Diagnostic Value of the Anal Endoluminal Functional Luminal Imaging Probe for the Diagnosis of Anismus: An Exploratory Study

Background and Aims The aim of this exploratory study was to evaluate the performance of the anal EndoFLIP in diagnosing anismus in patients with functional constipation and suspected to have a dyssynergic defecation based on a composite reference standard (anorectal manometry, surface electromyography, and defecography). Methods Patients underwent anorectal manometry, surface electromyography, and defecography. At least two of the three tests needed to be positive to diagnose anismus. Anal EndoFLIP was performed during push maneuvers at 40 and 50 mL of distension, and pressure‐cross‐sectional‐area (CSA) loops were built for each push maneuver to identify parameters that could best predict a diagnosis of anismus (ROC curve analysis). Two‐variable CSA–pressure classifiers were evaluated using nested repeated five‐fold cross‐validation. Results Diagnosis of anismus using the composite reference standard was made in 29/57 patients (50.8%). An analysis of CSA‐pressure loops indicated that, at 40 mL of distension, maximal absolute ΔCSA and maximal relative ΔCSA were lower compared to patients without anismus ( p < 0.001). Among quantitative CSA indices, an exploratory threshold under 12.8 mm 2 for a maximal absolute ΔCSA at 40 mL provided the highest accuracy and AUC (0.81) and excellent specificity (0.93) for the diagnosis of anismus. Using nested repeated cross‐validation, two‐variable GLM and CART classifiers yielded mean out‐of‐sample AUCs of 0.767 and 0.764 at 40 mL and 0.754 and 0.658 at 50 mL, respectively. Conclusion The results suggest that anal EndoFLIP may help distinguish patients with anismus from those without. Further external validation studies are needed to establish clinically applicable thresholds. Trial Registration Clinical.trials.gov : NCT04155307