Els van de Vijver

92 with the fatigue-related diagnostic tests mentioned in this paper. The model highlights the importance of the multifaceted nature of fatigue, and this fatigue model could act as a guide on which to base treatment interventions. Biological factors Fatigue is a common finding (6) in children and adolescents with IBD, and several studies have shown a positive relationship between the degree of disease activity and fatigue. Adolescents with active IBD experience more fatigue than their peers in disease remission, who, in turn, experience more fatigue than healthy controls. It is plausible that active disease impairs sleep quality due to nocturnal abdominal pain and diarrhoea. Inflammation and immune activation, together with the subsequent activation of glial cells and mitochondrial damage, likely account for the severe levels of intractable fatigue and disability seen in patients with autoimmune diseases.(19) Adolescents in clinical remission are fatigued, but patients in deep remission were not assessed: deep remission could have an impact on less fatigue. Reduced muscle mass (20) and anaemia (21-23), both of which are frequently observed in patients with IBD, even when their disease is in remission, may also have affect fatigue, but so far, these factors have not been investigated in the adolescent IBD population. Psychobehavioral factors The papers that sought correlations between psychobehavioral factors and fatigue showed conflicting results. One paper (14) linked anxiety, depression and lack of family support with IBD-related fatigue, while another paper failed to show that depression occurs more often in adolescents with IBD than in their healthy peers.(6) Sleep disorders can affect the feeling of being tired, as shown in 2 of the included papers. Sleep deprivation leads to more anxiety and depression and to an increase in somatic complaints and aggressive behavior.(13, 16, 17) Sleep itself was not often a research objective; only one study had sleeping problems as an outcome measurement (16), while a German study only reported a trend towards prolonged sleep duration in patients with mild IBD compared to healthy controls.(8) Chapter 5 92