Dyssynergic defecation is a common cause of chronic constipation stemming from a functional rather than a structural problem. This condition is characterized by a failure in the coordination of the pelvic floor and abdominal muscles during an attempt to pass stool. Affecting up to 50% of individuals with chronic constipation, it is often overlooked or misdiagnosed. This leads to ineffective treatment with standard laxatives, which do not address the underlying muscular issue. Understanding the malfunction, specialized tests, and targeted therapies is the first step toward effective management.
Understanding the Muscle Dysfunction
Normal defecation is a highly coordinated sequence involving the relaxation of the pelvic floor muscles combined with an increase in abdominal pressure to propel the stool. Specifically, the puborectalis muscle, which acts like a sling around the rectum, and the external anal sphincter must relax and lengthen to straighten the anorectal angle and allow for unimpeded passage. This synchronized relaxation is the normal pattern for successful evacuation.
In contrast, dyssynergic defecation involves a failure of this crucial coordination, often resulting in a paradoxical contraction of the pelvic floor muscles when the patient attempts to push. The puborectalis muscle and external anal sphincter may tighten instead of relax, or they may fail to relax sufficiently to open the exit pathway. This creates a functional obstruction, essentially forcing the patient to push against a closed door.
This muscular error means the propulsive force generated by the abdominal muscles meets resistance from the anal sphincter complex. The core issue is the disruption of the normal rectoanal reflex. The failure is not a lack of strength, but a learned, incorrect muscular response that prevents the normal opening of the anal canal during straining. This acquired behavioral problem is the primary mechanical cause of evacuation difficulty.
Recognizing the Signs
The muscular dysfunction translates into symptoms collectively known as obstructive defecation. Patients typically experience chronic, excessive, and often unproductive straining during attempted bowel movements. This straining results from the effort to overcome the functional blockage caused by the unrelaxed pelvic floor muscles.
A frequent complaint is the persistent feeling of incomplete evacuation, where the individual feels stool remains in the rectum after a bowel movement. Due to the difficulty in passing stool, feces often become hard and lumpy, further complicating the process. Infrequent bowel movements, defined as fewer than three per week, are also common.
In severe cases, patients may resort to manual assistance, known as digital maneuvers, to facilitate stool passage. This involves placing fingers near the anus or vagina to apply pressure and aid in emptying the rectum. These symptoms are often severe and are refractory, meaning they do not respond well to standard treatments like dietary fiber or laxatives.
Specialized Diagnostic Procedures
Because dyssynergic defecation is a functional disorder, it requires specialized physiological testing to confirm the diagnosis, as a physical exam alone is often insufficient. Anorectal manometry (ARM) is a fundamental diagnostic tool that measures pressure changes in the rectum and anal canal. This test involves inserting a thin catheter with pressure sensors to assess the resting and squeeze pressures of the anal muscles.
Crucially, ARM identifies the dyssynergic pattern by observing the patient during a simulated defecation attempt. Instead of the expected drop in anal pressure, the manometry tracing will show a paradoxical increase or an insufficient relaxation of the external anal sphincter and puborectalis muscle. The test also assesses rectal sensation, which is impaired in a significant number of patients with this condition.
The Balloon Expulsion Test (BET) is a simple, highly specific test often used in conjunction with manometry. A small balloon, typically filled with 50 mL of water, is placed in the rectum, and the patient is instructed to expel it as if passing stool. The inability to expel the balloon within a standard time frame, often set at one minute, strongly suggests a pelvic floor evacuation disorder.
An alternative imaging technique, such as defecography, may also be used, especially when other results are inconclusive or to rule out structural issues. Defecography uses X-rays or magnetic resonance imaging (MRI) to record the dynamic process of defecation after the patient is given a contrast agent. This technique provides a visual assessment of the anorectal angle and the completeness of rectal emptying.
Biofeedback and Other Therapies
The primary and most effective treatment for dyssynergic defecation is biofeedback therapy (BFT), considered the gold standard. This therapy is a form of neuromuscular training designed to correct the learned, incorrect coordination pattern of the pelvic floor muscles. Biofeedback uses specialized sensors, often integrated with manometry equipment, to provide the patient with real-time visual or auditory feedback about muscle activity.
Patients learn to consciously relax the external anal sphincter and puborectalis muscle while simultaneously increasing abdominal pressure, mimicking the correct pattern of defecation. The process involves repeated training sessions under the guidance of a specialized therapist, often resulting in successful symptom improvement in over 60% of patients.
While biofeedback is the targeted intervention, adjunct therapies are important for overall bowel health management. These include education on proper toileting posture and habits, such as responding promptly to the urge to defecate. Dietary adjustments, including adequate fiber intake and fluid consumption, are recommended to achieve a softer, more easily passable stool consistency. Laxatives alone cannot resolve the fundamental problem of muscle incoordination, making specialized retraining necessary.