Slow transit constipation (STC) is a specific form of chronic functional constipation and a motility disorder. This means waste moves through the large intestine at a much slower pace than normal, resulting in infrequent and difficult-to-pass bowel movements. The colon’s reduced ability to propel stool distinguishes STC from other types of constipation.
Underlying Causes and Mechanisms
The large intestine propels waste using coordinated, rhythmic muscular contractions called peristalsis. This activity is governed by a complex network of nerves within the intestinal walls known as the enteric nervous system (ENS). The ENS manages motility independently of the central nervous system.
STC arises when this finely tuned process is disrupted, often due to a neuropathy or a myopathy. A neuropathy refers to problems with the enteric nerves themselves. There may be a reduced number of nerve cells, or these cells may be abnormal in structure or function, leading to poor signaling for the muscles to contract.
A myopathy involves a problem with the colonic muscles, which may lack the strength or coordination to respond effectively to nerve signals. In many cases, there is evidence of both nerve and muscle-related issues. Studies have shown a reduction in specific neurotransmitters and specialized pacemaker cells, called the interstitial cells of Cajal, which generate the rhythmic electrical activity that triggers muscle contractions.
Symptoms and Indicators
The symptoms of STC overlap with general constipation but have distinguishing features. The most prominent symptom is a markedly infrequent need to have a bowel movement, sometimes as few as one or two per week. This is often accompanied by persistent abdominal bloating, a feeling of fullness, and abdominal pain. Nausea and a poor appetite are also commonly reported.
A significant indicator of STC is a lack of response to standard treatments like increased dietary fiber or common over-the-counter laxatives. For those with STC, these approaches are often ineffective. Increasing fiber can even worsen symptoms like bloating and discomfort because the slow-moving colon is unable to manage the added bulk.
The Diagnostic Process
Confirming a diagnosis of STC requires ruling out other causes and measuring the speed at which waste moves through the colon. A healthcare provider will first exclude structural problems or blockages. The primary tool used is a colonic transit study, called a Sitz marker test.
In a Sitz marker study, the patient swallows a capsule containing small, radiopaque markers visible on an X-ray. After several days, an abdominal X-ray is taken, usually on the fifth day. In a person with normal transit, most markers will have passed. If a significant number of markers remain scattered throughout the colon, it indicates a global delay in transit consistent with STC.
Other tests may be used to eliminate different conditions. Anorectal manometry measures the muscle strength and reflex activity in the rectum and anus to help identify pelvic floor dysfunction. Defecography uses imaging to evaluate the rectum during a bowel movement. These tests help confirm the primary issue is slow movement through the colon, not a problem with the final stage of evacuation.
Management and Treatment Strategies
Treatment for STC is approached in a stepwise fashion, starting with conservative medical management. While over-the-counter fiber and some laxatives may not be effective, specific prescribed laxatives can be. Osmotic laxatives, like polyethylene glycol, draw more water into the colon to soften stool, while stimulant laxatives, like bisacodyl or senna, directly trigger the intestinal muscles to contract.
When initial laxatives do not provide sufficient relief, prescription medications that enhance motility, known as prokinetics, may be introduced. These drugs stimulate the propulsive contractions of the colon. Prucalopride is a medication in this class that acts on serotonin receptors in the gut wall to improve colonic movement.
For constipation complicated by pelvic floor dysfunction, biofeedback therapy may be recommended. This technique uses sensors to give patients real-time feedback on their muscle activity, helping them learn to relax and coordinate their pelvic floor muscles for easier bowel movements. It is a specialized therapy aimed at retraining muscle function.
In severe cases where other medical treatments have failed, surgery may be considered. The standard procedure is a subtotal colectomy with ileorectal anastomosis. This involves removing most of the colon and attaching the small intestine directly to the rectum. This is a major operation reserved as a last resort for patients with confirmed slow transit.