• Clinical science

Constipation

Summary

Constipation is the infrequent, difficult passage of stool with the sensation of incomplete bowel emptying. It is a common condition in all age groups and often occurs without a pathological cause as a result of a low-fiber diet, poor hydration, and/or a lack of exercise. However, it may be also associated with anatomical or physiological colorectal abnormalities (e.g., colorectal carcinoma, motility disorder in diabetic neuropathy). In the context of constipation, hard, painful stools typically indicate a nutritional cause (e.g., poor diet or lack of hydration), while the difficult, strained passage of soft stool may indicate an organic cause (e.g., anatomical obstruction, motility disorder). Any identifiable underlying cause should be managed accordingly. In the absence of organic disease, constipation may resolve with regular exercise, hydration, and fiber supplementation. Osmotic or secretory laxatives may be considered in patients with persisting constipation. Long-term use of laxatives may result in dependency and paradoxical constipation, which can only be relieved with adequate lifestyle changes.

Epidemiology

  • Prevalence: ∼ 14% of the general population experiences chronic constipation [1]
  • Sex: > (3:1) [2]
  • Accounts for 3–5% of pediatric outpatient visits [3]
  • 30% more common in non-white populations [2]

Epidemiological data refers to the US, unless otherwise specified.

Classification

  • By course: acute or chronic
  • By etiology
    • Primary (functional): constipation in the absence of an identifiable medical disorder
    • Secondary: constipation due to a medical disorder or medication [4]

Acute-onset constipation should raise suspicion of bowel obstruction!

Etiology

References:[3][4][2]

Pathophysiology

Both primary and secondary constipation may cause changes in stool consistency and defecation habits.

  • Mechanism of altered stool consistency
    • External factors such as lack of exercise or inadequate fluid and fiber intake (primary constipation)/internal factors such as changes within the colon or rectum (secondary constipation) → slow passage of stool → prolonged absorption of water by the bowel → dry, hard stool → painful defecation → sensation of incomplete and irregular bowel emptying → constipation.
  • Mechanism of altered bowel motility
    • Effective peristalsis of the bowel is controlled by intrinsic (e.g., myenteric plexus) and extrinsic (e.g., sympathetic and parasympathetic) innervation.
    • Any alteration in bowel innervation may lead to ineffective peristalsis.
      • Drugs (e.g., calcium channel blockers, opiates, antispasmodics, antidepressants) [5] altered autonomic outflow and bowel muscle contraction [6]
      • Endocrine pathology (e.g., hypothyroidism) → downregulated bowel motility
      • Neurological pathology (e.g., spinal injury, enteric neuropathy) → disease or trauma of bowel innervation
    • Ineffective peristalsis difficult passage of stool regardless of stool consistency → sensation of incomplete and irregular bowel emptying

References:[7][3][5][6]

Diagnostics

Constipation is a clinical diagnosis. Identifying potential underlying conditions and/or alarming features requires a detailed patient history, physical examination, and further testing.

Patient history

  • Ask about dietary habits, medication use, mobility, stool character and frequency, problems with defecation, and anorectal pain.
  • Additionally in children: delayed passage of meconium (e.g., Hirschsprung disease), voluntary withholding of stool (e.g., squatting, crying, crossing ankles, hiding), fecal (overflow) incontinence

Rome IV diagnostic criteria for functional constipation in adults

At least two of the following must have occurred in ≥ 1/4 of defecations during the past 12 weeks with onset of symptoms ≥ 6 months ago:

  • Passage of stool < 3 times/week
  • Passage of hard or lumpy stool
  • Sensation of anorectal obstruction/blockage
  • Manual aid to evacuate stool
  • Straining during attempts to defecate
  • Sensation of incomplete evacuation


Physical examination

  • Inspect the anorectal area
  • Digital examination of the rectum

Additional investigations

  • Laboratory investigations: exclude hypokalemia, hypothyroidism, diabetes mellitus
  • Imaging: abdominal x-ray [2]
  • Colonoscopy: to exclude mechanical obstruction; (e.g., tumor, stenosis) especially in the presence of alarming features (see table below) [5][4][2]

Alarming features in patients with constipation

Children

Adults
  • Delayed passage of meconium > 48 hours
  • Constipation when < 1 month old
  • Family history of disorders that may cause constipation (e.g., Hirschsprung disease)
  • Bilious vomiting
  • Severe abdominal distention
  • Blood in stool
  • Fever
  • Failure to thrive
  • Possible congenital abnormalities detected on examination (e.g., tuft of hair on spine, sacral dimple, abnormal position of anus)

A reduced stool caliber (i.e. pencil-shaped stool) and rectal bleeding in a patient > 40 years of age must be further investigated, as these features may be a sign of colorectal cancer!

References:[9][3][4][8][2][5][10]

Treatment

  • Diagnose and treat any underlying conditions.
  • Approach in adults
  • Approach in children [9][3]
    • Infants 2 weeks–6 months of age, without alarming features
      • May only require reassurance
        • Passage of stool is particularly variable in breastfed infants.
        • Parents who formula feed their children should be properly educated on correct formula preparation.
      • Reassess in 2–4 weeks [9]
      • If constipation persists, consider drug therapy (best initial: polyethylene glycol).
    • Children ≥ 6 months of age without suspected organic disease
      • Prompt laxative therapy (best initial: polyethylene glycol)
      • In combination with age-appropriate fiber, fluid, and physical activity requirements
      • Toilet training, if applicable [11]
    • Maintenance therapy: laxative therapy (polyethylene glycol or lactulose) until constipation is resolved for at least 1 month (treatment should then be tapered gradually) [9]
    • A poor response to the treatments mentioned above or a child < 2 weeks with constipation warrants further investigation to exclude an underlying disorder.
Laxatives
Agents Mechanism of action Adverse effects
Emollient stool softener
  • Emulsification (i.e., integration of water and fat) of stool → softening of stool → easier passage through the intestinal tract
Bulk-forming laxatives
  • Bulk-forming laxatives are indigestible, not systemically absorbed → stool bulking due to increased water absorption in the intestinal lumen → stretching of the bowel wall → stimulation of peristalsis
  • Bloating
  • Incorrect usage can result in constipation becoming worse or, in extreme cases, ileus.
Osmotic laxatives
  • Drawing water into the intestinal lumen → stimulating intestinal motility
Stimulant laxatives/secretory laxatives
  • Patients may become dependent on laxatives with prolonged use.
    • Long-term use of OTC laxatives may cause water and electrolyte imbalances in the bowel, paradoxically resulting in further constipation.
    • Adequate lifestyle changes are the only way to break this cycle of constipation.

Patients with severe potassium loss due to laxative therapy may develop hypokalemia, which further reduces bowel motility!

Chronic use of laxatives may lead to dependency!

References:[9][3][11][12][13]

Complications

References:[2]

We list the most important complications. The selection is not exhaustive.