — secretory diarrhea (rare)

— Endometriosis — cyclic pelvic pain, dyschezia, dyspareunia; often misdiagnosed as IBS for years

— Ovarian cyst/torsion, ectopic pregnancy

— Pelvic inflammatory disease

— Ovarian cancer in older women — bloating, early satiety, weight loss

— Interstitial cystitis — pelvic pain, urinary urgency; overlaps with IBS

— Nephrolithiasis (intermittent flank/abdominal pain)

— Giardiasis — chronic diarrhea, malabsorption, weight loss; daycare/travel

— Chronic C. difficile

— Tropical sprue, intestinal TB, parasitic infections in immigrants

— HIV enteropathy

— Metformin, magnesium, colchicine, SSRIs, ACE inhibitors → diarrhea

— Opioids, anticholinergics, iron, calcium, ondansetron → constipation

— NSAIDs → enteropathy

— Bulimia (laxative abuse), anorexia (constipation)

— ARFID, orthorexia from elimination diets

— Colorectal, ovarian, pancreatic, lymphoma

— Chronic mesenteric ischemia — postprandial pain, food fear, weight loss in vasculopath

Board pearl: Endometriosis is misdiagnosed as IBS for an average of 7–10 years in women with cyclic, menses-related abdominal/pelvic pain and dyschezia. Always ask about cyclicity, dyspareunia, infertility — and refer to gynecology when present.

Endocrine:

Gynecologic (key in women with IBS-like pain):

Urologic:

Infectious:

Medication-induced:

Eating disorders:

Malignancy:

Vascular:

Psychiatric: somatic symptom disorder, anxiety, depression

Secondary Prevention and Long-Term Maintenance

— Frame as a chronic relapsing-remitting condition like asthma or migraine

— Patients with strong self-management tools have better outcomes than those passively on drugs

— Use lowest effective dose of subtype-directed drug

— Reassess every 6–12 months — many achieve remission and can taper

— Drug holidays are appropriate when symptoms quiet

— Continue neuromodulators (TCA/SSRI) for at least 6–12 months once effective, then trial taper

— Personalized modified low-FODMAP after reintroduction phase — not lifelong strict elimination

— Maintain soluble fiber, hydration, regular meal pattern

— Periodic dietitian re-touch

— Continued stress management, sleep hygiene, regular exercise

— Booster CBT sessions during flares

— Treat coexistent anxiety/depression — these drive flares

— Don't let IBS label distract from age-appropriate CRC screening starting age 45 (USPSTF)

— Cervical, breast, lung screening per guidelines

— IBS itself does not increase CRC risk — same average-risk screening

— Routine adult immunizations

— Bone health if on chronic restrictive diet — vitamin D, calcium

— IFFGD, GI Society apps and education

— Symptom-tracking apps

— Written action plan: trigger avoidance, rescue meds for flares

— Travel, holidays, menses, stress periods — preemptive strategies

Step 3 management: At the 6-month follow-up of well-controlled IBS-C on linaclotide 290 µg, maintain therapy, reinforce lifestyle, and ensure CRC screening at 45 — do not stop a working drug, but plan a future taper attempt.

There is no "cure" for IBS — goal is durable symptom control and functional restoration:

Maintenance medication strategy:

Diet maintenance:

Psychosocial maintenance:

Cancer screening alignment:

Vaccination/health maintenance:

Patient self-management resources:

Trigger anticipation:

Follow-Up, Monitoring Parameters, and Counseling

— Initial diagnosis: return visit in 4–6 weeks to assess response to first intervention

— Stable on therapy: every 6–12 months

— Drug changes: 4–8 weeks to assess efficacy and tolerability

— Severe IBS: more frequent, often co-managed with GI and behavioral health

— Symptom severity — global IBS Symptom Severity Score, pain frequency/intensity, bowel habit

— Quality of life — work/school, sleep, social

— Mood screening — PHQ-9, GAD-7

— Weight trend — unexplained loss is a red flag, even years into diagnosis

— New alarm features — bleeding, nocturnal symptoms, family history changes

— Medication adherence, side effects, cost barriers

— TCAs: baseline ECG if >50/cardiac disease, periodic ECG with dose escalation

— SSRIs: suicidality (especially in adolescents), sexual side effects

— Alosetron: REMS — ischemic colitis symptoms (bloody diarrhea, severe pain)

— Eluxadoline: pancreatitis symptoms; do not use with alcohol ≥3 drinks/day

— Linaclotide/lubiprostone: diarrhea, dehydration, electrolytes

— Loperamide: counsel max 16 mg/day; QT risk at higher doses

— Validate symptoms; explain gut–brain pathophysiology in plain language

— IBS is chronic but benign — no cancer link, no IBD progression

— Emphasize active self-management, not passive medication consumption

— Set realistic goal: 30–50% improvement, not zero symptoms

— Address fears, shame, healthcare-system frustration

— New red flags any time → reassess

— Symptom phenotype change (IBS-D → IBS-C or vice versa) — consider new etiology

— Failure to respond after multiple optimized therapies — referral

Board pearl: A strong therapeutic relationship — validation, education, continuity — independently improves IBS outcomes as much as any medication. Patients who feel heard have lower healthcare utilization and better symptom scores.

Follow-up cadence:

What to monitor at each visit:

Drug-specific monitoring:

Counseling pillars:

When to recheck workup:

Ethical, Legal, and Patient Safety Considerations

— Once "IBS" is in the chart, future GI complaints risk being dismissed — a safety hazard

— At every visit, explicitly reassess for new red flags; document negative review of alarm features

— Anchoring bias contributes to delayed cancer/IBD diagnoses — a recognized malpractice theme

— Alosetron REMS: patient and prescriber must sign attestation; ischemic colitis risk disclosed

— Eluxadoline: disclose pancreatitis/sphincter of Oddi risk; screen for prior cholecystectomy and alcohol use

— TCAs: discuss off-label use for pain (not depression dose), suicidality, anticholinergic effects

— Patient discharged from hospital with new diarrhea labeled "IBS" without workup — high miss rate for C. diff, IBD, microscopic colitis

— Medication reconciliation: ensure outpatient PCP knows about new neuromodulators (interactions)

— Communicate plan and red flag instructions in writing

— Loperamide abuse for opioid-like effects → cardiac arrhythmias; screen in SUD patients

— Laxative abuse in eating disorders → electrolyte derangement; screen adolescent/young adult women

— Serotonin syndrome when combining TCAs/SSRIs with tramadol, triptans, linezolid, ondansetron

— Anticholinergic burden in elderly → fall risk

— Newer agents (linaclotide, eluxadoline, plecanatide) often unaffordable — document cheaper trials for prior auth

— Behavioral health access limited; telehealth-based gut-directed hypnotherapy expands reach

— Dietitian access varies by insurance — provide free low-FODMAP educational resources

— Severe IBS may qualify for ADA accommodations (restroom access at work/school)

— Document functional impact for FMLA when appropriate

— Do not order IgG food sensitivity panels — no evidence; drives harmful restrictive diets

— Avoid unproven "leaky gut" supplements

Step 3 management: A 25-year-old with IBS-D returns 4 months later with weight loss and rectal bleeding — even with "established IBS," document red flag reassessment and order colonoscopy + labs. Sticking with the prior label is the legal/safety error.

Avoiding diagnostic overshadowing:

Informed consent for advanced therapies:

Transitions of care risks (high-yield Step 3 theme):

Patient safety — drug interactions and abuse:

Health equity and access:

Disability and accommodation:

Avoid harmful pseudo-diagnostics:

High-Yield Associations and Rapid-Fire Clinical Facts

— Pain ≥1 day/week × 3 months, onset ≥6 months prior

— Related to defecation, or change in frequency, or change in form (≥2 of 3)

— Subtypes by Bristol stool scale on symptom days

— F:M = 2:1; peaks in 20s–40s

— 10–12% US prevalence

— Post-infectious IBS in 10–30% after bacterial gastroenteritis

— IBS-C: PEG, linaclotide, plecanatide, lubiprostone, tenapanor

— IBS-D: loperamide, rifaximin, eluxadoline, alosetron, bile acid sequestrants

— Pain: TCA (IBS-D), SSRI (IBS-C), antispasmodics

Board pearl: When a question stem mentions post-cholecystectomy chronic watery diarrhea without other features, the answer is bile acid diarrhea — trial cholestyramine (or colesevelam), not another IBS workup.

Rome IV essentials:

Epidemiology shortcuts:

Comorbid clusters: fibromyalgia, migraine, interstitial cystitis, TMJ, chronic pelvic pain, anxiety, depression, GERD, functional dyspepsia

Workup minimums: CBC, CRP, tTG-IgA + total IgA, fecal calprotectin (especially IBS-D)

Don't order: IgG food panels, routine breath tests, abdominal CT in classic IBS

First-line non-drug: soluble fiber (psyllium), low-FODMAP, peppermint oil, CBT, gut-directed hypnotherapy

First-line drugs by subtype:

Red flags: age ≥50, weight loss, bleeding, anemia, nocturnal symptoms, fever, family history CRC/IBD

Eluxadoline contraindications: no gallbladder, pancreatitis history, alcohol ≥3/day, severe hepatic impairment

Alosetron: REMS, women only, severe IBS-D, ischemic colitis risk

Microscopic colitis triad: chronic watery diarrhea + woman >50 + NSAID/PPI/SSRI use → biopsy

Bile acid diarrhea: post-cholecystectomy IBS-D → cholestyramine trial

Pediatric IBS: CBT and hypnotherapy strongly effective

Pregnancy: psyllium + PEG; avoid secretagogues and eluxadoline

Loperamide max: 16 mg/day; abuse → torsades

CRC screening: start age 45 regardless of IBS diagnosis

IBS does NOT increase risk of CRC, IBD, or mortality

Board Question Stem Patterns

Key distinction: Step 3 stems reward you for not over-testing classic IBS and for immediately escalating when red flags appear — recognize the pivot quickly.

Pattern 1 — Classic IBS diagnosis: 28-year-old woman with 8 months of crampy LLQ pain improving with defecation, alternating stools, bloating, normal exam, normal weight. Next step? → CBC, CRP, tTG-IgA, fecal calprotectin (NOT colonoscopy, NOT abdominal CT).

Pattern 2 — Alarm features: 55-year-old with new "IBS" symptoms, 10-lb weight loss, nocturnal diarrhea, FH of colon cancer. Next step? → Colonoscopy with biopsies.

Pattern 3 — Microscopic colitis trap: 62-year-old woman on omeprazole and naproxen with 6 months of watery, sometimes nocturnal diarrhea; colonoscopy grossly normal. Next step? → Random colonic biopsies (then budesonide if positive; stop NSAID/PPI).

Pattern 4 — Celiac mimic: Young adult with IBS-D, bloating, iron deficiency, dermatitis herpetiformis. Next step? → tTG-IgA with total IgA; if positive, duodenal biopsy.

Pattern 5 — IBS-C first-line: Mild IBS-C with hard stools. Best initial therapy? → Soluble fiber (psyllium) + PEG 3350; reserve linaclotide for inadequate response.

Pattern 6 — IBS-D with pain: Best agent? → Low-dose TCA (amitriptyline 10–25 mg qhs) + loperamide PRN.

Pattern 7 — Eluxadoline trap: 40-year-old post-cholecystectomy with IBS-D. Avoid? → Eluxadoline (pancreatitis risk).

Pattern 8 — Post-infectious IBS: Diarrhea persisting 6 months after Campylobacter. Diagnosis? → Post-infectious IBS-D; trial rifaximin.

Pattern 9 — Bile acid diarrhea: Post-cholecystectomy chronic watery diarrhea. Best trial? → Cholestyramine.

Pattern 10 — Pregnancy: IBS-C in 2nd trimester. Safest? → Psyllium + PEG 3350; avoid secretagogues.

Pattern 11 — Behavioral therapy: Moderate IBS refractory to fiber and dicyclomine. Best evidence-based add-on? → CBT or gut-directed hypnotherapy.

Pattern 12 — Loperamide abuse: Patient with OUD presents with QT prolongation, wide-complex tachycardia. Cause? → High-dose loperamide.

Pattern 13 — Endometriosis: Woman with "IBS" that worsens with menses and dyspareunia. Next step? → Gynecology referral / pelvic exam for endometriosis.

One-Line Recap

Irritable bowel syndrome is a Rome IV-defined disorder of gut–brain interaction diagnosed clinically by recurrent abdominal pain linked to defecation or stool changes — managed with a stepwise combination of dietary modification, soluble fiber, behavioral therapy, and subtype-directed pharmacotherapy, while remaining vigilant for alarm features that should redirect workup toward organic disease.

Board pearl: IBS is the diagnosis where doing less testing but more listening, more education, and more behavioral integration is the right answer — and the diagnosis where missing a red flag pivot is the most punished error on Step 3.

Diagnose positively: Rome IV criteria + absence of red flags + minimal targeted testing (CBC, CRP, tTG-IgA, calprotectin) — colonoscopy only for alarm features or age ≥45.

Treat by subtype: IBS-C with PEG, linaclotide, or plecanatide; IBS-D with loperamide, rifaximin, or eluxadoline (avoid post-cholecystectomy); use TCAs for IBS-D pain and SSRIs for IBS-C pain. Always layer in soluble fiber, low-FODMAP (time-limited), peppermint oil, and CBT/gut-directed hypnotherapy.

Beware mimics: microscopic colitis in older women on NSAIDs/PPIs/SSRIs, celiac in IBS-D, bile acid diarrhea post-cholecystectomy, endometriosis with cyclic pain, IBD with elevated calprotectin, and CRC at age ≥45 — order biopsies when grossly normal colonoscopy.

Long-term care: reassess red flags at every visit, screen mood, maintain CRC screening at 45, use the lowest effective dose, treat psychiatric comorbidity, and frame IBS as a chronic but benign condition where strong therapeutic alliance and self-management drive outcomes as much as drugs.