- Clinical science
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 lack of exercise. However, it may be associated with anatomical or physiological colorectal abnormalities (e.g., colorectal carcinoma, motility disorder in diabetic neuropathy). A thorough patient history and examination are essential in making a diagnosis. The patient may complain of hard, painful stools in the event of changed stool consistency (e.g., caused by poor diet or lack of hydration) or difficult, strained passage of soft stool in the event of altered defecatory behavior (e.g., anatomical obstruction, motility disorder). 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 unrelenting constipation. Long-term use of laxatives may result in dependency and paradoxical constipation, which can only be relieved with adequate lifestyle changes.
- Prevalence: ∼ 28% of the general population
- Sex: ♀ > ♂ (3:1)
- Accounts for 3–5% of pediatric outpatient visits
- 30% more common in non-white populations
Epidemiological data refers to the US, unless otherwise specified.
Constipation may be acute or chronic.
Primary (functional): constipation in the absence of an identifiable medical disorder or side effect of medication
- More commonly due to poor diet and insufficient exercise
- In children: typically occurs during weaning, the toilet training phase, or once attending school (because of avoidance of school toilets)
- Secondary: constipation due to a medical disorder or medication
It is important to differentiate between harmless acute constipation and emergency ileus in all age groups!
- Primary (functional) constipation: further subdivided into slow transit constipation (STC), normal transit constipation (NTC), and outlet constipation
|Definition||Additional presenting complaints|
|STC||Prolonged colonic transit time, confirmed on a motility study||Infrequent "urge" to pass stool, abdominal discomfort, bloating|
|NTC||Normal colonic transit time, despite the perception of constipation by the patient (e.g., psychosocial issues)||Abdominal discomfort, bloating|
|Outlet constipation||Lack of coordination (high resistance or low propulsive force) of the pelvic floor muscles during an attempt to pass stool from the rectum||Prolonged straining, rectal discomfort, often difficult passage of soft stool, may require manual maneuvering to evacuate stool|
Primary or secondary causes may change stool consistency, alter defecation habits, or a combination of both.
Mechanism of altered stool consistency
- Primary constipation: Changes in stool consistency are often caused by external factors, such as a lack of exercise or inadequate fluid and fiber intake → slow passage of stool → prolonged absorption of water by the bowel → dry, hard stool → painful defecation → sensation of incomplete and irregular bowel emptying → constipation
- Secondary constipation: very similar to the mechanism to primary constipation; however, slow passage of stool is caused by a structural or biochemical abnormality within the bowels
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 adequate bowel innervation may lead to ineffective peristalsis.
- Ineffective peristalsis → difficult passage of stool regardless of stool consistency (e.g., hard or soft) → sensation of incomplete and irregular bowel emptying
Mechanism of constipation due to anatomical changes
- Anatomical changes within the colon (e.g., , stricture) or rectum (e.g., rectal prolapse) may also cause bowel obstruction and present as constipation.
Constipation is a clinical diagnosis. It requires a detailed patient history, physical examination, and further testing to identify potential underlying conditions and/or alarming features.
- 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's disease), voluntary withholding of stool (e.g., squatting, crying, crossing ankles, hiding), fecal (overflow) incontinence
Rome III diagnostic criteria for adults
At least two of the following symptoms must have occurred in the past 6 months over at least a 12 week period:
Rome III diagnostic criteria for children
At least two of the following symptoms must have occurred over a 1 month period < 4 years OR at least once per week over a 2 month period ≥ 4 years:
Before diagnosing constipation, irritable bowel syndrome (IBS) must be ruled out!
If enough Rome III diagnostic criteria are fulfilled, constipation is possible even when stool is passed regularly!
- Physical examination
- Laboratory investigations: exclude hypokalemia, hypothyroidism, diabetes mellitus
- Imaging: abdominal x-ray
- Colonoscopy: to exclude mechanical obstruction; (e.g., tumor, stenosis) especially in the presence of alarming features (see table below)
|Alarm features in patients with constipation|
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 !
Alarm symptoms and signs in patients with constipation suggest a possible underlying condition!
- IBS with predominant constipation pattern (IBS-C)
The differential diagnoses listed here are not exhaustive.
- Treat any underlying conditions.
Approach for adults
- Begin with lifestyle changes: high-fiber diet; (psyllium seed husk, wheat bran), increased fluid intake; , and exercise
- If constipation continues: administer osmotic laxatives
- Replace with stimulant laxatives if osmotic laxatives are unsuccessful.
- Biofeedback training may be helpful in treating disturbances in defecation.
Approach for children
- 2 weeks–6 months of age, without alarming features
- Children ≥ 6 months of age without suspected organic disease
- Maintenance therapy: laxative therapy (polyethylene glycol or lactulose) until constipation is resolved for at least 1 month (treatment should then be tapered gradually)
- A poor response to the treatments mentioned above or a child < 2 weeks with constipation warrants further investigation to exclude an underlying disorder.
|Mechanism of action||Agent||Characteristics|
|Emollient stool softeners|
|Bulk-forming agents|| |
|Osmotic laxatives|| |
|Stimulative (also 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.
- Opiate-induced constipation: Methylnaltrexone bromide, a peripheral acting opioid receptor antagonist, may be considered when treatment with the laxatives mentioned above does not produce adequate results.
Patients who suffer from severe potassium loss due to laxative therapy may develop hypokalemia, which also reduces bowel motility!
Chronic use of laxatives may lead to drug dependency!