Constipation is defined clinically as infrequent (typically <3 per week), difficult, or incomplete defecation. However, since "normal" bowel movement frequency is highly variable among individuals, constipation must be evaluated in the context of the patient’s baseline patterns.

• Functional constipation affects up to 15% of the population, increasing with age and more common in females.

• Alarm symptoms (e.g., hematochezia, weight loss, anemia) may indicate a more serious underlying condition.

Pathophysiology

Mechanisms

1. Delayed colonic transit – Most commonly due to dysfunction in colonic motility (e.g., slow transit constipation).

2. Outlet dysfunction – Includes pelvic floor dyssynergia or rectocele.

3. Secondary constipation – Arises from systemic disease, medications, or structural abnormalities.

Neuroenteric Involvement

• Autonomic Nervous System: Senses rectal distention and coordinates motor responses.

• Enteric Nervous System: Dysregulation may impair peristalsis.

• Psychological factors and voluntary suppression of defecation also influence motility.

Clinical Assessment

History

• Bowel habits: Frequency, consistency (per Bristol stool scale), duration of symptoms, straining, incomplete evacuation.

• Pain: Onset, location, relationship with defecation.

  • Worsened by defecation: Suggests fissures or hemorrhoids.

  • Relieved by defecation: More common in IBS.

• Alarm features: Hematochezia, weight loss, iron-deficiency anemia, family history of colorectal cancer or IBD.

• Dietary assessment: Fiber intake, hydration status, alcohol use.

• Lifestyle: Physical activity, occupational stress, toilet habits.

• Psychosocial factors: Depression, anxiety, abuse history.

• Medication review: Opioids, anticholinergics, antacids, calcium supplements, iron, antidepressants (esp. tricyclics), calcium channel blockers.

• Laxative use: Chronic use can lead to colonic inertia.

• Comorbidities: Diabetes, Parkinson’s, multiple sclerosis, hypothyroidism, spinal cord lesions.

Physical Examination

• General: Hydration status, signs of hypothyroidism or systemic disease.

• Abdomen:

  • Inspection: Distention, surgical scars.

  • Auscultation: Hypoactive or hyperactive bowel sounds.

  • Palpation: Masses, tenderness, organomegaly.

• Rectal Exam:

  • Inspect for hemorrhoids, fissures, prolapse.

  • Digital rectal exam: Anal tone, mass, impaction, blood.

  • Consider balloon expulsion test or anorectal manometry in outlet dysfunction.

Differential diagnosis and etiologies

Mechanical/Anatomical

• Anal fissure: Painful defecation, bleeding, often secondary to hard stools.

• Rectocele, Intussusception, Hirschsprung’s disease (pediatrics)

Inflammatory

• Diverticulitis: LLQ pain, fever, tender mass, alternating constipation/diarrhea.

• Anorectal abscess: Severe localized pain, fever, purulent drainage.

Neurologic

• Parkinson’s disease: Early nonmotor symptom, due to ENS α-synuclein pathology.

• Spinal cord lesions: Accompanied by motor/sensory loss, urinary retention.

• Diabetic autonomic neuropathy: Episodic constipation, orthostatic hypotension, bladder dysfunction.

Metabolic/Endocrine

• Hypothyroidism: Slowed GI motility, fatigue, weight gain.

• Hypercalcemia: Anorexia, polyuria, abdominal pain, mental status changes.

• Hypokalemia, uremia

Vascular

• Mesenteric ischemia: Acute pain out of proportion, later signs include peritonitis, shock.

Obstructive

• Colorectal cancer: Consider in age >50 or with red flags.

• Volvulus, strictures, fecal impaction

Functional

• Irritable Bowel Syndrome (IBS-C): Recurrent abdominal pain related to defecation, altered stool form or frequency, often with mucus and a sense of incomplete evacuation.

Iatrogenic/Pharmacologic Causes

• Opioids: Decrease peristalsis and intestinal secretions (opioid-induced constipation).

• Anticholinergics: Impair smooth muscle function.

• Calcium supplements, aluminum antacids

• Tricyclic antidepressants

• Vinca alkaloids (e.g., vincristine)

• Laxative overuse: Leads to colonic dysmotility.

Table: Medical and Other Causes of constipation with distinguishing features summary.

Diagnostic Evaluation

Laboratory:

• CBC, TSH, serum calcium, electrolytes, glucose

Imaging and procedures:

• Plain abdominal X-ray: Evaluate for fecal loading, obstruction.

• Colonoscopy or sigmoidoscopy: Indicated in patients >45 with new-onset constipation or alarm features.

• Barium enema/CT colonography: Structural evaluation.

• Transit studies (Sitz marker test): Assess colonic motility.

• Anorectal manometry, defecography: Evaluate outlet dysfunction.

Management Principles

Nonpharmacologic

• Diet: High-fiber (20–35g/day), adequate fluid intake (>1.5–2L/day)

• Physical activity: Encourages colonic motility

• Behavioral: Bowel training, timed toilet sitting, avoidance of suppression

• Pelvic floor retraining: Biofeedback for dyssynergic defecation

Pharmacologic

1. Bulk-forming agents: Psyllium, methylcellulose

2. Osmotic laxatives: Polyethylene glycol (PEG), lactulose

3. Stimulant laxatives: Bisacodyl, senna (short-term use)

4. Stool softeners: Docusate (limited evidence)

5. Secretagogues: Lubiprostone, linaclotide for chronic idiopathic constipation or IBS-C

6. Peripherally-acting mu-opioid receptor antagonists (PAMORAs): Naloxegol, methylnaltrexone for opioid-induced constipation

Special Populations

Pediatric considerations

• Infants: Cow’s milk protein, Hirschsprung’s disease, anal stenosis

• Toddlers/School-aged: Functional constipation from toilet avoidance, lack of privacy

• Red flags: Delayed meconium passage (>48 hrs), ribbon stools, FTT, bilious vomiting

Geriatric considerations

• Increased risk due to:

  • Reduced GI motility

  • Polypharmacy

  • Decreased mobility

  • Laxative overuse

• Acute constipation should raise concern for malignancy, obstruction, or medication effect

Patient education and counseling

• Encourage a balanced diet rich in fiber (fruits, vegetables, whole grains)

• Stress the importance of hydration

• Discuss the risks of chronic laxative use

• Address psychosocial stressors

• Promote physical activity and abdominal exercises

• Reinforce the normal variations in bowel frequency

References