Background. Fatigue is a common problem in pediatric rheumatic diseases and is associated with poor quality of life. However, no validated methods are available to measure fatigue in adolescents with familial Mediterranean fever (FMF). The aim of the study was to establish validity and reliability for the child self-report PedsQL Multidimensional Fatigue Scale (PedsQL-MFS) and to investigate the effects of physical characteristics, diseaserelated characteristics, sleep quality/duration, and the amount of physical activity on fatigue in adolescents with FMF.

Methods. Seventy-one adolescents with FMF (13-18 years) were included. Children were examined regarding physical- and disease-related characteristics and completed patient-reported outcome measures (PROMs) regarding sleep quality/duration, physical activity levels, and fatigue. PedsQL-MFS was re-completed within the following 7-14 days.

Results. PedsQL-MFS demonstrated excellent test-retest reliability (ICC in 95% CI: 0.877-0.958) and internal consistency (Cronbach`s α: 0.928). All items contributed to the total score (item-total correlation > 0.3). PedsQLMFS scores were significantly correlated to fatigue (r: -0.666, p < 0.001), physical activity (r: 0.373, p < 0.001), sleep quality (rs: 0.678, p < 0.001), and sleep duration (r: 0.473, p < 0.001). Being female, having attacks in the last six months, a sleep duration of less than seven hours, and engaging in less physical activity resulted in higher fatigue.

Conclusions. PedsQL-MFS seems to be feasible for assessing fatigue in adolescents with FMF. Sex, recent attacks, sleep, and physical activity should be taken into consideration in the fatigue management of patients with FMF.

Keywords: Fatigue, child, familial Mediterranean fever, physical activity, sleep