Diagnosing constipation

Anorectal manometry. Manometry allows the function of the anal sphincter to be assessed at rest and during defecation, as well as the reflexive activation of the pelvic floor. This can measure rectal sensitivity and compliance, and relaxation of the external and internal anal sphincter. It is indicated in patients who do not respond to first-level hygiene and dietary measures or laxatives. It is useful in the diagnosis of functional defecation disorders and for the correct selection of patients who are candidates for rehabilitation treatment using anorectal biofeedback.

Balloon expulsion test. This consists of introducing a balloon in the rectum. It is filled with 50 ml of water that the patient must evacuate. Although the methodology for this test varies, the most common approach is to determine the time it takes for the patient to expel the balloon into the toilet. This test is indicated for patients who do not respond to treatment with lifestyle changes and first-line laxatives, and when constipation is suspected to be caused by a bowel movement disorder.

Determining colonic transit time (CTT). This is a very useful examination for patients suspected of having slow colonic transit as the cause of constipation. It is determined by ingesting small radiopaque markers made of a light plastic substance and then performing serial abdominal X-rays to quantify colonic transit time. The most commonly used protocol in Spain is to take X-rays at 4 and 7 days, and sometimes even on the 10th day. Excessive delay in the progression of these markers and their retention in the colon are indicative of a diagnosis of colonic inertia or colonic hypomotility. This test is indicated in patients who do not respond to treatment with lifestyle changes or first-line laxatives and when constipation is suspected to be caused by colonic hypomotility.

Video defecography. Defecography allows assessment of the anatomy and functional changes of the anorectum and is useful when anatomical causes of constipation, such as enterocele or intussusception are suspected, and in patients with pelvic floor dysfunction. It is considered an adjunctive test and, therefore, is not recommended as a sole examination for the diagnosis of these conditions. In this test, 150 ml of barium is inserted into the patient’s rectum. They are asked to perform Valsalva manoeuvres (coughing, pushing) and the elimination is monitored. There are two techniques for identifying anatomical abnormalities: 

• Fluoroscopy. This has the advantage of being accessible and quick, but it is irradiating. 
• MRI. This has the advantage of observing all the pelvic floor organs during defecation without irradiation, but it is expensive and less accessible than the first. Currently, the Clínic offers magnetic resonance defecography.