Zsa Zsa Weerts

Summary 253 A Summary Irritable bowel syndrome (IBS) is disorder of gut-brain interaction, previously known as a functional gastrointestinal disorder and is characterized by chronic recurrent abdominal pain and altered bowel habits. It is highly prevalent affecting 5-15% of the population depending on the criteria used and is associated with a pronounced impact on quality of life. The underlying pathophysiology of IBS is multifactorial, complex and incompletely understood and as a consequence, reliable biomarkers to diagnose IBS are currently lacking. This makes IBS a diagnosis which is, according to current consensus, merely based on symptoms. Symptoms vary widely both within and between patients, reflecting the complex and heterogeneous phenotype of IBS. Despite its prevalence and substantial negative impact on patients, treatment options are currently limited and are moderately effective at best. The relative lack of effective therapies adds further to the large associated socioeconomic burden. This thesis covers several aspects concerning IBS, from the diagnostic Rome criteria and symptom evolution over time ( part I ), to the investigation of therapeutic targets, with a special focus on treatment with peppermint oil, its potential mechanisms of action and its cost-effectiveness ( part II ). Part I - Epidemiological aspects and clinical manifestations of Irritable Bowel Syndrome Currently, diagnosis of IBS is made based on the presence of typical clinical symptoms which are incorporated in the Rome criteria and include abdominal pain and aberrant defecation such as constipation, diarrhea or a combination of the two. The Rome criteria have been modified every few years, which has led to some variation in IBS patient populations over time, depending on which criteria were used to diagnose IBS. The most recent version of the criteria is the Rome IV, published in 2016, which was expected to be more stringent than the prior Rome III due to the requirement of abdominal pain at least once a week instead of three days per month. In addition, the presence of pain instead of discomfort alone is a necessity. In chapter 2 , we compared the prevalence of IBS according to the Rome III and IV criteria in the well characterized Maastricht IBS Cohort. Of 404 patients that were diagnosed with IBS using the Rome III criteria, between 87% and 62% was likely to also fulfill the Rome IV criteria. When comparing clinical characteristics between Rome III IBS patients and those also fulfilling the Rome IV criteria, we found that the Rome IV IBS population reflected a subgroup of Rome III IBS patients that was more often female, with more severe GI