Dyssynergic defecation (DD) is a common functional disorder characterized by difficulty passing stool, affecting up to one-third of people with chronic constipation. This condition is caused by a failure in muscle coordination during a bowel movement, not a physical blockage or lack of fiber. The muscles that should relax to allow stool to pass instead contract or tighten, creating an obstruction at the exit. Because the difficulty is mechanical, DD is often misdiagnosed as standard constipation, leading to ineffective treatment with laxatives alone.
The Mechanics of Normal vs. Dyssynergic Defecation
Normal defecation requires a synchronized effort between the abdominal muscles and the pelvic floor muscles. When the urge to defecate occurs, a person increases pressure in the abdomen to propel the stool downward. Simultaneously, the pelvic floor muscles, specifically the puborectalis muscle and the external anal sphincter, must relax and open. This relaxation straightens the anorectal angle, which is normally held at a sharp curve to maintain continence, allowing for smooth evacuation of the stool.
Dyssynergic defecation, also known as pelvic floor dyssynergia, is a breakdown in this precise coordination. Instead of relaxing, the pelvic floor muscles and the external anal sphincter contract or fail to relax when the person attempts to push. This paradoxical contraction prevents the anorectal angle from straightening and effectively closes the exit, making the effort to pass stool ineffective. The feeling is similar to trying to accelerate a car while simultaneously pressing the brake pedal.
This uncoordinated pattern leads to excessive straining, a sensation of incomplete evacuation, and often the need for manual maneuvers to assist the passage of stool. The continued, unsuccessful straining can also lead to other issues, such as hemorrhoids or rectal prolapse. Physiologically, this condition is classified into subtypes based on whether the anal sphincter pressure increases or fails to decrease adequately during the attempted bowel movement.
Common Causes and Contributing Factors
The precise origin of dyssynergic defecation is not fully understood, but it is primarily considered an acquired behavioral disorder. It is often a learned response that develops over time, frequently stemming from chronic straining or habitually ignoring the urge to defecate. These poor toilet habits can inadvertently lead to an inappropriate muscle tension pattern that disrupts normal coordination.
Specific life events and chronic conditions can also contribute to the development of this disorder. Physical trauma, such as back injuries or injuries sustained during childbirth, can alter the function of the pelvic floor muscles. Certain neurological conditions and the chronic use of opioids are also recognized factors that can affect the nerve and muscle signaling required for proper defecation. Psychological factors like stress and anxiety may play a role by increasing overall muscle tension in the pelvic area.
How Dyssynergic Defecation is Diagnosed
Diagnosing dyssynergic defecation requires specialized tests, as symptoms alone are insufficient to distinguish it from other forms of constipation. A careful digital rectal examination (DRE) is often the first step, where a clinician assesses the strength and relaxation of the anal muscles during a simulated pushing effort. While a DRE can raise suspicion for the disorder, it is not definitive on its own.
The gold standard for diagnosis involves physiological tests to confirm muscle incoordination. Anorectal manometry uses a thin probe inserted into the rectum to measure the pressures exerted by the anal muscles during rest and simulated defecation. This test identifies the dyssynergic pattern by demonstrating a paradoxical increase in anal sphincter pressure or inadequate relaxation when the patient attempts to push.
The Balloon Expulsion Test (BET) is another important tool, which assesses the patient’s ability to evacuate a simulated stool. A small balloon, typically filled with 50 milliliters of water, is placed in the rectum, and the patient is asked to expel it. A prolonged expulsion time, usually exceeding one minute, strongly suggests a defecatory disorder. Together, the manometry and balloon expulsion results provide objective evidence necessary to confirm the diagnosis of dyssynergic defecation.
Primary Treatment Strategies
Traditional treatments for constipation, such as increasing fiber or using osmotic laxatives, often prove ineffective for dyssynergic defecation because the problem is mechanical. The primary treatment is Biofeedback Therapy, a type of neuromuscular training. Biofeedback is a non-invasive process that helps patients re-learn the correct muscle coordination pattern.
During the sessions, specialized equipment, often using pressure sensors or electromyography, provides the patient with real-time visual or auditory feedback on their pelvic floor muscle activity. This immediate feedback allows the patient to consciously identify and correct the paradoxical contraction, learning to relax the puborectalis muscle and external anal sphincter while increasing abdominal pressure. The therapy is typically conducted over several sessions with a specialized physical therapist.
Biofeedback has been shown to be superior to laxatives for correcting the underlying physiological abnormality. In addition to the training, adjunctive measures are often recommended, including dietary modifications to ensure adequate fiber and hydration, and instruction on proper toileting posture. The goal is to restore a normal, coordinated pattern of evacuation and improve the patient’s long-term bowel satisfaction.