Dyssynergic defecation

Dyssynergic defecation, also known as spastic pelvic floor syndrome, is a functional disorder characterized by paradoxical contraction or inadequate relaxation of the pelvic floor muscles during defecation, contributing to obstructed defecation syndrome and chronic constipation ¹.

Terminology

Dyssynergic defecation is also known by various other terms such as anismus, anorectal dyssynergy or dyskinetic puborectalis muscle ^2-5.

Epidemiology

Dyssynergic defecation is a common cause of chronic constipation in patients with an evacuation disorder and its prevalence in that particular population has been estimated as high as 27-59% ⁶. Prevalence also increases with advanced age and is more commonly observed in men ^7,8.

Diagnosis

The diagnosis is difficult to establish and is based on a combination of clinical features and a series of diagnostic tests.

Diagnostic criteria

The Rome III expert group defined the criteria for diagnosing dyssynergic defecation based on clinical history, and abnormal results in anorectal manometry, balloon expulsion test, electromyography (EMG) and conventional defecography ^10-12.

Anorectal manometry

Anorectal manometry assesses the rectal sensation, reflexes and compliance. It can exclude the possibility of Hirschsprung disease. During defecation the rectal pressure rises which is synchronized with a relaxation of the external anal sphincter. The inability to coordinate these movements gives rise to dyssynergic defecation. The abnormality in dyssynergic defecation may be due to inadequate pushing force, paradoxical anal sphincter contraction, impaired anal sphincter relaxation or a combination of these mechanisms ¹¹.

Balloon expansion test

This is a functional test, wherein a balloon, filled with warm water, is placed in the rectum. The patient is then asked to expel the balloon. A normal individual can expel a balloon within 1 minute ¹².

Clinical presentation

Patients may present with variable signs and symptoms including ¹³:

• chronic constipation (less than 3 bowel movements per week)

• lengthy excessive straining with hard stool

• anal digitation

• incomplete defecation

• abdominal discomfort

• bloating ¹⁴

Pathology

Dyssynergic defecation is the consequence of a lack of coordination between abdominal, rectoanal and pelvic floor muscles. The failure of rectoanal coordination consists of failure to relax the puborectalis and external anal sphincter muscles or their inappropriate contraction ¹⁵. A significant proportion of patients also have impaired rectal sensation.

Etiology

The precise etiology of dyssynergic defecation is still unclear. It is an acquired disorder, with contributory factors including obstetric injury, sexual or physical abuse, anxiety and psychological stress. In many cases, the cause is not clear.

Radiographic features

Fluoroscopy

Conventional defecography

Evacuation is performed in the sitting position after the insertion of contrast into the patient's rectum. Findings include:

• inadequate opening of the anal canal

• impaired evacuation of contrast

• maintenance of an acute anorectal angle

• rectocele (as a secondary phenomenon)

• anorectal intussusception (as a secondary phenomenon) ^16,17

Magnetic resonance defecography

MR defecography findings include:

• prolonged and incomplete evacuation during defecogram ¹⁸: retention of more than half the amount of rectal contrast is clinically significant ¹⁹

• reduction of anorectal angle during defecation. In normal individuals, the anorectal angle increases more than 20 degrees during evacuation ²⁰

• prominent puborectalis impression over the anorectal junction which results in persistent narrowing and gives a "hourglass-like" appearance ²¹

• diameter of anal canal less than 15 mm during defecation ²²

• pelvic floor descent, rectocele and anorectal intussusception may co-exist with dyssynergic defecation ²³

It is known that the frequency of successful evacuation during proctography is higher with fluoroscopy than with MRI ^26,27, and as such, a lack of evacuation on MRI may prompt an additional fluoroscopy study to ensure that the initial findings were not due to situational anxiety.

Treatment and prognosis

The management protocol for dyssynergic defecation includes ²⁵:

• optimization of stool consistency with advice on dietary intake

• pharmacologic therapy

• biofeedback therapy

• botulinum toxin injection into the puborectalis muscle and external sphincters

• anorectal myomectomy ²⁴

Differential diagnosis

• situational anxiety - the imaging findings, particularly on MRI, may be mimicked by anxiety related to the performance and setting of the study, and as such, offering a follow-up fluoroscopy study and not making the diagnosis solely on imaging grounds are important aspects ²⁵