Certain imaging tests can be performed to determine the cause of constipation. But despite use of sophisticated modern tests many patients with chronic constipation, the cause can not be identified. The imaging techniques which are used in identifying the cause of chronic constipation are defecography (it is a dynamic barium enema including lateral views obtained during barium expulsion), proctography during defecation, scintigraphy, electromyography, magnetic resonance imaging (MRI) etc.
Defecography can abnormalities in many patients. The important findings that can be shown by defecography are the measured changes in rectoanal angle, anatomic defects of the rectum (like internal mucosal prolapse, and enteroceles or rectoceles) etc. But patients who can be treated by surgery are very few. The surgical patients include severe, whole-thickness intussusception with complete outlet obstruction and an extremely large rectocele which fills preferentially during attempts at defecation instead of expulsion of the barium. The most common cause of outlet obstruction is failure of the puborectalis muscle to relax and this can not be identified by defecography (it requires a dynamic study such as proctography for identification).
Proctography during defecation of stool can help in measuring perineal descent and the rectoanal angle during rest, squeezing, and straining. Confirmation of pelvic floor dysfunction can be done by lack of straightening of the rectoanal angle by at least 15° during defecation.
Neurologic tests like electromyography is generally used to identify the incontinence rather than of those with symptoms of constipation (obstructed defecation).
Scintigraphy is done by checking the expulsion of artificial stool which helps to measure perineal descent and the rectoanal angle during rest, squeezing, and straining. Scintigraphic expulsion quantitates the amount of artificial stool emptied during test and can find out the degree of constipation.
MRI is being used and developed as an alternative to provide more information about the structure and function of the pelvic floor, distal colorectum, and anal sphincters. This is used frequently these days to investigate patients with severe and chronic constipation.
The cause of severe constipation may be due to pelvic floor dysfunction. The pelvic floor dysfunction is suggested by the inability to evacuate the rectum completely, a feeling of persistent rectal fullness, rectal pain, the need to extract stool from the rectum digitally, application of pressure on the posterior wall of the vagina, support of the perineum during straining, and excessive straining at stool. The above symptoms should be differentiated from IBS (irritable bowel syndrome) where the sense of incomplete rectal evacuation is a common symptom.
Some simple tests to determine normal bowel evacuation:
A simple clinical test in the doctor’s clinic can determine a nonrelaxing puborectalis muscle, which is by asking the patient strain to expel the index finger (of the doctor or examiner) during a digital rectal examination. Motion of the puborectalis posteriorly during straining indicates proper coordination of the pelvic floor muscles. Another test to determine if the evacuation of bowel is normal or not is done by placing a balloon-tipped urinary catheter inside rectum and inflated with 50 ml of water. Normally, a patient can expel it while seated on a toilet or in the lateral position; the weight needed to facilitate expulsion of the balloon is generally less than 200 ml (gram) of water, if the evacuation is normal.
Anorectal manometry if used in the evaluation of patients with severe constipation may find an excessively high resting (more than 80 mmHg) or squeeze anal sphincter tone, which suggests anal sphincter spasm, known as anismus. This manometry test can also identify a rare syndrome like adult Hirschsprung’s disease, by the absence of the recto-anal inhibitory reflex.
A formal psychiatric evaluation can be helpful sometimes. Simple psychiatric/psychological evaluation may identify certain psychological causes of constipation like eating disorders, control issues, depression, or post-trauma stress etc. These disorders may respond to cognitive or other intervention and may be important in restoring quality of life to patients who might present with chronic and severe constipation.
Balloon expulsion test is an important screening test for anorectal dysfunction. If the balloon expulsion test is positive, an anatomic evaluation of the rectum or anal sphincters and an assessment of pelvic floor relaxation are than used as tools for evaluating patients, especially in whom obstructed defecation is suspected.
Constipation is persistent, difficult, infrequent, or seemingly incomplete defecation. It is very difficult to define constipation precisely due to the wide range of normal bowel habits. For treatment of constipation, the cause of constipation should be identified. Treatment of constipation is based on the cause of it.
Patients with slow-transit constipation are treated with laxatives. The examples of laxatives are bulk, osmotic, prokinetic, secretory, and stimulant laxatives including fiber, psyllium, milk of magnesia, lactulose, polyethylene glycol (colonic lavage solution), lubiprostone, and bisacodyl. There is also newer treatment modality aiming at enhancing motility and secretion and may have application in special circumstances such as constipation-predominant IBS (irritable bowel syndrome) in females or in severe constipation.
If a 3 to 6 months trial of medical therapy fails with above treatment regimes and patients continues to have documented slow-transit constipation which is not associated with obstructed defecation, the patients should be considered for laparoscopic colectomy (resection or part of colon) with ileorectostomy (joining of ileum and rectum surgically). But these operations should not be done if there is continued evidence of an evacuation disorder or a generalized GI dysmotility. Referral to a specialized center for further tests of colonic motor function should be done in these cases.
The presence of megacolon and megarectum is indication for surgical intervention in constipation. But there may be unacceptable complications after surgery like small-bowel obstruction and fecal soiling, particularly at night during the first postoperative year. Frequency of defecation is 3–8 per day during the first year and 1–3 per day from the second postoperative year onwards.
Patients with severe slow-transit constipation require aggressive medical or surgical treatment. However, approximately only 60% of patients with severe constipation are found to have such a physiologic disorder (colonic transit delay and evacuation disorder). Patients with spinal cord injuries or other neurological disorders require a bowel regime that includes rectal stimulation, enema therapy, and carefully timed laxative therapy.
Patients with evacuation and transit/motility disorder should pursue pelvic floor retraining (biofeedback and muscle relaxation), psychological counseling, and dietary modification first, and than colectomy and ileorectosomy (if colonic transit studies do not normalize and symptoms are intractable despite biofeedback and optimum medical therapy). If patient only has pelvic floor dysfunction, biofeedback training has a 70–80% success rate which is measured by regaining of comfortable stool habits.