Seated anorectal manometry during simulated evacuation: A physiologic exercise or a new clinically useful diagnostic test?

Symptoms such as a feeling of incomplete evacuation, straining, absence of the call to stool, anal blockage, or digitation suggest the presence a functional defecation disorder. As symptoms do not distinguish between patients with and without functional defecation disorder, Rome IV criteria recommend that this disorder is diagnosed when two of three tests are positive: balloon expulsion test (BET), anorectal manometry (ARM), and defecography. However, previous studies have demonstrated that the agreement among these tests is limited. In this issue of Neurogastroenterology and Motility, Sharma et al tested the hypothesis that conducting the ARM in a seated position would increase the diagnostic accuracy of the test in discriminating between patients with normal and prolonged BET. This minireview discusses the current knowledge on the role of the techniques to diagnose defecation disorder and the potential role of the ARM in a seated position.


| BACKG ROU N D
Chronic constipation is a heterogeneous condition characterized by unsatisfactory defecation related to either infrequent or difficult passing of stools, or both. Chronic constipation is one of the most common functional bowel disorders with an estimated global prevalence of 14%, 1 resulting in a significant cost for healthcare systems worldwide 2 and a substantial negative impact on work productivity, which increases with constipation severity. 3 Chronic constipation can present as functional constipation or irritable bowel syndrome with constipation (IBS-C), where the presence of abdominal pain related to change in the frequency and/or consistency of bowel movements differentiates IBS-C from functional constipation, but with a recognized large overlap between the two groups. 4 In both conditions, symptoms such as a feeling of incomplete evacuation, straining, absence of the call to stool, anal blockage or digitation suggest a defecation disorder. The term "functional defecation disorder" is used by Rome IV criteria to identify those patients where "paradoxical contraction or inadequate relaxation of the pelvic floor muscles during attempted defecation and/or inadequate propulsive forces during attempted defecation" could explain the symptoms. 5 Normal defecation requires a very complex interaction between visceral, sensory, and behavioral components: The rectosigmoid should be loaded with normal stools, the resulting rectal distension perceived, and the voluntary act of defecation performed at the right time and in the right way. Last, but not least, the subject should be satisfied with the result.
A number of alterations in the preparatory phase of defecation, the call to stool, and the dynamic of fecal expulsion have been reported in patients with defecatory disorders. [5][6][7] These dysfunctions may co-exist and, when they do, it is unclear whether they are primary or secondary to constipation. Alterations in the behavioral component are often unspecific (ie, they can also be found in normally defecating healthy subjects), and their appraisal may vary depending on the subject's degree of participation in their assessment. 8 Structural alterations such as a rectocele, rectal prolapse, or rectal intussusception may also be present, but their causal role in the symptoms experienced is debated. 9 A patient's dissatisfaction with their bowel habits may well be a result of a combination of objective and subjective components, both an evident dysfunction in the defecation process along with a patient's perception of what normal defecation should be. 10

| CURRENT CRITERIA TO D IAG NOS E FUN C TIONAL DEFEC ATION DISORDER S
Given the multiplicity of factors underlying a normal defecation, it is not unexpected that "there is no single gold standard diagnostic test to diagnose functional defecation disorder and that the agreement among various tests is limited". 11 According to this statement, Rome classification indicates that a functional defecation disorder can be diagnosed (after organic alterations are ruled out) by two of three tests: balloon expulsion test (BET), anorectal manometry (ARM), and defecography. 5 Balloon expulsion test measures the time needed to expel a balloon placed in the rectum. Volumes of water or air in the balloon ranging from as little as 25 ml up to the volume required to produce the desire to defecate have been used, with little standardization in the size, shape, or type of balloon used. 12 The upper limit of the normal time to expel the balloon varies across studies and has been reported as anywhere between 1 and 5 min. 12 A BET that applies 50 ml of water has been found to be predictive of a positive response to biofeedback. 13 Anorectal manometry evaluates abnormal anorectal evacuation patterns such as paradoxical contraction or inadequate relaxation of the pelvic floor muscles and/or inadequate propulsive forces during attempted defecation. ARM also provides a measure of other parameters, such as anal sphincter pressure when resting or squeezing, the presence of anal sphincter relaxation in response to rectal distension, and rectal sensitivity. 14 ARM is normally performed in a left lateral position, which is not the position in which the subject would normally defecate. Previous studies have shown that body position affects the measurement of rectal and anal pressures. [15][16][17] Also in this case, the technique has been used without standardization in protocol and catheters across different centers. However, more recently a first attempt to obtain a standardization of this technique has been done by the London Classification. 18 Defecography assesses both the anatomical and functional abnormalities of the anorectum. 11,19 This radiologic technique dynamically evaluates the anorectum during the simulated defecation of a viscous contrast material, with a consistency similar to stool, while the patient is sitting on a commode. As well as the rectum, opacification can be extended to the vagina, bladder, and/or small bowel.
The technique is applied with considerable variation in terms of patient position, bowel preparation, consistency of contrast materials, types of radiolucent commode, and definitions of normality and abnormality. 19 More recently, defecography has also been conducted by means of MRI, which has the advantage over barium of simultaneously assessing the three pelvic compartments without ionizing radiation, and enabling the quantitative analysis of the acquired images. 20,21 MRI defecography is usually performed with the patient supine.
The idea that two abnormal tests are better than one in the diagnosis of a functional defecation disorder has several limitations.
As reported above, the criteria used to define when the tests are abnormal are quite heterogeneous and poorly standardized for each technique. In the absence of a gold standard for diagnosis, and in the presence of a multifactorial disorder, it can be hypothesized that the precise definition of a combination of different abnormal tests, exploring different pathophysiological mechanisms, might contribute to the definition of more meaningful clinical subgroups. On the other hand, most of the studies in the field have tried to validate the tests by measuring the agreement between the results of two tests that explored the same pathophysiological mechanism, instead of assessing the diagnostic performance of one test, or a sequence of two or more tests, in the patients as compared to healthy subjects.

| CLINI C AL UTILIT Y OF A D IAG NOS TI C TE S T ACCORD ING TO E VIDEN CE-BA S ED MED I CINE: THE LE SSON OF E SOPHAG E AL MANOME TRY
A diagnostic test should be used in clinical practice when, in the presence of suggestive symptoms, it permits the identification of a disease, to which a specific treatment should be applied. 23 The test | 3 of 4

BASILISCO And CORSETTI
is useful for the patient if tested patients have a better quality of life than untested ones, at the end of the diagnostic-therapeutic process.
A practical example of a useful test is the application of esophageal manometry in the diagnosis of achalasia. 24 The test is recommended for patients with retrosternal dysphagia. When a diagnosis is made, patients are effectively treated by esophageal dilation, peroral endoscopic myotomy, or surgery. With these treatments, dysphagia improves and the resulting quality of life in treated patients is better than in those that are left untreated. Why is esophageal manometry so important? Because dysphagia is not specific to achalasia, and the adverse effects of the treatments would be unacceptable if the diagnosis was not correct. Luckily for both patients and doctors, the diagnostic performance of esophageal manometry is ideal because the abnormal motor patterns that define achalasia are not encountered in healthy subjects. 24 Is this the case for ARM, BET, and defecography? In the landmark study by Grossi et al, 25

| WHAT DO WE NEED FOR THE FUTURE?
The assumption that pathophysiological biomarkers might be useful to better characterize patients with defecatory disorders and ultimately allow the targeted treatment of their symptoms is certainly shareable and desirable, but this advantage should be demonstrated

CO N FLI C T O F I NTE R E S T
No competing interests declared.