Zsa Zsa Weerts

Summary 257 A Summarizing, we demonstrated a moderately positive effect of peppermint oil on IBS symptoms ( chapter 7 ). Peppermint oil is inexpensive, widely available and has few adverse events. Taken together with the modest gains in quality of life adjusted years and the results of chapter 8 where we show that peppermint is likely cost-effective, we conclude that peppermint oil seems an appropriate first-line treatment for patients with IBS. More research and long-term data are necessary to confirm the effectiveness and cost-effectiveness of peppermint oil. Since there are no reliable biomarkers in IBS, end-of-day symptom diaries are considered the gold standard to assess treatment response. For the PERSUADE study, we used a custom-made digital framework for data-collection consisting of a daily digital symptom diary (custom smartphone application), web-based patient questionnaires (regarding e.g. demographics and life style, IBS symptom severity, and anxiety and depression), and an electronic case report file (eCRF) for investigators to report in. This digital framework and the results of the study investigating the feasibility of this digital data collection method is described in chapter 9 . We showed that the mean overall compliance rate to the symptom diary was 88%. Patients’ compliance to the additional web-based questionnaires and investigators’ compliance to the eCRF were also very high, i.e. both more than 99%. Missingness due to technical issues was limited to one question. The data collection framework thereby was shown to lead to a standardized state-of-the art data collection with excellent completeness and can be used for future RCTs. Due to a slight decrease in patient compliance to the digital diary throughout the study, this method might be less suitable for trials of longer duration. Finally, in chapter 10 , we provide an overview of the major findings presented in this thesis, integrated the different topics that were discussed in the different chapters, tried to place results in the broader scope of IBS research and discussed new insights and future perspectives. Although this thesis provides new insights in different aspects of IBS research and treatment, its high prevalence, associated substantial socioeconomic burden, and impact on quality of life on patients affected will continue to necessitate extensive future research into the field of disorders of gut-brain interaction and particularly IBS.