Anismus

Anismus
Other names	Dyssynergic defecation
Specialty	Gastroenterology

Anismus or dyssynergic defecation is the failure of normal relaxation of pelvic floor muscles during attempted defecation. It can occur in both children and adults, and in both men and women (although it is more common in women). It can be caused by physical defects or it can occur for other reasons or unknown reasons. Anismus that has a behavioral cause could be viewed as having similarities with parcopresis, or psychogenic fecal retention.^{[citation needed]}

Symptoms include

Anismus is usually treated with dietary adjustments, such as dietary fiber supplementation. It can also be treated with a type of biofeedback therapy, during which a sensor probe is inserted into the person's anal canal in order to record the pressures exerted by the pelvic floor muscles. These pressures are visually fed back to the patient via a monitor who can regain the normal coordinated movement of the muscles after a few sessions.

Some researchers have suggested that anismus is an over-diagnosed condition, since the standard investigations or

• Straining to pass fecal material[2]
• Tenesmus (a feeling of incomplete evacuation)^[2]
• Feeling of anorectal obstruction/blockage^[2]
• Digital maneuvers needed to aid defecation^[2]
• Difficulty initiating and completing bowel movements^[3]

Cause

To understand the cause of anismus, an understanding of normal colorectal anatomy and physiology, including the normal defecation mechanism, is helpful. The relevant anatomy includes: the

The rectum is a section of bowel situated just above the anal canal and distal to the sigmoid colon of the large intestine. It is believed to act as a reservoir to store stool until it fills past a certain volume, at which time the defecation reflexes are stimulated.^[4] In healthy individuals, defecation can be temporarily delayed until it is socially acceptable to defecate. In continent individuals, the rectum can expand to a degree to accommodate this function.^{[citation needed]}

The anal canal is the short straight section of bowel between the rectum and the

The point at which the rectum joins the anal canal is known as the anorectal ring, which is at the level that the puborectalis muscle loops around the bowel from in front. This arrangement means that when puborectalis is contracted, it pulls the junction of the rectum and the anal canal forwards, creating an angle in the bowel called the anorectal angle. This angle prevents the movement of stool stored in the rectum moving into the anal canal. It is thought to be responsible for gross continence of solid stool. Some believe the anorectal angle is one of the most important contributors to continence.[5]

Conversely, relaxation of the puborectalis reduces the pull on the junction of the rectum and the anal canal, causing the anorectal angle to straighten out. A

Distension of the rectum normally causes the internal anal sphincter to relax (rectoanal inhibitory response, RAIR) and the external anal sphincter initially to contract (rectoanal excitatory reflex, RAER). The relaxation of the internal anal sphincter is an involuntary response. The external anal sphincter, by contrast, is made up of skeletal (or striated muscle) and is therefore under voluntary control. It can contract vigorously for a short time. Contraction of the external sphincter can defer defecation for a time by pushing stool from the anal canal back into the rectum. Once the voluntary signal to defecate is sent back from the brain, the abdominal muscles contract (straining) causing the intra-abdominal pressure to increase. The pelvic floor is lowered causing the anorectal angle to straighten out from ~90^o to <15^o and the external anal sphincter relaxes. The rectum now contracts and shortens in peristaltic waves, thus forcing fecal material out of the rectum, through the anal canal and out of the anus. The internal and external anal sphincters along with the puborectalis muscle allow the feces to be passed by pulling the anus up over the exiting feces in shortening and contracting actions.^{[citation needed]}

In patients with anismus, the puborectalis and the external anal sphincter muscles fail to relax, with resultant failure of the anorectal angle to straighten out and facilitate evacuation of feces from the rectum. These muscles may even contract when they should relax (paradoxical contraction), and this not only fails to straighten out the anorectal angle, but causes it to become more acute and offer greater obstruction to evacuation.

As these muscles are under voluntary control, the failure of muscular relaxation or paradoxical contraction that is characteristic of anismus can be thought of as either maladaptive behavior or a loss of voluntary control of these muscles. Others claim that puborectalis can become

Anismus could be thought of as the patient "forgetting" how to push correctly, i.e. straining against a contracted pelvic floor, instead of increasing abdominal cavity pressures and lowering pelvic cavity pressures. It may be that this scenario develops due to stress. For example, one study reported that anismus was strongly associated with sexual abuse in women.

In many cases however, the underlying pathophysiology in patients presenting with obstructed defecation cannot be determined.[13]

Some authors have commented that the "puborectalis paradox" and "spastic pelvic floor" concepts have no objective data to support their validity. They state that "new evidence showing that defecation is an integrated process of colonic and rectal emptying suggests that anismus may be much more complex than a simple disorder of the pelvic floor muscles."^[13]

Complications

Persistent failure to fully evacuate stool may lead to retention of a mass of stool in the rectum (fecal loading), which can become hardened, forming a fecal impaction or even fecaliths.^{[citation needed]}

Liquid stool elements may leak around the retained fecal mass, which may lead to paradoxical diarrhoea and/or fecal leakage (usually known as

When anismus occurs in the context of intractable encopresis (as it often does), resolution of anismus may be insufficient to resolve encopresis.^[18] For this reason, and because biofeedback training is invasive, expensive, and labor-intensive, biofeedback training is not recommended for treatment of encopresis with anismus.

The walls of the rectum may become stretched, known as megarectum.^[19]

Diagnosis

In the Rome IV classification, diagnostic criteria for "functional defecation disorders" are as follows:^[20]

• Patient must satisfy diagnostic criteria for functional constipation and/or irritable bowel syndrome with constipation.^[20]
• During repeated attempts to defecate, there must be features of impaired evacuation, as shown by 2 of the following 3 tests:
  • Abnormal balloon expulsion test.^[20]
  • Abnormal anorectal evacuation pattern with manometry or anal surface electromyography.^[20]
  • Impaired rectal evacuation by imaging.^[20]

2 subcategories exist within the functional defecation disorders category:

• Inadequate defecatory propulsive (F3a): Inadequate propulsive forces as measured with manometry with or without inappropriate contraction of the anal sphincter and/or pelvic floor muscles.^[20]
• Dyssynergic defecation (F3b): Inappropriate contraction of the pelvic floor as measured with anal surface EMG or manometry with adequate propulsive forces during attempted defecation.^[20]

For all of these Rome-IV diagnoses, diagnostic criteria must have been fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis.^[20] The subcategories F3a and F3b are defined by age- and gender-appropriate normal values for the technique.^[20]

Previous Rome criteria recommended that anorectal testing is not usually indicated in patients with symptoms until patients have failed conservative treatment (e.g., increased dietary fiber and liquids; elimination of medications with constipating side effects whenever possible).^{[citation needed]}

Definition

Several definitions have been offered:

• According to the International Classification of Diseases (ICD-11): "paradoxical contraction or inadequate relaxation of the pelvic floor muscles during attempted defecation".^[21]
• According to the Rome-IV classification of functional gastrointestinal disorders: "Inappropriate contraction of the pelvic floor as measured with anal surface EMG or manometry with adequate propulsive forces during attempted defecation".^[20]
• According to the American Society of Colon and Rectal Surgeons: "failure of striated muscles of the pelvic floor (puborectalis and external anal sphincter) to relax appropriately during attempted defecation.^[22]
• "Absence of normal relaxation of pelvic floor muscles during defecation, resulting in rectal outlet obstruction".^[23]
• "Malfunction (a
  puborectalis muscle during defecation".^{[citation needed}
  ]
• "[...] failure of [the
  puborectalis] muscle[s] to relax, resulting in maintenance of the anorectal angle and the difficulty with initiating and completing bowel movements".^[3]
• "[...] failure of relaxation (or paradoxic contraction) of the puborectalis muscle sling during defaecation, attempted defaecation or straining."[24]

Digital rectal examination

Physical examination can rule out anismus (by identifying another cause) but is not sufficient to diagnose anismus.

Anorectal manometry

The measurement of

Evacuation proctography

Anismus can be subcategorized into 4 types based on the results of anorectal manometry testing:[22]

• Type 1: The patient can generate and adequate rise in intra-abdominal pressure, yet there is a paradoxical increase in anal sphincter pressures.
• Type 2: The patient is unable to generate an adequate rise in intrarectal pressures and has a paradoxical anal sphincter contraction.
• Type 3: The patient can generate an adequate intraabdominal pressure but either has absent or incomplete (<20%) anal sphincter relaxation.
• Type 4: The patient is unable to generate and adequate pushing force and demonstrates an absent or incomplete sphincter relaxation.

Anismus is classified as a functional defecation disorder. It is also a type of rectal outlet obstruction (a functional outlet obstruction). Where anismus causes constipation, it is an example of

The Rome II classification functional defecation disorders were divided into 3 types,^[25] however the symptoms the patient experiences are identical.^[26]

• Type I: paradoxical contraction of the pelvic floor muscles during attempted defecation
• Type II: inadequate propulsive forces during attempted defecation (inadequate defecatory propulsion)
• Type III: impaired relaxation with adequate propulsion

It can be seen from the above classification that many of the terms that have been used interchangeably with anismus are inappropriately specific and neglect the concept of impaired propulsion. Similarly, some of the definitions that have been offered are also too restrictive.

Rectal cooling test

The rectal cooling test is suggested to differentiate between rectal inertia and impaired relaxation/paradoxical contraction ^[27]

Other techniques include

Treatments for anismus include biofeedback retraining, botox injections, and surgical resection. Anismus sometimes occurs together with other conditions that limit (see contraindication) the choice of treatments. Thus, thorough evaluation is recommended prior to treatment.^[32]

Biofeedback training for treatment of anismus is highly effective and considered the gold standard therapy by many.^[18][33][34] Others however, reported that biofeedback had a limited therapeutic effect.^[35]

Injections of

Historically, the standard treatment was surgical resection of the puborectalis muscle, which sometimes resulted in fecal incontinence. Recently, partial resection (partial division) has been reported to be effective in some cases.^[35][39]

Etymology and synonyms

Paradoxical anal contraction during attempted defecation in constipated patients was first described in a paper in 1985, when the term anismus was first used.

Latin ani - "of the anus"
Latin spasmus - "spasm"

(Derived by extrapolation with the term vaginismus, which in turn is from the Latin vagina - "sheath" + spasmus - "spasm")

Many terms have been used synonymously to refer to this condition, some inappropriately. The term "anismus" has been criticised as it implies a psychogenic cause.^[41] In the most widely accepted classification systems (ICD-11 and Rome-IV, the term "dyssynergic defecation" is preferred.^[21][20] As stated in the Rome II criteria, the term "dyssynergic defecation" is preferred to "pelvic floor dyssynergia" because many patients with dyssynergic defecation do not report sexual or urinary symptoms,^[25] meaning that only the defecation mechanism is affected.

Other synonyms include:

• Dyskinetic puborectalis^[23]
• Puborectalis syndrome^[3]
• Paradoxical puborectalis^[23]
• Nonrelaxing puborectalis^[23]
• Paradoxal puborectal contraction^[8]
• Spastic pelvic floor syndrome,^[42]
• Anal sphincter dyssynergia^[43]
• Paradoxical pelvic floor contraction^[23]

See also

• Defecation postures
• Dystonia
• Parcopresis
• Obstructed defecation syndrome

References