Constipation

Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Primary/functional constipation can be divided into normal transit, slow transit, and outlet constipation. Constipation is a symptom, not a disease, and appropriate management requires an evaluation of possible etiologies, such as systemic disorders and drugs. Once secondary causes have been eliminated, idiopathic constipation can be managed with lifestyle modifications and medications.

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Overview

Definition

Constipation is a symptom generally defined as bowel movements < 3 times per week; stools are frequently difficult to pass.

Epidemiology

  • Prevalence: 
    • 15% of the population is affected by chronic constipation
    • Most common digestive complaint in the general population
  • Sex: women > men (3:1)
  • Age: 
    • Prevalence of adult constipation increases with age, especially in those ≥ 65 years
    • Pediatric constipation affects up to 30% of children, most commonly in the preschool age group.
  • Race/ethnicity: 
    • ↑ Prevalence in non-White as compared with White Americans
    • ↑ Prevalence in White as compared with Black Africans
    • Rare overall in Africa and India, where stool weight is 3–4 times greater than in Western countries

Classification

Constipation can be classified as either primary or secondary, as well as by duration (acute or chronic).

  • Primary constipation (also known as idiopathic or functional constipation) is constipation not caused by a medical disorder or medication; it is divided into 3 subtypes:
    • Normal colonic transit constipation:
      • Stool passes through the colon at a normal rate, but patients find it difficult to pass it.
      • Most common subtype
    • Slow colonic transit constipation:
      • Characterized by infrequent bowel movements, ↓ urgency, and/or straining to defecate
      • Impaired phasic colonic motor activity (e.g., no increase in motor activity after meals)
    • Outlet constipation (also known as pelvic floor dyssynergia)
      • Difficulty expelling stool from the anorectum owing to dysfunction of the pelvic floor and/or anal sphincter 
      • Results in prolonged straining, feeling of incomplete evacuation, use of perineal or vaginal pressure during defecation to allow the passage of stool, or digital evacuation of stool
  • Secondary constipation: constipation due to a medical disorder (structural or systemic) or medications
  • Acute constipation: present ≤ 12 weeks
  • Chronic constipation: present > 12 weeks

Etiology

Primary constipation

Primary constipation, also known as functional constipation, is when there are no identifiable medical disorders. Primary constipation may be due to:

  • Habits:
    • Low-fiber diet
    • Inadequate water intake
    • Sedentary lifestyle
    • Overuse of coffee, tea, or alcohol
  • Irritable bowel syndrome (IBS) with constipation
  • Pelvic floor dysfunction

Secondary Constipation

Secondary constipation is constipation due to a medical disorder or medication.

Table: Causes of secondary constipation
EtiologyExamples
Structural causes
  • Anal fissure
  • Painful hemorrhoids
  • Colonic strictures
  • Obstructing tumors/colorectal cancer
  • Volvulus
  • Pelvic floor dysfunction, including:
    • Rectal mucosal prolapse
    • Rectocele
Endocrine and metabolic disorders
  • Hypothyroidism
  • Hypercalcemia
  • Hyperparathyroidism
  • Hypokalemia
  • Diabetes mellitus
  • Pregnancy (states of ↑ estrogen and progesterone)
Neurologic disorders
  • Parkinsonism
  • Multiple sclerosis
  • Spinal cord or head injury
  • Stroke/cerebrovascular accident
  • Diabetic neuropathy
  • Autonomic neuropathy
  • Hirschsprung disease (i.e., aganglionosis)
  • Chagas disease
  • Familial dysautonomia
Psychiatric disorders
  • Depression
  • Eating disorders (especially anorexia nervosa)
Connective tissue disorders
  • Scleroderma
  • Amyloidosis
  • Mixed connective tissue disease
Medications
  • Opioids
  • Metals:
    • Iron
    • Aluminum-containing antacids
  • NSAIDs
  • Anticholinergics
  • Antidepressants
  • Antipsychotics
  • Ca2+ channel blockers

Pathophysiology

The pathophysiology of constipation varies depending on the etiology, but in general, there are 2 primary mechanisms that cause constipation: altered stool consistency and altered bowel motility.

Altered stool consistency

  • Factors that can alter stool consistency:
    • External factors:
      • ↓ Fiber intake
      • ↓ Fluid intake
      • ↓ Exercise
    • Internal factors: changes within the colon or rectum
  • Process by which altered stool consistency leads to constipation:
    • External / internal factors → 
    • Slow passage of stool → 
    • ↑ Absorption of water by bowel mucosa → 
    • Dry, hard stool → 
    • Painful or irregular defecation, sensations of incomplete defecation → constipation 

Altered bowel motility

Altered bowel motility leads to ineffective peristalsis and difficulty passing stool regardless of its consistency, leading to sensations of incomplete and irregular bowel emptying. Altered bowel motility may arise from a number of mechanisms, including:

  • Problems with bowel innervation → ineffective peristalsis; may be due to:
    • Disease or defects in the intrinsic myenteric plexus or extrinsic sympathetic and parasympathetic nerves
    • Central neurologic disorders
  • Endocrinopathies: 
    • Changes in hormone levels (e.g., thyroid hormones, estrogen) → ↓ bowel motility
    • Diabetes mellitus: can result in neuropathies
  • Hypercalcemia and hypokalemia → ↓ the neuromuscular excitability of the smooth muscle cells within the bowel leading to hypotonicity
  • Megacolon and/or megarectum secondary to chronic fecal retention → ↑ rectal compliance and elasticity and ↓ rectal sensation
  • Outlet obstruction prevents effective defecation; may be due to:
    • Rectal prolapse or rectocele
    • Tumors
    • Functional obstruction: failure to relax the puborectalis and external anal sphincter muscles required for defection (i.e., dyssynergic defecation)
  • Drugs: can lead to autonomic outflow dysfunction and abnormal bowel muscle contraction
Pathophysiology of dyssynergic defecation

Pathophysiology of dyssynergic defecation:
EAS: external anal sphincter
IAS: internal anal sphincter

Image by Lecturio.

Clinical Presentation

History and symptoms

Patients may be asymptomatic, or they may present with the following symptoms:

  • Infrequent bowel movements (< 3/week)
  • Stool:
    • Difficult to expel, passed with straining
    • Bristol Stool Scale forms 1 and 2: hard and/or lumpy
  • Pain:
    • Pain with defecation
    • Abdominal pain relieved by defecation
    • Abdominal cramping
    • Low back pain
  • Bloating
  • Rectal bleeding
  • Overflow diarrhea
  • Tenesmus (cramping rectal pain leading to sensations of needing to evacuate the bowels)
The Bristol Stool Scale

The Bristol Stool Scale

Image by Lecturio.

Examination

  • Abdominal distention
  • On anorectal area examination:
    • Possible fissures
    • Possible hemorrhoids
    • An absent anal wink reflex suggests pathology (e.g., sacral nerve injury).
  • Findings consistent with secondary causes of constipation (e.g., abnormal neurologic findings)

Diagnosis

Diagnostic criteria

Constipation is a clinical diagnosis. The Rome IV diagnostic criteria for functional constipation are used in cases with normal transit time.

Criteria:

At least 2 of the following must have occurred in ≥ 25% of defecations during the past 3 months, with the onset of symptoms ≥ 6 months ago:

  • Passage of stool < 3 times/week
  • Passage of hard or lumpy stool (Bristol Stool Scale form 1 or 2)
  • Straining during attempts to defecate
  • Sensation of anorectal obstruction 
  • Sensation of incomplete defecation
  • Using manual maneuvers to evacuate stool
  • Note: There must also be insufficient criteria for IBS

Indications:

Indications for further workup include:

  • A suspected secondary cause of constipation
  • Refractory chronic constipation (3–6 months of failed medical management)
  • ↑ Risk of colon cancer: family history, age
  • Rectal prolapse
  • Other systemic signs of disease: fevers, sepsis, peritoneal signs on exam

Basic workup

  • Anoscopy: 
    • An anoscope is a rigid tube, approximately 10 cm in length, that allows for direct visualization of the anal canal and distal rectum.
    • Anoscopy is an office procedure that allows for the assessment of anal fissures, ulcers, hemorrhoids, and local anorectal malignancy.
  • Colonoscopy: 
    • Endoscopic procedure allowing for direct visualization of the colon; used to rule out malignancy and/or obtain biopsy samples
    • Indicated in patients at high risk for or with symptoms concerning for colon cancer (e.g., rectal bleeding, weight loss, or anemia)
  • Laboratory: Laboratory evaluation does not play a large role in the initial assessment, but basic studies may provide insight.
    • CBC:
      • WBC for infection
      • Hemoglobin for anemia from GI bleeding
    • CMP:
      • Calcium for parathyroid disorders and hypercalcemia
      • Glucose for diabetes
      • Potassium for hypokalemia
    • Thyroid-stimulating hormone (TSH) for hypothyroidism
    • Fecal occult blood test for blood in stool, which raises concern for cancer
  • Imaging studies: used to evaluate for intra-abdominal or systemic problems; may show significant stool burden in the colon
    • X-ray
    • CT

Motility studies

  • Colonic transit study:
    • For patients in whom colonic motility disorders are suspected
    • Orally administered radiopaque markers are tracked by daily abdominal X-rays. 
    • The colonic transit time is the time it takes for these markers to arrive at the site where they appear to be retained. 
      • In outlet obstruction, markers are retained in the left colon and sigmoid.
      • In colonic dysmotility, the markers may be retained throughout the colon.
  • Anorectal manometry: 
    • Assesses rectal sensation, reflexes, tone, and compliance
    • For patients in whom dyssynergic, myopathic, or neuropathic motility issues are suspected
    • Consider in patients who have primary constipation not responding to fiber supplementation and a trial of osmotic laxatives
  • Balloon expulsion test:
    • A physiologic assessment that can help differentiate between dyssynergia and slow transit constipation
    • Simple office test: A balloon filled with water is inserted into the rectum and the patient is asked to expel the balloon. 
    • A positive test (i.e., failure to expel the balloon) is suggestive, but not diagnostic, of pelvic dyssynergia. 
Measurement of colonic transit time based on radiopaque markers in a patient with chronic idiopathic constipation

Measurement of colonic transit time based on radiopaque markers in a patient with chronic idiopathic constipation:
The plain abdominal X-ray is divided into three segments and the radiopaque markers in each segment are counted.

Image: “Measurement of colonic transit time based on radio opaque markers in patients with chronic idiopathic constipation; a cross-sectional study” by Saberi H, Asefi N, Keshvari A, Agah S, Arabi M, Asefi H. License: CCBY 3.0

Management

The 1st step in management should be to identify and treat any causes of secondary constipation. Next, management should focus on lifestyle changes and use of bulk-forming agents, followed by osmotic laxatives, adding surface-acting agents, and finally using stimulant laxatives.

Initial management

  • Lifestyle changes:
    • ↑ Fiber: goal is > 20–35 g/day 
    • ↑ Fluid
    • ↓ Constipating agents, such as dairy products, coffee, tea, and alcohol
    • ↑ Exercise
    • Attempt to defecate after meals
    • Avoid overusing laxatives
  • Bulk-forming agents (best option for long-term management of constipation)
  • Osmotic agents if needed 
  • Manual disimpaction for fecal impaction
  • Consider:
    • Transrectal enemas, lubricants, and suppositories 
    • Surface agents/surfactants

Secondary management

If initial management is inadequate, additional options are available, including:

  • Biofeedback training for patients with defecatory dysfunction
  • Stimulant laxatives:
    • Daily use of stimulant laxatives may lead to hypokalemia, protein-losing enteropathy, and salt depletion
    • Try to avoid when treating chronic constipation
  • Chloride channel activators
  • Prokinetics
  • Guanylate cyclase C (GC-C) agonists

Pharmacologic options

Table: Medical management of constipation
ClassMechanismIndicationsExamples
Suppositories Liquifies stool Defecatory dysfunction and/or obstruction
  • Glycerin suppository
  • Bisacodyl suppository
Enemas and lubricants Soften stool and provide lubrication Fecal impaction or acute constipation
  • Saline enema
  • Phosphate enema
  • Warm water enema
  • Mineral oil enema
Bulk-forming agents Retain water within the stool and increase fecal mass Mild to moderate constipation; best option for long-term management
  • Psyllium husk
  • Methylcellulose
  • Wheat dextrin
Osmotic agents Poorly absorbed sugars remain in the lumen and lead to water retention in the stool Chronic idiopathic constipation with inadequate response to lifestyle changes and bulk-forming agents (effective in 2‒3 days) 
  • PEG
  • Lactulose
  • Sorbitol
  • Magnesium salts 
  • Glycerin
  • Lacticol
Surface-agents Lower the surface tension of stool leading to increased water and fat within stool Short-term prophylaxis (e.g., postoperative care)
  • Docusate
Stimulant laxatives Alter electrolyte transport of the intestinal mucosa and increase intestinal motor activity Severe constipation not controlled with other treatments (effective in 24 hours)
  • Castor oil
  • Senna
  • Bisacodyl
Chloride channel activators Leads to water and chloride secretion into the stool Opioid-induced constipation
  • Lubiprostone
Prokinetics Serotonin 5-HT4 receptor agonists For severe constipation in patients ≥ 65 years old, not controlled with other treatments
  • Prucalopride
  • Tegaserod
GC-C agonists Induces cGMP, which leads to increased water and electrolyte secretion into the lumen
  • For chronic idiopathic constipation
  • Linaclotide is also used for IBS constipation in adult
  • Linaclotide
  • Plecanatide
5-HT4: 5-hydroxytryptamine receptor 4
PEG: polyethylene glycol

Complications

  • Anal fissures: 
    • Passage of hard, lumpy stools causes a tear in the anoderm.
    • Leads to painful defecation and rectal bleeding
  • Hemorrhoids: 
    • Due to excessive straining with hard, lumpy stools
    • Leads to rectal pain, itching, and/or bleeding
  • Fecal impaction:
    • Obstruction of the rectum with stool
    • Leads to inability to defecate for days or weeks and a tender, distended abdomen
    • Patients may feel the urge to defecate but are unable to do so.
    • Management: manual disimpaction → osmotic enema → stimulatory suppository
  • Fecal incontinence (involuntary defecation):
    • Chronic constipation → formation of a hard stool mass → progressive distention of the anal sphincter complex → patient no longer feels urge to defecate
    • Soft or liquid stool begins to seep around the obstructing stool mass, causing overflow incontinence
  • Urinary retention
  • Pelvic floor damage in women
  • Syncope with straining
  • Megacolon (see Differential Diagnosis)

Differential Diagnosis

  • Appendicitis: acute inflammation of the appendix: Symptoms of appendicitis are periumbilical pain that migrates to the RLQ, fever, anorexia, nausea, and vomiting, but appendicitis can often cause constipation, as well. The diagnosis is clinical, but imaging is used in cases of uncertainty. The standard management is appendectomy, though there can be a role for antibiotics in some cases.
  • Colorectal cancer: 2nd leading cause of cancer-related deaths in the United States. Almost all cases are adenocarcinoma, and the majority of lesions come from the malignant transformation of an adenomatous polyp. Most cases are asymptomatic, so screening colonoscopy or stool tests are recommended in patients ≥ 50 years of age. Diagnosis is by colonoscopy. Management is based on characteristics of the cancer and usually includes surgery and potentially chemotherapy and/or radiation.
  • Large bowel obstruction: interruption in the normal flow of intestinal contents through the colon and rectum. The obstruction may be mechanical (due to actual physical occlusion of the lumen) or functional (due to loss of normal peristalsis, also known as pseudo-obstruction). The typical symptoms include intermittent lower abdominal pain, abdominal distention, and obstipation. Diagnosis is by imaging. Surgery is needed in the majority of cases.
  • Crohn’s disease: chronic, recurrent condition that causes patchy transmural inflammation that can involve any part of the GI tract. The terminal ileum and proximal colon are usually affected. Crohn’s disease typically presents with intermittent, nonbloody diarrhea and crampy abdominal pain. Diagnosis is by endoscopy. Management is with corticosteroids, azathioprine, antibiotics, and anti–tumor necrosis factor (TNF) agents (infliximab and adalimumab).
  • Irritable bowel syndrome: functional bowel disease characterized by chronic abdominal pain and altered bowel habits without an identifiable organic cause. The etiology and pathophysiology of IBS are not well understood, and there are many factors that may contribute. Irritable bowel syndrome is a diagnosis of exclusion, and organic causes should be ruled out. Dietary modifications and symptom control measures may be instituted.
  • Megacolon: severe, abnormal dilatation of the colon classified as acute or chronic. There are many etiologies for megacolon, including neuropathic and dysmotility conditions, severe infections, ischemia, and inflammatory bowel disease. Common symptoms include abdominal distention, pain, bloody diarrhea, and obstipation. Management for acute megacolon includes supportive care, decompression, and, potentially, surgery.

References

  1. Wald A. (2020). Etiology and evaluation of chronic constipation in adults. UpToDate. Retrieved April 22, 2021, from: https://www.uptodate.com/contents/etiology-and-evaluation-of-chronic-constipation-in-adults
  2. Wald A. (2020). Management of chronic constipation in adults. UpToDate. Retrieved April 22, 2021, from: https://www.uptodate.com/contents/management-of-chronic-constipation-in-adults
  3. Basson M. (2020). Constipation. Emedicine. https://emedicine.medscape.com/article/184704-overview
  4. Singh G, Lingala V, Wang H, et al. (2007). Use of health care resources and cost of care for adults with constipation. Clin Gastroenterol Hepatol 5:1053.

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