In adults with functional constipation, dyssynergic defecation (DD) is common and affects up to 50% of patients referred with chronic constipation in tertiary care center.¹ In patients with DD, the gold standard for management is pelvic floor retraining with relaxation and biofeedback therapy (BFT).² Several randomized controlled trials showed that biofeedback therapy is effective for improvement of symptoms and anorectal parameters in 70-80% of patients with DD and more effective than other modalities including laxatives, diet and education.^3-5 However, some patients with DD do not respond to BFT. Furthermore, BFT is not widely available and labor-intensive, which means that the success of BFT mainly depends on the quality of the therapist-patient relationship and the skills and experience of the therapist. Therefore, previous studies tried to find the factors associated with response to BFT to choose patients with DD who are likely to have good response for BFT. Favorable predictors included older age, harder stool, high intrarectal pressure during straining and low defecation index. However, there were inconsistencies in results, especially conventional manometry parameters due to small sample sizes, different BFT protocols, and different treatment outcomes.^3,6,7

In this issue of the Journal of Neurogastroenterology and Motility, Seo et al⁸ explored anorectal physiology to predict BFT response and suggested a predictive model for BFT response using high-resolution anorectal manometry (HRAM) with spatiotemporal plotting. HRAM has been considered useful for the diagnosis of patients with DD, based on the finding of inadequate anal relaxation or intrarectal pressure. Compared to conventional manometry, it provides color-contoured topographic plots based on the distance, time and amplitude. In Myung’s study with female patients with DD, there were no significant differences in the conventional manometric parameters including anal resting pressure, anal squeezing pressure, defecation index and rectoanal gradient during resting state or simulated evacuation. They suggested integrated pressurized volume (IPV) and IPV ratios of each anorectal segment as new parameters for prediction of response to BFT, which may enable understanding the 3-dimensional structural and temporal relationship and physiology of anorectum during evacuation. IPV can be calculated by multiplying the distance, time and amplitude, which seems similar to the concept of distal contractile integral and integrated relaxation pressure of high-resolution esophageal manometry. The values of IPVs of upper portion of anorectum were lower in good responders for BFT and the IPVs of the upper 1-cm portion showed the best performance for predicting response of BFT with 0.74 of AUC (95% CI, 0.63-0.80). The authors also suggested the partial least squares regression (PLSR) model using 8 IPV parameters, which showed diagnostic value such as 0.84 of AUC (95% CI, 0.76-0.95), 85.5% of sensitivity and 62.1% of specificity. Measured and calculated IPV parameters may be helpful for detecting functional abnormalities of the anorectum during evacuation and predicting responsiveness to BFT in female patients with DD. Andrianjafy et al⁹ also tried to suggest the factors for response to BFT using 3-dimensional HRAM, in that patients with rectal pressure less than 40 mmHg showed good response to BFT. Considering that the value of IPV represents the rectal pressure, Seo et al⁸’s study showed consistent findings. This study has several limitations. It was a retrospective single and tertiary center study which included only female patients with DD. Second, the treatment outcome measurement was based on only symptom questionnaire, not including physiologic parameters such as balloon expulsion time, HRAM parameter or defecographic findings and the therapist-patient relationship and therapist’s skill and experience. I hope future studies of IPV parameters and PLSR model as the role as the predictive factors in a large sample of prospective patients including male patients and variable aged groups.

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