Els van de Vijver

17 a common, independent and nonspecific symptom that has been identified in numerous chronic health conditions in childhood, including IBD.(21) Fatigue can be a major source of disablement in patients with a chronic disease, and it is often reported as being amongst the most severe and distressing symptoms.(22) Fatigue affects physical, emotional, cognitive and social functioning, and it has an impact on the quality of life. Despite its importance, researchers have rarely included and quantified fatigue in assessments of symptom severity or outcomes of chronic diseases in which it is observed, including chronic obstructive pulmonary disease, cystic fibrosis, chronic renal disease, cancer and heart failure.(22) The quantification of fatigue poses several challenges, due to the lack of a consensus framework, vague terminology and a multidimensional nature of symptoms. Although subjective methods (e.g. self-reported or parent-reported surveys)(23, 24) are commonly used, they can be distorted by response and recall bias. More objective methods (e.g. polysomnography and performance tests)(25-27) are expensive and time-consuming, and the prevalence of fatigue varies by age group. For example, it is common in infancy, early childhood and late adolescence, while being less frequently observed in mid-childhood, and it is more common in girls than it is in boys.(26) Such variations in fatigue amongst healthy children makes it difficult to quantify fatigue in patients. Fatigue is determined by a variety of factors. In adult studies, active inflammation, depression and other factors are implied in fatigue. A recent review on fatigue in IBD patients classifies factors into two categories: modifiable and non-modifiable.(28) The modifiable factors include physical factors (e.g. disease activity, anaemia, physical functioning and fitness), as well as psychosocial factors (e.g. anxiety, depression and self-directed personality). Non- modifiable factors include disease duration, gender and extra-intestinal manifestations. All studies in the review describe adult patients, and it is unclear whether a similar classification would apply to children with IBD. For this reason, we performed a systematic review of the existing literature aimed at exploring the prevalence of fatigue in paediatric IBD and identifying elements that contribute to fatigue ( Chapter 5 ). Several studies have suggested that disease activity, anaemia and physical functioning affect the experience of fatigue.(24, 29-31) General introduction