Among patients with constipation, reduced rectoanal gradient found during high-resolution anorectal manometry (HR-ARM) is the strongest parameter for predicting how a patient is likely to perform on a rectal balloon expulsion test (BET). Findings of both reduced rectoanal gradient and abnormal BET should be considered diagnostic for a defecatory disorder.
Those are the findings of a study out of the Mayo Clinic in Rochester, Minn., which wasin Gastroenterology. The research could help streamline diagnosis of defecatory disorders: Currently there is a lack of consensus on what tests should be performed and in what order to achieve a reliable diagnosis, according to the authors.
The authors recommend that, in patients with a suggestive history, a prolonged time on BET or reduced rectoanal gradient individually indicate a probable defecatory disorder, while the presence of both could be considered diagnostic even in the absence of defecography.
The research should provide clarity about the findings from HR-ARM, which can be complex, according to Kyle Staller, MD, who was asked to comment on the study. “You get lots of different numbers, you get lots of different parameters [with HR-ARM], and figuring out which ones are really relevant is somewhat difficult. [This study] is really a tour de force that distills down many of these parameters into some that we might want to pay attention to more than others,” said Dr. Staller, who is director of the GI Motility Laboratory at Massachusetts General Hospital and a professor of medicine at Harvard Medical School, both in Boston.
He pointed out that one limitation of the study is it didn’t attempt to answer the question of what parameters predict benefit from biofeedback therapy.
“I think the practice right now is that we tend to put the most weight on the balloon expulsion test. I think what this paper convincingly argues is that maybe someone who has an abnormal rectoanal gradient and a normal balloon expulsion test should also be referred for biofeedback with the caveat that we still don’t know if they’re going to do well on biofeedback or not,” said Dr. Staller.
The study included 658 patients, 474 with constipation and 184 healthy controls. In addition to HR-ARM and BET, 158 underwent defecography. Females made up 89% of constipated patients and 73% of healthy individuals. Healthy individuals were younger than constipated individuals (median age 35 versus 49 years).
Overall, 11% of healthy patients and 32% of constipated patients had prolonged BET time (P < .001) and 11% and 21% had a reduced rectoanal gradient on HR-ARM (P = .003). Among those with a normal BET time, 13% had a reduced rectoanal gradient, compared with 34% of those with a prolonged BET time (P < .001).
The authors report that HR-ARM variables had good specificity but worse sensitivity for predicting prolonged BET. The rectoanal gradient was the best-performing variable, with a specificity of 85% and a sensitivity of 36%.
HR-ARM and BET findings were associated with reduced rectal evacuation found on defecography. The median rectal evacuation was 79% if both BET and rectoanal gradient were normal, 35% if either one was abnormal, and 3% if both were abnormal (P < .001). Having either prolonged BET time or reduced anorectal gradient alone had a 73% sensitivity and specificity of 72% for incomplete evacuation on defecography. If both abnormalities were present, the sensitivity was 31% but the specificity was 95%.
A reduced rectoanal gradient was associated with incomplete rectal evacuation (odds ratio, 4.35; P = .002); prolonged BET time showed a similar association (OR, 4.57; P < .001).
The authors proposed terminology to help differentiate the findings: “probable defecatory disorder,” or “probable DD,” to describe patients with one abnormal result from the three tests and “definite DD” for those with two abnormal test results. “Although a single abnormal finding may be a false-positive result, pursuing a trial of biofeedback therapy for patients with a probable DD may be reasonable, especially when defecography is not feasible. However, this approach should be confirmed by prospective studies that assess the response to anorectal biofeedback therapy in patients with probable and definite DD, as defined above.”
The authors disclosed no conflicts of interest. Dr. Staller has consulted for GI Supply.