Els van de Vijver

94 Methodological limitations of the review The cross-sectional design of most included studies precludes the ability to draw conclusions concerning the causal relations between variables. Prospective observational cohort studies are needed to gain more insight into the direction and mechanism of the identified associations. If prospective cohort studies are conducted in ethnically and socioeconomically diverse groups of children and adolescents, causative factors of fatigue can be identified, and these could potentially lead to more efficacious ways of treating fatigue in adolescents with IBD. Implications for clinical practice Future research opportunities The mechanism underlying fatigue in children and adolescents with IBD remains poorly understood. Fatigue is a subjective sensation and presents with a multitude of symptoms, which makes it difficult to describe, measure and quantify. Past studies have mainly focused on one aspect of fatigue. Future studies should explore fatigue manifestations at several levels simultaneously, including illness-related aspects (such as ongoing inflammation, disease activity, medication use and pain), physical functioning (health- related quality of life, sleep quality and disability), and psychobehavioral factors. Chapter 5 94