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335 Summary and discussion SUMMARY AND DISCUSSION In this thesis, we discussed novel insights into the epidemiology, evaluation and management of functional defecation disorders (FDDs). Childhood FDDs comprise two distinct clinical entities; functional constipation (FC) and functional nonretentive fecal incontinence (FNRFI). 1 FC is characterized by hard, infrequent stools, often accompanied by fecal incontinence as a result of withholding behavior. 2 In children with FC, hard, large diameter stools frequently result in painful defecation, which prompts withholding behavior resulting in a vicious circle that can prove hard to break. 2 FNRFI on the other hand is characterized by fecal incontinence of a different nature, fecal retention plays no role here. 3 In children with FNRFI, urinary incontinence and psychological comorbidity are not uncommon. 3 Part I of this thesis describes epidemiological studies on FDDs and associated problems. In chapter 1 we describe a systematic review on the worldwide prevalence of FDDs in children. We included 37 studies, of which 35 reported on the prevalence of FC and 15 reported on the prevalence of FNRFI. All included studies used the Rome III criteria to define FDDs. The prevalence of FC ranged from 0.5% - 32.2%, with a pooled prevalence of 9.5% (95% CI 7.5-12.1). For FNRFI, the prevalence ranged from 0.0%-1.8%, with a pooled prevalence of 0.4% (95% CI 0.2-0.7). Interestingly, we found that the reported prevalence of FC was higher in Europe and the Americas compared to Asia. We hypothesized that this could be due to cultural or dietary differences between these continents. This was the first systematic review on this topic to solely include studies using the Rome III criteria which allowed for a meta-analysis. Moreover, it was the first systematic review to evaluate the prevalence of FNRFI in general. Prior to our systematic review, the most recently published and frequently cited systematic review on the prevalence of FC had included studies which had applied various criteria for the diagnosis of FC, ranging from self-report to the Rome II and III criteria. 4 The authors included 17 pediatric prevalence studies and reported that the prevalence of childhood FC ranged between 0.7% and 29.6%, with a median of 12%. 4 No meta-analysis of the data was performed, most likely because of heterogeneity of the included studies. Over the past decade, the number of published prevalence studies regarding functional gastrointestinal disorders (FGIDs) has increased substantially. 5,6 Furthermore, standardized, validated questionnaires such as the Questionnaire on Pediatric Gastrointestinal Symptoms–Rome III Version (QPGS-RIII) are increasingly used in these reports. 5,6 This makes it easier to compare studies and provides more robust data. With the publication of the Rome IV criteria, it is desirable and to be expected that future prevalence studies will adhere to these new criteria. 1,7 For FDDs, the changes in the Rome criteria have been minor and it is therefore unlikely that prevalence results will drastically change if the Rome IV criteria are used. 8 However, future studies are needed to confirm this hypothesis.