Zsa Zsa Weerts

Chapter 1 20 Aims & outline of this thesis IBS is a highly prevalent disorder of brain-gut interaction, of which the complex and multifactorial pathophysiology remains poorly understood. The socioeconomic burden associated with IBS is substantial and is likely caused by a combination of the challenging diagnostic process, the chronic relapse-remitting nature of IBS, and the overall meagre efficacy of the current therapeutic array. Further insight into these contributing factors may help prevent the drainage of precious health care costs and improve patients’ quality of life. We studied the change in diagnostic criteria and how this affects the IBS population, and its impact on quality of life in part I of the current thesis. As adequate treatment of the most cardinal symptom, abdominal pain, is often unsatisfactory, we addressed TRP channels as potential therapeutic targets and investigated the efficacy and cost- effectiveness of peppermint oil in part II of this thesis. In 2016, the Rome diagnostic criteria for IBS were revised to the more stringent Rome IV criteria. Until then, most studies had been based on prior criteria, such as Rome III, and it was unknown which Rome III IBS patients were likely to meet the Rome IV criteria. This however, is important to know because the Rome defined IBS population is the target population for randomized clinical trials to investigate treatment response of novel treatment strategies. It is also meaningful to assess how the change in definition could affect clinical practice because the criteria are pivotal in the clinical diagnostic process and are meant to reduce the number of diagnostic investigations (and thus costs) by making a positive diagnosis. Therefore, in chapter 2 , we investigated demographic, clinical, and psychosocial differences between Rome III and Rome IV IBS subjects, using diary-based surrogate Rome IV criteria in a large and well-defined patient cohort. In most patients with IBS, symptoms fluctuate over time. Given that knowledge of factors affecting the natural disease course can help in the search for new patient tailored treatment strategies, it is pertinent to identify predictors for long-term symptom severity and quality of life. Therefore, we evaluated symptom evolution and characteristics that could predict the disease course over a five-year follow up period in patients participating in the Maastricht IBS cohort in chapter 3. In the search for cost-effective treatments for patients with IBS, TRP channels are promising targets for therapeutic interventions. Growing evidence indicates that TRP