Constipation

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.

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

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)

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:

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. 

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

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.