The prevalence of FDD worldwide ranges from 13–81% of FC patients depending on different population and definitions2. Our study retrospectively investigated a consecutive Chinese FC population and 62.73% were FDD. The high prevalence might be related to the severe symptoms and unsatisfied treatment experience of patients in our hospital. In view of the difficulty in telling FDD from other FC subtypes with symptoms alone, anorectal physiological testing and imaging are warranted21.
Function testings need to be carried out in specialist centers, including ARM, BET, CTT test, defecography, EMG, etc22. However, given the limited availability of these investigations in primary clinics, the work-up for FDD often remains inadequate23. Current guidelines from the American Gastrointestinal Association (AGA) recommend ARM with or without BET as a basic test24, followed by EMG, barium or magnetic resonance(MR) defecography if necessary25, 26. ARM and BET are pivotal in identifying patients with FDD27, 28. However, limited agreement between these tests has been achieved and there is no single gold standard for FDD diagnosis7.
We diagnosed FDD using BET, HR-ARM and CTT. The majority of our patients with FDD showed fine agreement in BET and HR-ARM results. Compared with other physiology testings such as barium or MR defecography, currently ARM and BET are more available, less costly and correlated with treatment outcomes6. BET is utilized as a direct tool to indicate defecation dysfunction while HR-ARM as an indirect tool. BET can be used to assess rectoanal coordination and the abnormal result is indicative of an impaired defecatory maneuver and may predict the response to biofeedback therapy29. HR-ARM provides a comprehensive assessment of rectoanal pressures and motor coordination combined with an assessment of rectal sensation and rectoanal reflexes30. The pressure measurements can identify rectoanal dyssynergia as a cause of FDD31. PFD identified by HR-ARM have been widely used to diagnose and classify FDD due to its convenience and availability in clinical practice11.
84.48% patients with FDD in our study were found showing positive BET and PFD, revealing good consistency between BET and PFD. Compared to other patients with FDD, these patients showed high anal residual pressure, low anal relaxation rate, RAPG and MDI. During normal defecation, there is a rise in rectal pressure, which is synchronized with a relaxation of the external anal sphincter and a decrease in anal pressure. The inability to perform this coordinated movement represents the main pathophysiology mechanism in FDD. This may be related to inadequate pushing force, paradoxical anal sphincter contraction, impaired anal sphincter relaxation, or a combination of above32, 33. Anal residual pressure indicates whether there is a failure in anal relaxation during attempted defecation. Besides, the quantitative parameters of pressure changes in the rectum and anus during attempted defecation, such as anal relaxation rate, MDI and RAG, are useful to diagnose FDD11 and MDI serves as a simple and useful quantitative measure of rectoanal coordination during defecation34. According to our findings, FDD patients with positive BET and PFD mainly had problems with impaired anal sphincter relaxation and paradoxical anal sphincter contraction, which may be associated with abnormal external anal sphincter (EAS) and/or puborectalis muscle contraction35.
A previous study suggested impaired defecation in patients with FDD was mainly attributed to increased resistance to evacuation, rather than weak propulsive force and DD would be more predominant than IDP in FDD11. Our study showed the percentage of consistent results was larger in DD patients. Furthermore, high anal sphincter pressure phenotype of FDD was more frequently observed when BET and PFD were both positive. These findings revealed patients with DD usually have both positive BET and PFD. Meanwhile, their impairment of EAS and/or puborectalis muscle contraction is likely more severe.
Zakari et al found that men had higher median resting anal pressures and mean squeeze pressures compared to women36. Different from its results, no difference of resting anal pressure and squeeze pressure between genders was observed in our study. Instead, the percentage of males is larger in Consistent Group and males tended to suffer much more paradoxical anal sphincter contraction and impaired anal sphincter relaxation. A previous study found that males with FC were significantly more likely to suffer defecation dysfunction than female patients37. In addition, our results showed increasing age played a negative role in anal relaxation dysfunction during defecation and patients with positive BET and PFD were older than other patients with FDD. The findings above indicated male and age might predict severe defecation dysfunction.
Four of the six symptoms in Rome IV criteria for constipation are highly indicative of FDD: straining, sensation of incomplete evacuation, sensation of anorectal obstruction/blockage, and manual maneuvers to facilitate defecation38. While the BSFS is commonly used in clinical practice, a previous study did not find a report of hard or lumpy stools associated with FDD39. In this study, defecation symptoms assessed by PAC-SYM were more severe in Consistent Group. However, SBMs, BSFS and defecation duration did not differ between two groups. It suggested FDD patients with positive BET and PFD might have more severe clinical manifestation, especially the defecation dysfunction symptoms. Furthermore, constipation is associated with high psychological stress and impaired QOL40 and FDD carries a significant impact on them3, 41. Our findings suggested FDD patients with positive BET and PFD suffered more anxiety and impaired QOL, particularly physical health related QOL. Furthermore, we found that anxiety played a role in defecation symptoms and the impaired QOL might be related to anxiety and defecation symptoms. Depression did not make sense whether BET was consistent with PFD in this study. More relevant evidence concerning the relationship between symptoms, mental health and QOL in FDD patients is warranted.
BET has a diagnostic accuracy sufficient to identify patients without FDD. Patients with negative BET may not need other onerous tests to exclude FDD12. In our study, positive BET alone had a good diagnostic sensitivity and NPV for FDD as well as its two subtypes so it could be used as an excluding tool. Besides, BET was reported to have high specificity as a diagnostic tool for FDD42. According to the 3 minutes criteria of BET based on ARM and EMG during biofeedback training, PPVs were 93% and 100%, respectively43. However, the specificity and PPV of BET in our study were relatively low compared to some previous studies. The difference might be attributed to patients without FDD failing BET with left lateral decubitus position. When positive BET was combined with PFD, the specificity and PPV rose evidently to 100%, indicating that positive BET and PFD can be used as a good screening tool for FDD.
A digital rectal examination (DRE) is helpful to assess the anal sphincter and puborectalis muscle tone during squeezing and attempted defecation44, which could indicate PFD. DRE has been reported with a sensitivity of 75% and specificity of 87% for identifying DD45. Based on our findings, PFD identified by DRE and BET might be sufficient for screening FDD when ARM or defecography is not available in primary clinics.
This study investigated the characteristics of FDD patients with positive BET and PFD. We also explored possible pathophysical mechanism and associated risk factors of patients’ severe symptoms and impaired QOL. Furthermore, we evaluated the diagnostic value of positive BET and PFD and then suggested BET combined with DRE being applied in primary clinics to help identify FDD.
However, there are also some limitations as follows. First, this study was performed with data retrospectively analyzed in a single tertiary care center, which might result in data scarcity and lack of universality. Second, Other diagnostic tests that might be helpful to diagnose FDD, such as defecography or EMG, were only performed in a minority of our patients. Furthermore, position is a key component as demonstrated in a study recruiting 25 healthy people that found an increase in dyssynergia in the left lateral position (36%) compared with the seated position (20%)46. Left lateral position was adopted in BET in our study, which might cause false positive result and low specificity of BET. However, concordance between BET performed in the left lateral position or seated position was observe in a previous study47.
Complex procedures are needed to diagnose FDD and it is hard for primary care or secondary gastroenterology practices outside referral centers42 to tell FDD from other constipation subtypes. We found that positive BET and PFD could be an ideal screening tool to identify FDD, in which PFD could be diagnosed by ARM or DRE instead. FDD patients with positive BET and PFD suffer severe defecation symptoms, anxiety and impaired QOL. Paradoxical anal sphincter contraction or impaired anal sphincter relaxation might be the key factor.
In conclusion, patients with FDD request more concern and need to be treated properly based on clinical manifestations and specific pathophysiology. Positive BET and PFD shed light on diagnosing FDD more conveniently.