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Definition and Diagnostic Criteria

Constipation is defined by difficult or infrequent bowel movements (≤3 per week), hard stools, excessive straining, sensation of incomplete evacuation, obstruction, or the need for digital maneuvers in ≥25% of defecations.

The Rome IV criteria distinguish:

Functional constipation (chronic idiopathic constipation, CIC): absence of predominant abdominal pain.

Irritable bowel syndrome with constipation (IBS-C): abdominal pain is the hallmark feature and typically improves after evacuation.

Temporal Classification

Acute constipation: recent onset over days to weeks in a patient with previously normal bowel habits. Always requires evaluation for secondary causes such as medications, obstruction, or acute metabolic/neurologic events.

Chronic constipation: symptoms lasting ≥3 months, typically present for ≥3 of the last 6 months. Subtypes include:

1. Normal transit constipation.

2. Slow transit constipation (colonic inertia, reduced high-amplitude propagated contractions, enteric neuropathy/myopathy).

3. Defecatory disorder / pelvic floor dyssynergia.

Epidemiology and Age Distribution

Children: Most cases are functional. Red flags include delayed passage of meconium, growth failure, congenital malformations, or Hirschsprung disease.

Young adults: Often related to lifestyle (low fiber intake, sedentary behavior, travel, stress).

Older adults: Higher prevalence due to polypharmacy, neurologic comorbidities, and reduced mobility.

Etiology

Primary (functional)

1. Normal transit constipation.

2. Slow transit constipation (colonic inertia, neuropathic or myopathic dysfunction of the enteric system).

3. Dyssynergia (paradoxical anal contraction or inadequate expulsive effort). Biofeedback is the treatment of choice for this phenotype.

Secondary causes

Medications: opioids, anticholinergics, tricyclic antidepressants, iron, calcium channel blockers (verapamil), diuretics (due to dehydration), antihistamines, antipsychotics.

Endocrine/metabolic: hypothyroidism, hypercalcemia, diabetes mellitus.

Neurologic: Parkinson disease, stroke, peripheral neuropathy, spinal cord lesions.

Structural: colorectal cancer, strictures.

Occupational/environmental: restricted bathroom access, chronic dehydration from heat exposure (construction/agriculture), circadian rhythm disruption (night shifts).

Diagnostic Evaluation (stepwise approach)

1. History and medication review, plus abdominal and anorectal examination (digital rectal exam with Valsalva maneuver).

2. Alarm features → colonoscopy or further testing: hematochezia, iron-deficiency anemia, weight loss, abdominal/rectal mass, new onset after age 50, family history of colorectal cancer. In absence of red flags, colonoscopy is not required beyond age-appropriate screening.

3. Laboratory testing: limited; CBC routinely, and targeted tests (TSH, calcium, glucose) if clinically suspected.

4. If initial management fails: evaluate for defecatory disorder with anorectal manometry and balloon expulsion test. Defecography if uncertainty persists.

5. Colonic transit studies:

Radiopaque markers (Sitzmarks®): >20% retained on day 5 suggests slow transit. Segmental vs diffuse pattern provides further guidance.

Wireless motility capsule (SmartPill/WMC): measures pH, temperature, and pressure to assess whole-gut and segmental transit.

Clinical tools: The Bristol Stool Scale (types 1–2 = constipation; types 3–4 = ideal).

Management (stepwise, phenotype-directed)

Universal measures

Dietary fiber: soluble fiber (psyllium) titrated to 25–35 g/day, plus adequate hydration and regular physical activity. Psyllium has stronger evidence than bran or inulin.

Avoid excessive wheat bran if significant bloating is present.

1. Chronic Idiopathic Constipation (without dyssynergia)

First-line: Polyethylene glycol (PEG 3350) 17 g daily (may increase to BID) ± psyllium.

If inadequate response → add or alternate with stimulant laxatives: bisacodyl 5–15 mg nightly; senna 8.6–17.2 mg nightly.

Refractory cases:

Secretagogues: linaclotide 145 mcg daily (72 mcg available), plecanatide 3 mg daily, lubiprostone 24 mcg BID.

Prokinetic (5-HT4 agonist): prucalopride 2 mg daily (1 mg if renal impairment/elderly).

According to AGA–ACG 2023 guidelines, PEG remains the foundation of therapy.

2. Defecatory Disorders (Dyssynergia)

Biofeedback therapy guided by manometry: retrains motor patterns, improves stool frequency and ease of passage, and is superior to laxatives.

Indicated in patients with abnormal balloon expulsion test and anorectal manometry.

3. Slow Transit Constipation

Long-term PEG ± stimulant laxatives are safe.

Secretagogues or prucalopride may be added.

Surgery (subtotal colectomy with ileorectal anastomosis) is reserved for highly selected cases after excluding dyssynergia.

4. Opioid-Induced Constipation (OIC)

First-line: PEG or stimulant laxatives.

If refractory: Peripheral µ-opioid receptor antagonists (PAMORAs):

Naldemedine 0.2 mg daily.

Naloxegol 25 mg daily (12.5 mg if adverse effects).

Methylnaltrexone (SC, weight-based dosing).

Analgesic therapy should be continued if clinically required.

5. Pediatrics (key points)

Disimpaction if fecal impaction is present, followed by PEG maintenance.

Family education, scheduled toileting, and close follow-up are essential.

Referral if red flags or refractory course.

Commonly Used Adult Doses

PEG 3350: 17 g in 240 mL water daily (adjust as needed).

Lactulose: 15–30 mL every 12–24 h.

Magnesium hydroxide: 30–60 mL daily (avoid in CKD).

Magnesium citrate: 150–300 mL single dose (intermittent use).

Bisacodyl: 5–15 mg PO at bedtime or 10 mg suppository.

Senna: 8.6–17.2 mg nightly (titrated).

Glycerin suppository: as needed.

Phosphate enemas: use cautiously in elderly, CKD, or heart failure.

Secretagogues / Prucalopride: as above.

Tenapanor (for IBS-C): 50 mg BID.

Special Considerations

Occupational dehydration (heat, restricted bathroom access): encourage scheduled hydration, morning bowel routine, and portable soluble fiber.

Elderly/frail: review medications; PEG preferred. Avoid magnesium/phosphate salts if renal impairment. Assistive devices and toileting training may help.

Pregnancy/postpartum: prioritize fiber, PEG, and glycerin suppositories; limit stimulant laxatives to intermittent use.

Differentiating from IBS-C: if pain predominates and improves with defecation, manage as IBS (low FODMAP diet, neuromodulation, tenapanor/linaclotide).

Simplified Algorithm

1. No alarm features → soluble fiber + PEG (± stimulant).

2. If inadequate response → evaluate for dyssynergia (ARM + BET).

If dyssynergia → biofeedback.

If not → secretagogue or prucalopride.

3. If opioid-related and refractory → PAMORA.

4. If persistent with documented slow transit → consider advanced therapies (including surgery in rare, selected cases).

Raúl Ayala, MD
Internal Medicine –