Slow transit constipation (STC) typically involves the unusually slow passage of faeces through the colon (large intestine). This can lead to chronic constipation and uncontrollable soiling. STC may mimic or coincide with Hirschsprung’s disease.
Diagnosis of slow transit constipation (STC)
The diagnosis of STC first involves confirming slow transit of faeces with “marker studies” in which the patient swallows a capsule containing either radiolabelled or opaque numbered markers that show up on x-rays taken repeatedly over several days or a week.
Ano-rectal causes of constipation due to obstruction need to be excluded. This includes short-segment Hirschsprung’s disease involving the rectum in which the nerves (ganglions) of the enteric nervous system of the colon and rectum (myenteric plexus) are missing. Hirschsprung’s disease can be excluded by taking a full-thickness rectal biopsy. It is also important to exclude other disorders of the rectum including a rectum that collapses on itself (rectal prolapse) or bulges excessively into the vagina (rectocele) or abdomen (enterocele) during straining, as these can all lead to a rectum that is unable to evacuate its contents (obstructive defecation). Weakness of the pelvic floor with excessive downwards movement on straining (pelvic floor descent) can similarly cause constipation due to obstructive defecation. All of these conditions can occur separately, or be combined (tetralogy of fallout). They are associated with classical symptoms, and these combined with a real-time x-ray taken during defecation (defecating proctography), will help suggest whether one of these conditions is responsible.
Medical management of slow transit constipation
Slow transit constipation can often respond to biofeedback and regular laxatives.
Biofeedback is a risk-free approach that has been reported as effective in approximately 60% of patients with slow transit constipation. Uncoordinated (dyssynergic) defecation is common and affects up to half of patients with slow transit constipation. It is due to the inability to coordinate the abdominal and pelvic floor muscles to evacuate stools. Biofeedback therapy teaches coordination of the abdominal and pelvic floor muscles, and positioning to encourage evacuation. It also involves the use of a prospective stool diary to encourage practices that promote regularity.
Several randomised trials have demonstrated that biofeedback is not only efficacious but superior to other modalities such as laxative or sham training.
Stimulant laxatives such a bisocodyl (Bisolax®) are considered first-line therapy, beginning at 10mg twice a day. This can be combined with an osmotic laxative such as lactulose (Lactulax®) beginning with 30ml twice a day. There is no evidence to suggest that chronic use of such laxatives is harmful. Periodic use of bowel preparation solutions such as polyethylene glycol (Glycoprep®) may be needed.
Surgery for slow transit constipation
Surgery for slow transit constipation is a last resort, and indicated only in severe cases that have failed medical management. The surgical options include:
- sacral nerve stimulator (SNS), which is thought to result in chemical alteration (neuromodulation) of the nervous system of the colon (myentetic plexus),
- the insertion of a Chait tube caecostomy, that allows regular irrigation and evacuation of the colon, or
- a Total colectomy which the entire colon is removed, with small bowel joined directly to the rectum.