💩 How to Approach Diarrhea and Constipation: A Symptom-Based Strategy from Bowel to Brain

“I’ve been constipated lately…” “Suddenly I can’t stop having diarrhea…”
These are among the most common complaints heard in general practice. But beneath them may lie not only lifestyle and stress factors, but also endocrine, neurological, inflammatory, or even malignant diseases.

Although seemingly simple symptoms, bowel movement disorders challenge us to apply structured interviewing skills, assess psychosocial factors, and explain non-pharmacologic interventions clearly. In this article, let’s develop a practical framework that will help you both in the clinic and in OSCEs—starting with the gut, but thinking systemically.

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✅ What You Will Learn from This Article

• How to classify and differentially diagnose the causes of diarrhea and constipation
• A structured interview and physical exam framework usable for OSCEs and clinical practice
• Key points in non-pharmacologic care and patient education in real-life settings

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🧑‍⚕️ Clinical Vignette (Patient’s Voice)

【Doorway Information】

40-year-old female / Chief Complaint: Alternating constipation and diarrhea
Vital signs: BP 112/72 mmHg, HR 80/min, Temp 36.9°C, SpO₂ 99% (RA)

【Patient’s Words】

“Doctor, I’ve been having problems with my stomach for months now… I get constipated for a while, then suddenly I have diarrhea. Either way, I never feel completely relieved.”

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Now, how should we approach a case like this? Let’s begin by reviewing the fundamental approach to bowel movement abnormalities using structured clinical reasoning.

🤔 Diarrhea and Constipation – Initial Impressions and Basic Strategy

1. Classify by Time Course

• Acute (within a few days) → Think infectious or drug-induced
• Chronic (weeks to months) → Consider functional or organic causes

2. Understand the Pattern

• Is the patient alternating between constipation and diarrhea?
• Is there a sense of incomplete evacuation?

→ These features raise the suspicion for IBS or defecatory disorders.

3. Check for Red Flags

• Nocturnal symptoms, weight loss
• Bloody stool, fever, anemia

→ Always keep inflammatory bowel disease (IBD) and colon cancer in mind when red flags are present.

By separating these into symptom patterns and potential danger signs, we can build a solid foundation for further assessment.

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🧠 From Complaint to Diagnosis: Fact / Problem / Hypothesis

🟢 Fact (Patient’s Story & Observations)

• 40-year-old woman with alternating constipation and diarrhea
• Persistent symptoms for several months
• Sensation of incomplete evacuation
• No red flag symptoms such as fever or bleeding so far
• Stable vital signs

🟠 Problem (Clinical Interpretation)

• Alternating bowel habit
• Chronic course without alarming signs suggests functional disorder
• Sensation of incomplete evacuation → possible disordered defecation
• However, age (40s) warrants exclusion of organic pathology

🔵 Hypothesis (Differential Diagnosis)

🥇 Primary Suspects

• Irritable Bowel Syndrome (IBS)
• Disordered defecation

🥈 Must-Not-Miss

• Colorectal cancer
• Inflammatory Bowel Disease (IBD)
• Endocrine or metabolic disease (thyroid dysfunction, diabetic enteropathy)

🥉 Context-Dependent

• Prolonged post-infectious diarrhea
• Drug-induced (e.g., antibiotics, laxatives)
• Stress-related or psychosomatic conditions

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📌 What More Do We Need to Know?

Category	Key Questions
HPI	When did it start? Stool frequency, consistency, timing (esp. nocturnal symptoms)
PMH / Medications	Thyroid disease, diabetes, IBD history, current/past medications (e.g., laxatives, anticholinergics)
Family History	Colon cancer, IBD in relatives
Social History	Diet, travel, stress level, occupation, lifestyle, alcohol/smoking
Physical Exam	Abdominal exam, rectal exam, skin/joint findings, hydration
Labs & Imaging	Anemia, CRP, TSH, FOBT, stool culture, fecal calprotectin, abdominal X-ray/endoscopy

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📝 Step 1: History Taking – OPQRST + PAM HITS FOSS

When dealing with diarrhea or constipation, a structured history is crucial. Use OPQRST to explore symptom characteristics, and PAM HITS FOSS to gather relevant background and psychosocial factors.

🔹 OPQRST for Symptom Description

• O (Onset): When did it start? Was it sudden or gradual?
• P (Provocation/Palliation): Does anything make it worse or better? Any food or stress triggers?
• Q (Quality): Watery? Sticky? Fatty? Pebble-like?
• R (Region): Any associated abdominal pain? If so, where?
• S (Severity): How much does it affect your daily life?
• T (Timing): Daily pattern? Any nocturnal episodes?

📋 FACCSSITA – A Detailed Framework for Diarrhea

• F (Frequency): How many times per day?
• A (Amount): Large volume (small bowel) vs small volume (colon)
• C (Contents): Mucus? Fat? Blood? Floating stool?
• C (Consistency): Watery, loose, mushy, soft
• S (Start/Stimulus): Triggered by food, dairy, stress?
• S (Stop): Does fasting relieve it? (suggests osmotic diarrhea)
• I (Intermittency): Is this the first episode or recurrent?
• T (Timing): Morning only? Nighttime too?
• A (Associated symptoms): Fever, nausea, cramps?

💡 Tips from FACCSSITA

• Stops with fasting → Osmotic causes
• Present at night → Think organic, not functional (e.g., IBD)
• Greasy, hard-to-flush → Steatorrhea (think pancreas or biliary disease)
• Family members also affected → Infectious enteritis

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🔸 PAM HITS FOSS – Uncovering Background Factors

Category	Focus Areas
P – Past History	Thyroid disease, diabetes, IBD, colon polyps, neurological disorders
A – Allergy	Drug allergies, especially to laxatives or antibiotics
M – Medications	Opioids, iron, anticholinergics, magnesium, antibiotics
H – Hospitalization	Postoperative constipation, prolonged infectious diarrhea
I – Injury	Spinal cord injuries, pelvic trauma
T – Trauma (psychological)	Stress, abuse history, somatic symptom disorder
S – Surgery	GI or pelvic surgery, cesarean section
F – Family History	Colon cancer, IBD, genetic GI conditions
O – OBGYN	Pelvic organ prolapse, childbirth history
S – Sexual History	STI risk, HIV risk, anorectal pain
S – Social History	Diet, exercise, sleep, stress, smoking, alcohol, work/travel

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🩺 Step 2: Physical Examination – Don’t Miss Red Flags

After gathering a detailed history, the physical exam should aim to narrow the differential, assess severity, and screen for systemic signs. Although constipation and diarrhea are gastrointestinal symptoms, they often reflect endocrine, neurologic, or inflammatory diseases, so a full-body observation is essential.

🔍 General Screening – What to Look For

• General appearance: Signs of fatigue, dehydration, or anemia (e.g., pale conjunctiva)
• Skin & nails: Hyperpigmentation (Addison’s), rashes (IBD-related), dry skin or edema
• Joints: Swelling or tenderness (Crohn’s-related arthritis, psoriatic arthritis)
• Neurologic signs: Parkinsonian facies or posture in chronic constipation

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🩻 Abdominal Examination – The Central Focus

• Inspection: Abdominal distension, surgical scars, visible peristalsis
• Auscultation: Increased bowel sounds (e.g., enteritis), decreased sounds (e.g., ileus)
• Palpation: Tenderness (RLQ = appendicitis, LLQ = diverticulitis), guarding, masses
• Percussion: Tympany suggests gas retention; dullness may indicate mass or ascites

In constipated patients, bowel sounds may still be present despite massive stool retention. Percussion helps assess distension accurately.

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🩻 Digital Rectal Examination – Small Procedure, Big Information

• Fecal impaction: Hard stool felt in rectum
• Blood: Bright red or dark, presence on glove
• Masses: Nodular lesions suggesting rectal cancer or polyps
• Anal tone: Evaluate for defecatory dysfunction or anismus

→ This is the first step in distinguishing IBS-C from outlet obstruction type constipation (disordered defecation).

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🛠️ Use of Auxiliary Tools

• Anoscopy: Direct visualization of hemorrhoids, fissures, and rectal bleeding sites
• Fundoscopy: Assess for hypertensive changes or anemia signs (e.g., hemorrhages)
• Tongue depressor: Examine for oral dryness, cheilitis, ulcers (vitamin deficiency, IBD)

Don’t forget: bowel symptoms can reflect systemic illness. Look beyond the abdomen!

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🧪 Step 3: Tests & Imaging – Targeted Based on Hypotheses

Testing should not be routine. Each investigation should be chosen based on a specific clinical question: Is it to confirm a hypothesis? To rule out a dangerous cause? Or to assess severity?

🧪 1. Blood Tests – Looking Beyond the Gut

• Hemoglobin: Rule out anemia due to bleeding or malabsorption (iron/B12)
• CRP / WBC: Signs of infection or inflammation (e.g., IBD)
• Electrolytes (Na, K): Assess dehydration, losses through stool
• TSH, Free T4: Hypo- or hyperthyroidism
• HbA1c, blood glucose: Screen for diabetic autonomic neuropathy

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💩 2. Stool Tests – Infection, Inflammation, Bleeding

• Stool culture: For infectious causes (e.g., Campylobacter, EHEC, Shigella)
• Fecal occult blood test (FOBT): Screen for bleeding lesions
• Fecal calprotectin: Differentiate IBS from IBD
• Fat stain (Sudan stain): If steatorrhea or malabsorption is suspected

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🖼️ 3. Imaging – Visualizing the Pathology

• Abdominal X-ray: Check for fecal loading, bowel dilation, or obstruction
• Ultrasound (POCUS): Assess for ascites, tumors, biliary or pancreatic disease
• Abdominal CT: Use in red flag cases to evaluate ischemic colitis, neoplasms, or inflammation

💡 Tip: When to Use Abdominal X-ray in Constipation

If stool reaches the rectum, use stimulant laxatives (e.g., senna, picosulfate).
If stool is only in the proximal colon, start with osmotic agents (e.g., PEG, Mg).

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🔬 4. Colonoscopy – For Definitive Diagnosis

• Indications: Hematochezia, chronic diarrhea, weight loss, new bowel habit changes (especially age >50)
• Bowel prep instructions:
  • 2 days before: avoid seaweed, mushrooms, fibrous vegetables
  • Day before: light soft meals (e.g., rice porridge), finish by 9 PM
  • Day of: fasting; water and sports drinks allowed
• Laxatives used: PEG (e.g., Moviprep), Mg sulfate-based preps
• Medication adjustment: Stop iron and laxatives 3–5 days prior; manage antiplatelets/anticoagulants case-by-case

💡 Tips for Safe and Effective Colonoscopy Prep

• Diabetic meds: Hold on the day of exam to avoid hypoglycemia
• Antihypertensives: Can be taken with small sips of water
• Post-sedation: No driving or operating machinery; consider arranging an escort
• Check stool color: Clear to light yellow, no solids = ready for scope

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As we’ve seen, tests must be guided by clinical reasoning—not reflex. From dehydration to malignancy, the true cause of diarrhea or constipation lies in the context.

Next, let’s apply what we’ve learned to our original patient case and reflect on how Step 1 to Step 3 would unfold in practice.

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🔁 Case Revisit – Applying Step 1 to Step 3

Now that we’ve structured the basic approach to diarrhea and constipation, let’s return to the initial case and walk through each step as if you were in the clinic.

🟩 Step 1: History Taking (Fact → Problem → Hypothesis)

Doctor: “What brings you in today?”
Patient: “I’ve had ongoing stomach issues for months… Sometimes I’m constipated, then suddenly I have diarrhea. But either way, I never feel completely relieved.”

— This suggests alternating bowel patterns. Chronic course. I need to assess red flags and clarify stool quality.

Doctor: “Can you describe the stool? Watery or mushy? Any blood?”
Patient: “It’s often watery but not a large amount. No blood that I’ve noticed.”

Doctor: “Does it wake you up at night?”
Patient: “No, mostly during the day.”

→ Nocturnal symptoms absent, small volume → IBS still likely, but need to rule out IBD or malignancy.

Doctor: “Any major illnesses or surgeries in the past?”
Patient: “Not really, but I’ve been sedentary with my office job lately.”

Doctor: “Any family history of colon cancer or bowel diseases?”
Patient: “My father had a colon polyp removed in his 50s.”

→ Family history noted. Colonoscopy may be warranted.

Doctor: “Any recent life stress or changes at work?”
Patient: “Yes, I was recently transferred to a new department. It’s been quite stressful.”

→ Stress-related component may be significant. IBS still likely, but need full evaluation.

Fact: Months of alternating constipation and diarrhea, incomplete evacuation, no nocturnal symptoms, family history of polyps
Problem: Chronic alternating bowel habits, no overt red flags, but age and family history relevant
Hypothesis: IBS, disordered defecation, colorectal polyps or IBD

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🟨 Step 2: Physical Examination

• Inspection: No distention, no surgical scars
• Palpation: Mild LLQ tenderness, no guarding
• Auscultation: Slightly increased bowel sounds
• Percussion: Tympanic throughout
• Rectal exam: No stool impaction, no blood, no palpable masses

→ These findings support a functional diagnosis. No red flags seen on physical exam.

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🟥 Step 3: Tests & Imaging

• Blood work: Hb normal, CRP negative, TSH normal, electrolytes normal
• Stool tests: FOBT negative, culture negative, calprotectin normal
• Abdominal X-ray: Stool present in sigmoid colon, not in rectum
• Colonoscopy: No polyps or signs of inflammation

→ Organic diseases excluded. Rectal evacuation issue possible (disordered defecation).

Conclusion: No evidence of organic pathology. Likely IBS or defecation disorder. Consider lifestyle counseling and possibly gastroenterology or psychosomatic medicine referral.

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🏥 When to Refer to a Specialist

📍 Red Flags That Require Referral

• New-onset bowel habit change in age >50
• Hematochezia, occult blood, maroon or black stools
• Weight loss, fever, anemia, nocturnal diarrhea
• Palpable mass in rectal or abdominal exam
• Elevated calprotectin, CRP, or suspicion of IBD
• Neurologic or psychiatric conditions contributing to symptoms

🛠️ What to Do Before Referring

• Basic labs (CBC, CRP, TSH, electrolytes, glucose)
• Stool tests (culture, FOBT, calprotectin)
• Abdominal X-ray (to assess stool distribution)
• Comprehensive history using PAM HITS FOSS
• Document non-drug and drug interventions trialed so far

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🌿 Non-Pharmacologic Care – What You Can Start Today

💩 For Constipation

• Fiber: 20–25g/day (vegetables, fruits, oats, seaweed)
• Hydration: 1.5–2L/day of fluids
• Healthy oils (e.g., olive oil)
• Light aerobic activity (e.g., walking)
• Proper defecation posture (footstool, leaning forward)
• Daily toilet routine, never ignore the urge
• Psychological support (e.g., CBT, mindfulness)

💩 For Diarrhea

• Avoid fatty, dairy, raw, and cold foods during acute episodes
• Try low-FODMAP diet for IBS or chronic diarrhea
• Use oral rehydration salts (ORS) for fluid balance
• Stress-reduction strategies (deep breathing, CBT)
• IBS reassurance tools (e.g., IBS cards, toilet access plan)
• Workplace/school coordination as needed

🧠 Common to Both

• Regulate daily routine (sleep, meals, activity)
• Consider probiotics
• Explain the gut-brain connection: “Your gut has a mind of its own”
• Use food/symptom diary to monitor patterns

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Next, we’ll organize commonly used medications for constipation and diarrhea by class and mechanism — so that you can prescribe with confidence and precision.

💊 Drug Therapy – How to Choose the Right Medication

There are many medications available for constipation and diarrhea. Let’s organize them by mechanism of action to make clinical decisions easier.

💩 For Constipation

▶︎ Osmotic Laxatives – Pull water into the bowel

• Magnesium oxide: Fast-acting; watch for hypermagnesemia in renal impairment
• PEG (polyethylene glycol): Gentle, safe for chronic use (e.g., Movicol, MiraLAX)
• Lactulose: Mild, but may cause gas and bloating

▶︎ Stimulant Laxatives – Directly trigger peristalsis

• Senna, picosulfate: Take at night; risk of cramping or dependence with overuse

▶︎ Secretagogues – Enhance fluid secretion in the gut

• Lubiprostone: May cause nausea; contraindicated in pregnancy
• Linaclotide: For IBS-C; take on empty stomach
• Elobixibat: Regulates bile acid–mediated motility; take before breakfast

▶︎ Others

• Methylnaltrexone: For opioid-induced constipation; peripherally acting

💩 For Diarrhea

▶︎ Anti-motility Agents

• Loperamide: Effective in acute/chronic diarrhea; avoid in infectious cases

▶︎ Gut Modulators

• Trimebutine: Dual-acting; balances constipation or diarrhea in IBS
• Ramosetron: 5-HT₃ antagonist; approved for IBS-D in men in Japan

▶︎ Bile Acid–Related & Antibiotics

• Cholestyramine: For bile acid diarrhea; may cause constipation
• Rifaximin: For SIBO or IBS-D; not covered by insurance in Japan

▶︎ Supportive Agents

• Probiotics: Can be useful for both constipation and diarrhea
• FMT (fecal microbiota transplant): For recurrent C. difficile infection

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📦 Clinical Tips & Pharmacologic Highlights

📌 Commonly Used Meds – Quick Reference

▶︎ PEG (e.g., Movicol)

Mild osmotic agent; safe for long-term use. Less bloating or gas. Ideal for elderly or pediatric patients.

▶︎ Lubiprostone (Amitiza)

Chloride channel activator that increases intestinal secretion. May cause nausea, especially in women. Avoid in pregnancy.

▶︎ Elobixibat (Goofis)

Inhibits bile acid reabsorption. Take before breakfast to align with morning bowel habits. Not effective when taken after meals.

▶︎ Methylnaltrexone (Relistor)

Peripheral μ-opioid receptor antagonist. Relieves OIC (opioid-induced constipation) without affecting central analgesia.

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🤔 Why Is Ramosetron Only Approved for Men?

Ramosetron, a 5-HT₃ antagonist, is effective for IBS-D. However, in Japan, it’s only approved for men due to a slight increase in ischemic colitis risk in women during overseas trials.

Despite this, it’s sometimes used off-label in women after informed consent and careful monitoring.

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🧪 Column – Probiotics, FMT, and Receptors

🥛 Do “Yakult” and Bifidus Help?

These probiotic drinks are approved as “functional foods” in Japan and may relieve mild GI symptoms like bloating or soft stool.

However, their effect on the microbiome is highly individual, and benefits vary. It’s key to set realistic expectations with patients.

💩 What’s FMT (Fecal Microbiota Transplant)?

FMT involves transplanting stool from healthy donors into patients to restore microbiome balance.

• Approved for: recurrent C. difficile infection (CDI)
• Under research: IBS, refractory constipation, autoimmune conditions

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🧠 Key Receptors in GI Disorders – USMLE-Style Integration

• 5-HT₃, 5-HT₄: Pain/diarrhea in IBS-D, motility in IBS-C
• M₃ (muscarinic): Stimulates motility; blocked by anticholinergics → constipation
• D₂ (dopamine): Inhibits GI motility; dopamine agonists → constipation in Parkinson’s
• μ-opioid receptor: Suppresses peristalsis → OIC
• CB₁, CB₂ (cannabinoid): Research targets in chronic GI issues
• GC-C (guanylate cyclase C): Target of linaclotide; also activated by ETEC ST toxin → traveler’s diarrhea
• CFTR Cl⁻ channels: Activated by cholera or ETEC LT toxin → watery diarrhea
• Bile acid receptors (FXR, TGR5): Involved in bile acid diarrhea or cholestasis-related constipation

🗣️ OET Speaking Session – Diarrhea & Constipation

👥 Scenario

You are a doctor in a family medicine clinic. A 40-year-old woman comes in complaining of alternating constipation and diarrhea for the past few months. She says she never feels fully relieved after passing stool.

You suspect Irritable Bowel Syndrome (IBS), but you also want to rule out colorectal cancer or IBD.

🎯 Your Task

• Take a focused history to clarify the nature and duration of symptoms
• Explain the potential diagnoses in a reassuring yet clear way
• Discuss the need for stool tests, bloodwork, or possible colonoscopy
• Provide lifestyle advice and discuss a follow-up plan

💬 Common Patient Cues & Sample Doctor Responses

🧠 Challenging Questions & Sample Responses

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✉️ OET Writing Task – Sample Referral Letter

Today’s Date

Dr. Sarah Mitchell
Gastroenterology Department
Lakeside Medical Center

Re: Ms. Katherine Lee, 40 years old

Dear Dr. Mitchell,

I am referring Ms. Katherine Lee, a 40-year-old woman, for further evaluation of chronic alternating constipation and diarrhea, with a concern for possible IBS versus an underlying organic pathology.

Ms. Lee has been experiencing alternating bowel habits for the past several months, often feeling incomplete evacuation and bloating. There are no red flag symptoms such as weight loss, bleeding, or nocturnal diarrhea. However, she reports a family history of colorectal polyps (her father), and her symptoms have not responded to initial dietary adjustments.

On physical examination, her abdomen was soft with mild tenderness in the lower left quadrant. No masses were palpated. Rectal examination was unremarkable. Blood work, including CBC, CRP, TSH, and electrolytes, was within normal range. Fecal calprotectin and FOBT were both negative. An abdominal X-ray showed stool accumulation in the sigmoid colon.

Given her persistent symptoms and family history, I believe colonoscopic evaluation is warranted to rule out colonic pathology and to assist with a more definitive diagnosis. I would appreciate your assessment and further recommendations regarding long-term management.

Please feel free to contact me for any further information.

Yours sincerely,

Dr. [Your Name]
General Practitioner

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✅ Summary – Key Takeaways from This Article

Constipation and diarrhea are among the most common symptoms in general practice. Yet, they often reflect more than just a local gut issue — they may be the first signs of endocrine, neurologic, or even oncologic conditions.

This article has guided you through a stepwise approach using:

• Structured history-taking (OPQRST + PAM HITS FOSS + FACCSSITA)
• Targeted physical exams (including DRE and systemic clues)
• Selective testing based on red flags and hypotheses
• Pharmacologic and non-pharmacologic strategies tailored to patient needs

We’ve also explored how seemingly minor symptoms might reflect larger systemic processes:

• In Parkinson’s disease, constipation can precede motor symptoms
• Depression and anxiety often manifest with GI symptoms like IBS
• Gut microbiome dysregulation may play a role in autoimmune and metabolic disease

In other words, the bowel can be a window to the brain, the immune system, and beyond.

When facing a patient with diarrhea or constipation, don’t stop at “Take this laxative.” Instead, ask: “Why now? Why this patient?” The answer may reveal more than just a digestive issue — it may unlock a story that spans the whole person.

🔗 Related Articles

• Abdominal Pain – A Practical Symptom-Based Strategy
• Hematemesis/Hematoeczema/Melena – Thinking Systemically in Primary Care
• Abdominal mass – Exploring the Hidden Causes
• 【Japanese Version】便秘・下痢の診かた（症候別アプローチ）

📚 References

1. Japanese Society of Gastroenterology. Guidelines for the Management of Chronic Constipation 2017. Nankodo, 2017.
2. Japan Gastroenterological Endoscopy Society. Manual of Colonoscopy Preparation 2020. Igaku-Shoin, 2020.
3. Otsuka K, et al. “The link between the gut and the brain: implications for GI symptoms in systemic disease.” Jpn Clin Microbiota Forum, 2022.
4. Rome Foundation. Rome IV Diagnostic Criteria for Functional Gastrointestinal Disorders, 2016.
5. Barbara G, Stanghellini V, et al. Gut-brain axis in IBS and psychobiotics. Nat Rev Gastroenterol Hepatol. 2019.
6. Ford AC, et al. Systematic review: efficacy of pharmacological therapies for IBS. Am J Gastroenterol. 2014.
7. Schiller LR. Review article: the therapy of constipation. Aliment Pharmacol Ther. 2001.

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