Constipation

Constipation is a common complaint that refers to the infrequent passage of stool, difficulty passing stool, and/or a sensation of incomplete emptying.

Constipation refers to passing infrequent and/or hard stools, difficulty passing stools (e.g. straining), and/or the feeling of incomplete emptying. It is an extremely common complaint that can occur at any age. It is important to remember that the term is very broad and refers to different difficulties in defaecation.

In general, constipation may occur acutely and resolve or become a chronic problem. Acute constipation is commonly due to medications (e.g. opioids). Chronic describes constipation that has been present for ≥ 3 months duration. The actual cause of constipation may be described as primary or secondary:

• Primary: constipation in the absence of an underlying cause
• Secondary: constipation due to an underlying pathology (e.g. medications, gastrointestinal disorder, endocrine disorder, etc)

Primary constipation is commonly referred to as ‘functional’ or ‘idiopathic’ chronic constipation. Most patients with constipation can be managed with simple lifestyle modification or short-term use of laxatives. Only a small proportion will need more sophisticated assessment and medical management.

It is important to remember that patients with a new change in bowel habit or other concerning ‘red flag’ features (e.g. weight loss, rectal bleeding) need urgent assessment for underlying pathology (e.g. colorectal malignancy, colitis).

Constipation is common and can occur at any age.

In the UK, constipation accounts for a significant proportion of GP consultations, and the overall prevalence is thought to be underestimated due to the number of patients self-treating. It is very common in the elderly and 2-3 times more common in women. In certain groups, constipation is a major problem (e.g. nursing home residents, Parkinson’s disease). It has been estimated that constipation affects ~70% of patients on long stay wards.

Several terms are used to describe subtypes of constipation.

It is important to remember that constipation is a symptom and not a diagnosis in itself. The cause of constipation should be sought and is broadly divided into primary and secondary.

Primary constipation

This refers to constipation without a clear underlying cause. It is broadly referred to as chronic idiopathic constipation or functional constipation. However, it can be divided into different subtypes using symptom-based criteria.

• Normal transit constipation: this refers to infrequent defaecation with evidence of normal colonic transit
• Slow transit constipation: this refers to infrequent defaecation with evidence of slow colonic transit
• Dyssynergic defecation: this refers to an inability to empty the rectum effectively. It is due to paradoxical contraction or inadequate relaxation of pelvic floor muscles during defecation.

The majority of patients with primary constipation have normal transit constipation.

Secondary constipation

This refers to constipation due to an underlying cause. There is a huge list of possible causes. Some of the more common causes are listed below:

• Neurological: Parkinson’s disease, Hirschsprung disease, spinal cord injury, multiple sclerosis
• Metabolic: Hypercalcaemia, diabetes mellitus, hypokalaemia
• Endocrine: Panhypopituitarism, hypothyroidism
• Medications: Iron supplements, antispasmodics, calcium-channel blockers, opiates, tricyclic antidepressants
• Rheumatological: Systemic sclerosis, myotonic dystrophy, amyloid
• Gastrointestinal: Irritable bowel syndrome, colonic strictures, inflammatory bowel disease, rectal prolapse
• Pregnancy

Faecal impaction

The term ‘impaction’ is commonly used to refer to the retention of faeces in the rectum and colon to the extent that spontaneous evacuation is unlikely. It may complicate a primary or secondary cause of constipation. It is usually diagnosed on digital rectal examination or noted on imaging.

The process of defecation is a complex physiological process.

The pathophysiology of constipation is multifactorial as many different mechanisms can contribute to its development. To better understand constipation, it is best to consider it in the context of normal colonic function and defecation.

Normal colonic function

The primary function of the colon is to absorb water and transport waste from the caecum to the rectum for evacuation. Colonic motility is important for the transport of faeces to the rectum where distension initiates the urge to defaecate. Defecation then relies on the coordinated relaxation of the internal anal sphincter and pelvic floor muscles with contraction of the diaphragm and abdominal muscles.

Water absorption

The colon receives about 1.5L of fluid from the small intestines each day with only 200-400 mL being excreted and the rest absorbed. Water reabsorption actively occurs through the reabsorption of sodium. Colonic secretion, which is largely quiescent, is mediated by the cystic fibrosis transmembrane regulator (CFTR).

Colonic motility

There are two types of colonic motility:

• Segmental activity: repetitive non-propulsive contractions that aid mixing and absorption
• Propagated activity: large, coordinated contractions that aid the propulsion of stool from caecum to rectum. Divided into ‘low-amplitude propagated contractions (LAPC)’ and ‘high-amplitude propagated contractions (HAPC)’. LAPCs are frequent, low amplitude, and help transport content in the colon. HAPCs are less frequent, have high amplitude and act as powerful contractions involved in defecation itself.

HAPCs are often seen soon after waking or in relation to specific triggers (e.g. eating, drinking). This association between eating and the urge to defecate is known as the gastrocolic reflex. When stool enters the rectum, it causes distension and the conscious awareness of the urge to defecate. Transport of faeces within the colon normally takes 20-72 hours in adults. The abnormal frequency of HAPCs is thought to play a large role in constipation.

At a molecular level, colonic motility is complex and mediated by various neurotransmitters with 5-hydroxytryptamine (5-HT) being a major factor. Distension of the gut wall by faeces causes the release of 5-HT from enterochromaffin cells that stimulates the local release of neurotransmitters such as acetylcholine that initiates contraction. In addition, inhibitory neurotransmitters such as nitric oxide are released behind the faeces to enable forward movement. Disruption of these neurotransmitters (e.g. 5-HT receptor antagonists, anti-muscarinic) can lead to constipation.

Defecation

Normal faecal continence is maintained because the internal and external anal sphincters remained contracted. In addition, a sling of muscle known as the puborectalis, which is part of the pelvic floor, tethers the rectum forming a tight angle that acts as a barrier to faeces entering the anus.

The initial part of defecation involves rectal filling. This activates receptors in the rectal wall that results in conscious awareness of needing to defecate. A small amount of faeces enters the anal canal by an involuntary relaxation of the internal anal sphincter. This is the rectoanal inhibitory reflex. If it is deemed socially acceptable to defecate, the person will find a toilet and adopt a sitting or squatting position. If not socially acceptable the rectal wall relaxes and the need to defecate subsides temporarily. During defecation, contraction of the abdominal muscles and diaphragm help to exert pressure on the abdominal viscera. At the same time, coordinated relaxation of the external anal sphincter and puborectalis helps to evacuate faeces down the created pressure gradient. After evacuation, there is a closing reflex with regaining external anal sphincter tone.

Disruption of this normal coordinated mechanism can lead to the sensation of incomplete emptying and excessive straining on the toilet. These are collectively known as functional defecation disorders that are felt to be acquired behavioural disorders due to learnt improper toilet techniques. Helpfully, patients can be taught and retrained proper toilet technique. This process is known as biofeedback and is discussed further in management.

Defecation disorders can be further subcategories based on the constellation of symptoms and anorectal physiological tests into:

• Dyssynergic defecation (most common)
• Inadequate defecatory propulsion

Constipation is characterised by infrequent bowel motions, hard lumpy stools, straining, and incomplete emptying.

Infrequent stools are broadly defined as < 3 spontaneous bowel motions per week. This is commonly used as the broad definition for constipation. But remember, constipation is characterised by more than just infrequent bowel motions.

Symptoms

• Infrequent bowel motions
• Hard, lumpy stool
• Straining
• Manually extracting faeces
• Overflow diarrhoea (liquid stool leak around stool)
• Overflow incontinence (loss of control of defecation)
• Feeling incomplete emptying

Signs

A general physical examination may give evidence of a clear secondary cause (e.g. features of hypothyroidism). It is important to examine the abdomen and look at the patients’ general nutritional status. However, it usually does not add much to the diagnosis.

A digital rectal examination is important to exclude a structural problem contributing to constipation (e.g. haemorrhoids, anal stricture, anal mass). A digital rectal examination can also help assess the strength of sphincter function and defecation mechanism by asking the patient to squeeze and subsequently strain during the examination.

Red flags

This refers to a constellation of signs and symptoms that are concerning for a serious underlying condition such as colorectal cancer, anal cancer or inflammatory bowel disease.

• Weight loss
• Rectal bleeding
• Family history of colorectal cancer
• Sudden change in bowel habit
• Abdominal pain
• Iron deficiency anaemia

Patients with red flag clinical features should be referred for urgent assessment. For example, in patients with suspected colorectal cancer, they should be referred on the lower gastrointestinal cancer pathway for assessment within two weeks. NICE outlines excellent guidelines on the referral for suspected lower GI cancers. For more information see our Colorectal cancer note.

The Bristol stool chart is a way of describing the shape and form of faeces.

The use of the Bristol stool chart can provide an objective measure of the form of the patients’ stool.

Stool chart

• Type 1 – Separate hard lumps, like pellets
• Type 2 – Sausage-shaped but lumpy
• Type 3 – Like a sausage but cracks on surface
• Type 4 – Like a sausage, smooth and soft
• Type 5 – Soft blobs, clear-cut edges
• Type 6 – Mushy stool. Fluffy pieces with ragged edges
• Type 7 – Watery, no solid pieces

The diagnosis of chronic idiopathic constipation is based on the Rome IV criteria.

The diagnosis of constipation is usually straightforward based on clinical assessment. Invasive testing or imaging is not required to confirm it. Further investigations may be used if there is a suspected secondary cause of constipation (e.g. bone profile for hypercalcaemia).

A formal diagnosis of primary constipation can be made using the Rome IV criteria. The Rome IV criteria are used to help make the diagnosis of disorders of gut-brain interaction that was previously termed ‘functional gastrointestinal disorders’. This includes chronic idiopathic constipation and defecation disorders (e.g. dyssynergia).

Chronic idiopathic constipation

The Rome IV diagnostic criteria for chronic idiopathic constipation are described below:

• Must include two or more of the following:
  • Straining during more than 25% of defecations
  • Lumpy or hard stools (Bristol Stool Form Scale 1-2) more than 25% of defecations
  • Sensation of incomplete evacuation more than 25% of defecations
  • Sensation of anorectal obstruction/blockage more than 25% of defecations
  • Manual maneuvers to facilitate more than 25% of defecations (e.g., digital evacuation)
  • Fewer than three spontaneous bowel movements per week
  • Loose stools are rarely present without the use of laxatives
  • Insufficient criteria for irritable bowel syndrome

The criteria must be fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis.

Functional defecation disorders (FDD)

FDDs are defined by the Rome IV criteria, which are described below:

• The patient must satisfy diagnostic criteria for chronic idiopathic constipation and/or irritable bowel syndrome with constipation
• During repeated attempts to defecate, there must be features of impaired evacuation, as demonstrated by 2 of the following 3 tests:
  • Abnormal balloon expulsion test
  • Abnormal anorectal evacuation pattern with manometry or anal surface electromyography (EMG)
  • Impaired rectal evacuation by imaging

The criteria must be fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis.

FDDs may be subcategorised as dyssynergic defecation if there is an inappropriate contraction of the pelvic floor as measured with anal surface EMG or manometry with adequate propulsive forces during attempted defecation. The measurement of pelvic floor contraction is done through specialist anorectal physiology testing.

The majority of patients with constipation do not require extensive investigations.

Investigations can be targeted to patients with constipation to exclude secondary causes or when red flag features are present. More specialist investigations may also be used in patients with severe constipation that is refractory to initial therapy.

Stool tests

Basic stool tests may be used if there is a suspicion of inflammatory bowel disease or colorectal cancer, but these are not completed routinely.

• Faecal calprotectin (FCP)
• Quantitative Faecal Immunochemical Test (qFIT)

Bloods

Blood tests may be completed to exclude a secondary cause of constipation (e.g. thyroid function tests) or to look for red-flag features (e.g. anaemia). They are not routinely needed in chronic constipation and should only be completed if a secondary cause is suspected or there is a poor response to treatment.

Examples include:

• Full blood count
• Renal profile
• Bone profile
• HbA1c
• Thyroid function tests
• Specialist: parathyroid hormone, cortisol, electrophoresis

Imaging

Routine imaging is not required for a diagnosis of constipation. Faecal loading due to constipation is commonly observed on abdominal x-rays if completed for other reasons.

Imaging is reserved for patients with a suspected secondary cause of constipation (e.g. diverticular stricture, malignancy). Examples include CT imaging of the abdomen and pelvis or MRI of the pelvis.

Endoscopy

Colonoscopy is often completed for patients with a new change in bowel habit to exclude a serious underlying cause. However, the yield from colonoscopy when the indication is simply chronic constipation is low. Colonoscopy is recommended in patients with red flag features and should follow NICE guidelines. For example:

• Age > 50 with unexplained rectal bleeding
• Age > 50 with rectal bleeding and change in bowel habit
• Age > 60 with change in bowel habits

Specialist investigations

Several specialist tests can be completed in patients with severe, refractory constipation that will be guided by gastroenterologists. These include:

• Colonic transit studies: use of radiopaque markers to assess colonic transit. Different protocols are used to define slow transit
• Wireless motility capsule: ingestion of a wireless capsule to assess regional or whole gut transit time
• Defecography: assesses a patient evacuating barium solution to investigate structural problems contributing to defecatory disorders. A defecatory MRI proctogram is commonly requested
• Anorectal physiology: a series of investigations that can be used to assess sphincter function, rectal sensitivity, propulsive function, pressures (i.e. manometry), and ability to expel a balloon (simple form of defecography)

Most patients can be managed with simple lifestyle modifications or basic laxatives.

It is important to address any secondary factors that have precipitated constipation. For example, avoiding culprit medications or treating electrolyte abnormalities. Patients should be given as much autonomy as possible to self-manage their constipation with lifestyle modifications before moving on to pharmacological therapies.

The general treatment approach should be:

• Lifestyle modifications
• First-line laxatives (osmotic, bulk-forming, softeners)
• Second-line laxatives (stimulants, suppositories and/or enemas)
• Consider biofeedback (defecatory disorders)
• Newer therapies (prokinetics, secretagogues)
• Interventional treatments

Lifestyle modifications

Patients should be advised to eat a healthy diet that is high in whole grains, fruit, and vegetables. In addition, fibre should be slowly increased in the diet to 30 g/day. Increasing too quickly can lead to flatulence and bloating. Maintaining good fluid intake to avoid dehydration is typically advised and patients should take regular exercise.

Basic toilet regimens can also be advised that include:

• Regular, unhurried routine to ensure complete defecation
• Respond immediately to sensation to defecate
• If limited mobility, ensure appropriate access to toilets and privacy
• Provide supported seating if unsteady on toilet

Laxatives

A variety of oral and rectal laxatives can be given to patients to treat constipation. In general, bulk-forming laxatives (e.g. isphagula husk) should be offered first-line with the addition of an osmotic laxative (e.g. macrogol) as needed. Second-line laxatives include stimulants (e.g. Senna) and rectal therapies can be added depending on the underlying cause and symptoms. Bulk-forming laxatives should be avoided in patients with opioid-induced constipation.

The different types of laxatives include:

• Bulk-forming (e.g. fybogel – ispaghula husk, methylcellulose): these work by increasing the ‘bulk’ of the stool that stimulates bowel function. They usually take 2-3 days to work and are usually offered first line. It is important to drink plenty of water alongside bulk laxatives.
• Osmotic (e.g. macrogol, lactulose): these are poorly absorbable molecules that exert an osmotic effect drawing water into the bowel lumen. They are very commonly used laxatives and should be offered after bulk-forming laxatives. They are also very effective in faecal impaction and infrequent bowel motions.
• Stimulant (e.g. senna, bisacodyl, sodium picosulfate): these stimulate the local nervous system within the gut wall that increases colonic contractility and secretions. They work in 6-12 hours. They may be used second-line and better for patients with difficulty emptying rather than infrequent motions.
• Softeners (e.g. arachis oil, sodium docusate): Docusate lowers the surface tension, which leads to water and fats penetrating the stool. They are typically combined with other laxatives (e.g. stimulants).
• Suppositories (e.g. glycerol, bisacodyl): these can be used to aid rectal emptying by stimulating the anal sphincter and initiating peristalsis. Glycerol is an osmotic type laxative and bisacodyl is a stimulant. May be combined with oral laxatives. Commonly used if inadequate response to oral, incomplete emptying, incontinence, or altered rectal sensitivity. Cause more rapid evacuation
• Enemas (e.g. phosphate, sodium citrate, docusate): these include osmotic, softeners, and/or weak stimulants. A phosphate enema contains 128 mL of liquid whereas others are ‘mini-enemas’ that come as only 5 mL. These can be combined with oral laxatives as needed. Like suppositories, they act quickly to bring about a more rapid evacuation.

Newer therapies

Several new therapies can be used in patients. These are typically offered if patients have ongoing constipation despite the use of at least two conventional laxatives from two different classes for at least 6 months. These include:

• Prokinetics (e.g. Prucalopride): Prucalopride is commonly used that works as a selective serotonin 5-HT4 receptor agonist. It simulates mass colonic movement and has an action on other areas of the gastrointestinal tract. It is contraindicated in colonic obstruction and should be used with caution in patients with ischaemic heart disease.
• Secretagogues (e.g. Linaclotide, Lubiprostone): these laxatives work by increasing intestinal chloride secretion that is associated with increased water secretion into the bowel lumen. Linaclotide activates the secretion of chloride through guanylcyclase C which activates CFTR chloride channels. Lubiprostone is derived from prostaglandin E1 and directly activates chloride channels and CFTR. Lubiprostone has been withdrawn in the UK market.
• Opioid-antagonists (e.g. Naloxegol): Naloxegol is a peripherally acting opioid receptor antagonist. It decreases the constipating effects of opioids without altering their central analgesic effects.

Faecal impaction

Patients with faecal impaction should be managed with a typical regimen of high-dose macrogol, which is an osmotic laxative. If there has been an inadequate response then macrogol can be combined with suppositories or enemas. After a few days of an osmotic laxative, or if the stools are soft, a stimulant laxative can be used (it should be avoided if hard stools).

Biofeedback

Anorectal biofeedback is a treatment for patients with constipation related to disordered defecation or those with faecal incontinence. It involves providing the patient with coaching and visual cues to help assist them with isolating and coordinating the pelvic floor muscles during defecation.

Anorectal biofeedback is run by experienced bowel nurse specialists and can be completed with or without the use of anorectal physiology. It essentially helps patients to strengthen or relax the pelvic floor muscles during defecation.

In severe cases, when patients have not responded to simple measures, pharmacological agents, and biofeedback, patients may be trained to use bowel irrigation. Bowel irrigation is well established in patients with colostomies to control stomach output. Trans-anal irrigation can be of benefit in patients with faecal incontinence, structural alteration due to defecation (e.g. rectocele), and constipation. It is a good choice in patients with bowel dysfunction secondary to spinal cord injuries.

Advanced therapies

Surgical intervention is rarely needed for constipation. However, in severe cases surgical intervention may be offered (e.g. subtotal colectomy, segmental colectomy, STARR procedure). The mechanism behind constipation is important to determine. Patients with defecatory disorders need a different surgical approach than those with infrequent bowel motions. It is important to exclude gastrointestinal dysmotility that responds poorly to surgery.