513 PHENOTYPIC CHARACTERIZATION OF FUNCTIONAL DEFECATORY DISORDERS USING SIMULTANEOUS MR DEFECOGRAPHY AND MANOMETRY

Abstract

BACKGROUND & AIMS High resolution manometry (HRM) is widely used to diagnose defecatory disorders (DD). Contrary to conventional concepts, many healthy people have a negative rectoanal gradient during evacuation (ie, anal > rectal pressure), which undermines our understanding of the mechanisms of normal defecation and DD. Perhaps this is partly because manometry is performed in an empty rectum in the left lateral position. Aimed to better understand the mechanisms of normal defecation and DD, we simultaneously measured rectoanal pressures and evacuation in healthy and constipated women. METHODS We assessed anorectal and abdominal wall motion and rectal evacuation of gel with MR defecography, and pressures with water-perfused manometry in 28 healthy women and 26 women with constipation. Phenotypes were identified by K-means cluster analysis. The unconditional exact test (chi-squared statistic) evaluated the relationship between these clusters and outcomes, ie, balloon expulsion time [BET], subject status (healthy versus constipation) and evacuation. RESULTS Twenty seven participants (19/27 healthy women, 8/26 patients, P 25% of gel). The BET was >60s in 4 controls and 9 patients (P=0.1). The cluster analysis identified 3 distinct clusters, which were defined by pressure and motion variables (Figure 1); BET and rectal evacuation were not variables in the cluster analysis. During evacuation, the rectal pressure, anorectal junction descent, abdominal diameter, and anal diameter were all smaller while the anal canal was longer in cluster 1 (3 evacuators [E], 21 nonevacuators [NE]) (P CONCLUSIONS Manodefecography uncovers 3 clusters in DD. Cluster 1, which predominantly comprises nonevacuators, is characterized by limited abdominal expansion, a spastic pelvic floor, and inadequate rectal pressure during evacuation. By contrast to cluster 1, 24 of 30 (80%) subjects in clusters 2 and 3 were evacuators. In these subjects, abdominal expansion, rectal pressure, and anal opening were preserved; resting anal pressure was lower in cluster 2 than 3. Most patients with DD do not have isolated rectal or anal dysfunctions but rather a combination of impaired abdominal expansion, rectal propulsion, anal opening, and perineal descent during evacuation. Download : Download high-res image (170KB) Download : Download full-size image Figure 1 . The cluster analysis, which was based of 7 variables (Table 1), uncovered 3 distinct clusters. These clusters are plotted using the first two principal components from the 7 variables. The principal component analysis is only used to depict the data; it was not used for the K-means cluster analysis. Cluster 1 predominantly comprises nonevacuators (filled symbols), while clusters 2 and 3 are predominantly evacuators (open symbols). These clusters (1 versus 2 and 3) were associated with evacuator status (P Download : Download high-res image (69KB) Download : Download full-size image Table 1 . Table showing the values of the variables corresponding to centroids of the clusters. During evacuation(e), cluster 1 (3 evacuators[E], 21 nonevacuators [NE]) had lower rectal pressure, anorectal junction descent, abdominal diameter, anal diameter, and a longer anal canal. Cluster 2 (15 E, 4 NE) was characterized by lower anal resting pressure. Compared to clusters 1 and 2, patients in cluster 3 (9 E, 2 NE) had greater anal resting pressure but more anal relaxation during evacuation.