8.2 Lower GI Disorders: Irritable Bowel Syndrome (IBS), Inflammatory Bowel Disease (IBD) & Diverticular Disease

Lower GI Disorders: Irritable Bowel Syndrome (IBS), Inflammatory Bowel Disease (IBD) & Diverticular Disease

Lower gastrointestinal disorders span a continuum from benign functional gastrointestinal disorders (FGIDs) to life-threatening chronic inflammatory bowel diseases and acute surgical emergencies. The Adult-Gerontology Primary Care Nurse Practitioner must demonstrate expert competency in applying standardized diagnostic criteria, recognizing clinical red flags, interpreting non-invasive inflammatory biomarkers, managing advanced immunosuppressive and biologic therapies, and preventing severe complications.

---

1. Irritable Bowel Syndrome (IBS)

Pathophysiology & Brain-Gut Axis Dysregulation

IBS is a disorder of gut-brain interaction characterized by altered gastrointestinal motility, visceral hypersensitivity, impaired intestinal mucosal permeability, low-grade immune activation, and altered gut microbiome composition. Bidirectional signaling between the central nervous system and the enteric nervous system (the brain-gut axis) amplifies visceral pain perception in response to physiological intraluminal distension.

+-----------------------------------------------------------------------------+
|                          ROME IV CRITERIA FOR IBS                           |
|                                                                             |
|   Recurrent abdominal pain on average at least 1 DAY PER WEEK in the last   |
|   3 MONTHS, with symptom onset at least 6 MONTHS prior to diagnosis,        |
|   associated with TWO OR MORE of the following criteria:                    |
|                                                                             |
|   1. Related to DEFECATION (either improvement or worsening of pain).        |
|   2. Associated with a change in the FREQUENCY of stool.                    |
|   3. Associated with a change in the FORM (appearance) of stool             |
|      (evaluated via the Bristol Stool Form Scale).                          |
+-----------------------------------------------------------------------------+

Bristol Stool Form Scale & IBS Subtyping

+-----------------------------------------------------------------------------+
|                        BRISTOL STOOL FORM SCALE (BSFS)                      |
|                                                                             |
|   [Type 1] - Separate hard lumps, like nuts (hard to pass)  --> CONSTIPATION|
|   [Type 2] - Sausage-shaped but lumpy                       --> CONSTIPATION|
|   [Type 3] - Like a sausage with cracks on the surface      --> NORMAL      |
|   [Type 4] - Like a sausage or snake, smooth and soft       --> NORMAL      |
|   [Type 5] - Soft blobs with clear-cut edges                --> DIARRHEA    |
|   [Type 6] - Fluffy pieces with ragged edges, mushy         --> DIARRHEA    |
|   [Type 7] - Watery, no solid pieces; entirely liquid       --> DIARRHEA    |
+-----------------------------------------------------------------------------+

• IBS-C (Constipation Predominant): > 25% of bowel movements are BSFS Type 1 or 2, and < 25% are BSFS Type 6 or 7.
• IBS-D (Diarrhea Predominant): > 25% of bowel movements are BSFS Type 6 or 7, and < 25% are BSFS Type 1 or 2.
• IBS-M (Mixed Bowel Habits): > 25% of bowel movements are Type 1 or 2, AND > 25% are Type 6 or 7.
• IBS-U (Unclassified): Insufficient abnormality of stool consistency to meet criteria for IBS-C, D, or M.

Alarm Features Excluding Simple IBS (Mandating Diagnostic Workup / Colonoscopy)

+-----------------------------------------------------------------------------+
|                   IBS "ALARM FEATURES" (RED FLAGS)                          |
|                                                                             |
|   * Symptom onset at age >= 50 years                                        |
|   * Nocturnal diarrhea awakening patient from sound sleep                    |
|   * Overt rectal bleeding or hematochezia (not attributable to hemorrhoids) |
|   * Unexplained, progressive, unintentional weight loss                     |
|   * Unexplained Iron Deficiency Anemia (IDA) or elevated inflammatory labs  |
|   * Palpable abdominal mass or localized lymphadenopathy                    |
|   * Family history of Colorectal Cancer, IBD, or Celiac Disease in a        |
|     1st-degree relative                                                     |
|   * Progressive, daily, unremitting pain                                    |
+-----------------------------------------------------------------------------+

Diagnostic Strategy & Rational Workup

In a young or middle-aged patient presenting with classic Rome IV criteria and no alarm features, extensive routine testing is unnecessary and discouraged:

1. Routine Labs: Complete Blood Count (CBC) to screen for anemia; C-Reactive Protein (CRP) or Fecal Calprotectin to exclude active mucosal inflammation.
2. Celiac Serology: Tissue Transglutaminase IgA (tTG-IgA) PLUS total serum IgA (to rule out celiac sprue, especially in IBS-D and IBS-M).
3. Stool Studies (in IBS-D): Giardia antigen, routine stool enteric bacterial cultures, and C. difficile PCR if recent antibiotics.

Evidence-Based Treatment Algorithm for IBS

---

2. Inflammatory Bowel Disease (IBD): Crohn's Disease vs. Ulcerative Colitis

Inflammatory Bowel Disease comprises two major chronic, idiopathic, immune-mediated relapsing inflammatory disorders of the gastrointestinal tract: Crohn's Disease (CD) and Ulcerative Colitis (UC).

+-----------------------------------------------------------------------------+
|                   CROHN'S DISEASE vs. ULCERATIVE COLITIS                    |
|                                                                             |
|   FEATURE                 CROHN'S DISEASE (CD)       ULCERATIVE COLITIS (UC)|
|   -----------------------------------------------------------------------   |
|   Anatomical Location     ANY segment from MOUTH     COLON ONLY             |
|                           to ANUS ("Gum to Bum").    Starts at RECTUM and   |
|                           Terminal ileum + cecum     extends proximally in  |
|                           most common (50%).         CONTINUOUS fashion.    |
|                                                                             |
|   Pattern of Lesions      "SKIP LESIONS"             CONTINUOUS, UNBROKEN   |
|                           (patches of normal bowel   mucosal inflammation;  |
|                           between diseased segments). NO skip areas.         |
|                                                                             |
|   Depth of Inflammation   TRANSMURAL (entire wall    MUCOSA and SUBMUCOSA   |
|                           thickness: mucosa to       ONLY (superficial      |
|                           serosa).                   layers).               |
|                                                                             |
|   Endoscopic Appearance   "Cobblestone" appearance,  Continuous erythema,   |
|                           deep linear/serpiginous    loss of vascularity,   |
|                           ulcers, aphthoid ulcers.   friability, pseudo-    |
|                                                      polyps, shallow ulcers.|
|                                                                             |
|   Histopathology          NON-CASEATING GRANULOMAS   CRYPT ABSCESSES, crypt |
|                           (pathognomonic in ~30%),   distortion, absence    |
|                           transmural lymphoid aggregates. of true granulomas.|
|                                                                             |
|   Dominant Clinical Signs Crampy RLQ pain, chronic   BLOODY DIARRHEA with   |
|                           diarrhea (often non-bloody) mucus, severe TENESMUS|
|                           weight loss, low-grade fever fecal urgency, LLQ   |
|                           aphthous oral ulcers.      crampy pain.           |
|                                                                             |
|   Structural Complications STRICTURES (obstruction),  TOXIC MEGACOLON        |
|                           FISTULAS (perianal,        (colonic diameter >6cm)|
|                           enterocutaneous, entero-   Massive hemorrhage,    |
|                           vesical), PERIANAL ABSCESS Colorectal Cancer.     |
|                                                                             |
|   Malabsorption / Deficits Vitamin B12 deficiency     Iron deficiency anemia |
|                           (terminal ileal disease),  due to chronic rectal  |
|                           bile acid diarrhea,        blood loss.            |
|                           gallstones, oxalate stones.                       |
|                                                                             |
|   Serologic Biomarkers    ASCA Positive              p-ANCA Positive        |
|                           (Anti-Saccharomyces)       (Perinuclear ANCA)     |
|                           p-ANCA Negative (usually)  ASCA Negative (usually)|
|                                                                             |
|   Cigarette Smoking Role  SMOKING WORSENS DISEASE    SMOKING IS PROTECTIVE  |
|                           (higher recurrence/surgery)(cessation may flare!) |
|                                                                             |
|   Surgical Role           Non-curative (disease      CURATIVE (Total        |
|                           recurs at anastomoses);    proctocolectomy with   |
|                           reserved for strictures.   ileal pouch-anal IPAA).|
+-----------------------------------------------------------------------------+

Extraintestinal Manifestations (EIMs) of IBD

Extraintestinal manifestations occur in up to 40% of IBD patients and are classified based on whether their clinical activity parallels active bowel inflammation:

+-----------------------------------------------------------------------------+
|                   EXTRAINTESTINAL MANIFESTATIONS (EIMs)                     |
|                                                                             |
|   A. PARALLEL TO BOWEL INFLAMMATION (Improve with GI disease remission):    |
|      1. Peripheral Arthropathy: Non-deforming, asymmetric, large joint      |
|         pauciarticular arthritis (knees, ankles, wrists).                   |
|      2. Erythema Nodosum: Tender, painful, erythematous subcutaneous nodules|
|         typically over the anterior pretibial surfaces.                     |
|      3. Episcleritis: Benign inflammatory injection of episclera; ocular    |
|         redness and irritation without visual loss.                         |
|      4. Aphthous Stomatitis: Recurrent, painful shallow oral ulcers.        |
|                                                                             |
|   B. INDEPENDENT OF BOWEL INFLAMMATION (Run a separate clinical course):    |
|      1. Axial Spondylitis / Sacroiliitis: Ankylosing spondylitis strongly   |
|         associated with HLA-B27; causes progressive spinal stiffening.      |
|      2. Pyoderma Gangrenosum: Severe, rapidly progressive, painful necrotic |
|         ulcerations with purplish/violaceous undermined borders; exhibits   |
|         PATHERGY (worsened by surgical debridement!).                       |
|      3. Anterior Uveitis / Iritis: Deep ocular pain, photophobia, blurred   |
|         vision; represents an ophthalmologic emergency.                     |
|      4. Primary Sclerosing Cholangitis (PSC): Progressive cholestatic       |
|         fibrosing inflammation of bile ducts ("onion-skin" strictures);     |
|         strongly linked to Ulcerative Colitis (70-80%); markedly increases  |
|         risk of Cholangiocarcinoma and Colorectal Cancer!                   |
+-----------------------------------------------------------------------------+

Pharmacotherapy and Biologic Management in IBD

+-----------------------------------------------------------------------------+
|                         IBD THERAPEUTIC PYRAMID                             |
|                                                                             |
|   [LEVEL 1: 5-AMINOSALICYLATES (5-ASAs)]                                    |
|   - Mesalamine (oral and topical suppository/enema), Sulfasalazine.         |
|   - First-line for induction and maintenance of MILD-TO-MODERATE UC.        |
|   - Sulfasalazine requires mandatory FOLIC ACID co-supplementation (1 mg/d).|
|                                                                             |
|   [LEVEL 2: CORTICOSTEROIDS (INDUCTION ONLY)]                               |
|   - Oral Prednisone, IV Methylprednisolone, Oral Budesonide (controlled-    |
|     ileal release formulation with high first-pass hepatic metabolism;      |
|     ideal for mild-to-moderate ileocecal Crohn's disease).                 |
|   - STRICT RULE: Used solely for ACUTE INDUCTION. NEVER for maintenance!    |
|                                                                             |
|   [LEVEL 3: IMMUNOMODULATORS]                                               |
|   - Azathioprine (AZA), 6-Mercaptopurine (6-MP), Methotrexate (for CD).     |
|   - MANDATORY PRE-TREATMENT TESTING: TPMT (Thiopurine Methyltransferase)    |
|     and NUDT15 genotype/phenotype to prevent life-threatening bone marrow   |
|     toxicity and severe leukopenia.                                         |
|                                                                             |
|   [LEVEL 4: BIOLOGICS & TARGETED SMALL MOLECULES]                           |
|   - Anti-TNF Agents: Infliximab (IV), Adalimumab (SC), Certolizumab (SC),    |
|     Golimumab (SC). MANDATORY PRE-SCREENING FOR LATENT TB (QuantiFERON-TB)  |
|     AND HEPATITIS B (HBsAg, Anti-HBc) to avoid fatal reactivation!          |
|   - Anti-Integrin: Vedolizumab (gut-selective alpha4-beta7 blocker).        |
|   - Anti-IL-12/23: Ustekinumab, Risankizumab, Mirikizumab.                  |
|   - JAK Inhibitors: Tofacitinib, Upadacitinib (boxed warning: thrombosis).  |
|   - S1P Modulators: Ozanimod (requires baseline ECG, eye exam for macular   |
|     edema, VZV immunity check).                                             |
+-----------------------------------------------------------------------------+

Colorectal Cancer Surveillance Protocols in IBD

Patients with extensive ulcerative colitis (pancolitis or left-sided colitis) and Crohn's colitis involving >1/3 of the colon have a significantly elevated risk of colorectal cancer due to chronic mucosal inflammation.

• Initial Screening Colonoscopy: Recommended 8 years after symptom onset for all patients with extensive colitis.
• Surveillance Frequency: Every 1 to 3 years using high-definition chromoendoscopy with targeted biopsies.
• Special High-Risk Category: Patients with concurrent Primary Sclerosing Cholangitis (PSC) must begin annual colonoscopic surveillance immediately upon PSC diagnosis, regardless of disease duration.

---

3. Diverticular Disease: Diverticulosis vs. Acute Diverticulitis

Definitions & Pathophysiology

• Diverticulosis: The presence of uninflamed "pseudodiverticula" (false diverticula consisting of mucosal and submucosal herniations through the muscularis propria at weak points where nutrient arteries [vasa recta] penetrate the circular muscle layer). Most commonly located in the sigmoid and descending colon (95% in Western populations) due to high intraluminal pressure and low-fiber dietary patterns.
• Diverticular Hemorrhage: Painless, massive, acute lower gastrointestinal bleeding (hematochezia) caused by mechanical shear stress and rupture of the exposed vasa recta at the neck or dome of a diverticulum. Responsible for 30% to 40% of all major lower GI bleeds. Spontaneously resolves in ~80% of cases.
• Acute Diverticulitis: Acute inflammation and infection of a diverticular sac caused by micro- or macro-perforation of the diverticular wall, resulting in localized pericolic inflammation, phlegmon, abscess, or free peritonitis.

+-----------------------------------------------------------------------------+
|                  DIVERTICULOSIS vs. ACUTE DIVERTICULITIS                    |
|                                                                             |
|   FEATURE                 DIVERTICULOSIS             ACUTE DIVERTICULITIS   |
|   -----------------------------------------------------------------------   |
|   Symptom Profile         Asymptomatic in 85%;       CONSTANT, SEVERE LLQ   |
|                           occasional mild cramping   pain, fever, chills,   |
|                           or painless brisk bleeding nausea, bowel changes  |
|   Physical Exam           Completely normal          LLQ tenderness, mass,  |
|                                                      localized guarding     |
|   Inflammatory Markers    Normal CBC and CRP         Leukocytosis with      |
|                                                      left shift, high CRP   |
|   Diagnostic Test         Incidental on colonoscopy  ABDOMINAL CT WITH      |
|                           or CT imaging              INTRAVENOUS CONTRAST   |
|   Colonoscopy Status      Safe and routine           STRICTLY CONTRAINDICATED|
|                                                      during acute phase!    |
|   Dietary Strategy        HIGH-FIBER (25-35 g/day);  ACUTE: Clear liquids   |
|                           Hydration (No need to      RECOVERY: Advance diet |
|                           avoid seeds/nuts/corn!)    LONG-TERM: High-fiber  |
+-----------------------------------------------------------------------------+

Clinical Presentation of Acute Diverticulitis

• Hallmark Symptoms: Steady, severe, aching pain localized to the Left Lower Quadrant (LLQ) (can present as Right Lower Quadrant pain in Asian populations with cecal/right-sided diverticulosis), low-grade fever (38.0–38.5°C), anorexia, nausea, constipation (50%) or diarrhea (30%), and dysuria/frequency if the inflamed sigmoid abuts the urinary bladder (sympathetic bladder irritability).
• Physical Examination: Tenderness to palpation in the LLQ, possible tender palpable inflammatory mass, voluntary guarding; involuntary rigidity and diffuse rebound tenderness indicate free perforation and generalized peritonitis.

Diagnostic Evaluation & Modified Hinchey Classification

• Diagnostic Modality of Choice: Contrast-Enhanced CT of the Abdomen and Pelvis (Sensitivity > 95%, Specificity > 95%).
  • Characteristic CT Findings: Colonic wall thickening (> 4 mm), pericolic fat stranding, presence of diverticula, intramural or pelvic abscess, extraluminal air, or contrast extravasation.
• Absolute Contraindication: Colonoscopy, flexible sigmoidoscopy, and barium enemas are STRICTLY CONTRAINDICATED during the acute episode due to the high risk of converting a contained microperforation into a catastrophic free peritoneal perforation from intraluminal air insufflation!
• Post-Recovery Colonoscopy Mandate: Schedule a complete diagnostic colonoscopy 6 to 8 weeks after complete resolution of the acute flare to definitively exclude underlying colonic adenocarcinoma (which can mimic diverticulitis on CT in up to 1% to 2% of cases).

+-----------------------------------------------------------------------------+
|                   MODIFIED HINCHEY STAGING & MANAGEMENT                     |
|                                                                             |
|   HINCHEY STAGE          DESCRIPTION               CLINICAL MANAGEMENT      |
|   -----------------------------------------------------------------------   |
|   Stage Ia               Confined pericolic        Outpatient oral abx /    |
|                          phlegmon / inflammation   selective observation    |
|                                                                             |
|   Stage Ib               Confined pericolic        Abscess < 3-4 cm: IV abx |
|                          or mesocolic ABSCESS      Abscess >= 4 cm: CT-guided|
|                                                    percutaneous drainage    |
|                                                                             |
|   Stage II               Pelvic, distant           CT-guided percutaneous   |
|                          intra-abdominal abscess   drainage + IV abx        |
|                                                                             |
|   Stage III              Generalized PURULENT      Emergency surgical       |
|                          peritonitis (ruptured)    laparotomy / Hartmann's  |
|                                                                             |
|   Stage IV               Generalized FECULENT      Emergency surgical       |
|                          peritonitis (feces)       laparotomy + colostomy   |
+-----------------------------------------------------------------------------+

Guideline-Directed Management of Acute Diverticulitis (AGA / ASCRS Guidelines)

1. Uncomplicated Diverticulitis in Immunocompetent Outpatients:

   • Selective Antibiotic Use (AGA Update): In healthy, immunocompetent patients with mild, uncomplicated diverticulitis, robust social support, and no systemic toxic features, a non-antibiotic strategy consisting of a clear liquid diet for 48–72 hours with close 48-hour follow-up is safe and effective.
   • Outpatient Antibiotic Indications: Mandatory for high-risk patients: older adults, immunocompromised status, significant comorbid disease (DM, CKD, cirrhosis), high fever (> 38.5°C), severe leukocytosis, inability to tolerate oral fluids, or failure of conservative management.
   • First-Line Outpatient Oral Antibiotic Regimens (Duration: 7 to 10 days):
     • Monotherapy: Amoxicillin-Clavulanate (Augmentin) 875/125 mg orally twice daily (BID).
     • Combination Therapy: Ciprofloxacin 500 mg orally BID (or Levofloxacin 500 mg daily) PLUS Metronidazole 500 mg orally TID.
     • Alternative for Fluoroquinolone Intolerance: Cefdinir 300 mg BID (or Cefuroxime 500 mg BID) PLUS Metronidazole 500 mg TID; OR Trimethoprim-Sulfamethoxazole (TMP-SMX DS) 1 tab BID PLUS Metronidazole 500 mg TID.

2. Inpatient Hospitalization Indications:

   • Complicated diverticulitis (Hinchey Ib–IV: abscess, perforation, fistula, obstruction).
   • High fever, severe sepsis, hemodynamic instability, diffuse peritonitis.
   • Inability to tolerate oral hydration or medications (intractable nausea/vomiting).
   • Frail geriatric patients, severe immunosuppression (transplant, chemotherapy, high-dose steroids), failed outpatient therapy after 48–72 hours.
   • Inpatient IV Regimens: Piperacillin-Tazobactam (Zosyn) 3.375g IV Q6H; OR Ceftriaxone 2g IV daily + Metronidazole 500mg IV Q8H.