Management of persistent fatigue: No individual acts like a group

Fatigue has been defined as "extreme tiredness resulting from physical or mental exertion or illness." When severe, it becomes persistent and unrelieved by rest, negatively impacting the physical, social, and academic functioning, as well as the mental well-being of adolescents with chronic health conditions. Since there is no cure for persistent fatigue, treatment focuses on symptom management. This thesis explored self-management strategies to address persistent fatigue in adolescent and young adult patients.

The thesis introduces methodological innovations, such as the Permutation Distancing Test (PDT) and the pediatric Short Fatigue Questionnaire (pSFQ). The primary focus is on 60 adolescents and young adults diagnosed with Q fever Fatigue Syndrome (QFS), Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), post-COVID-19 condition (PCC), and Juvenile Idiopathic Arthritis (JIA). Two self-management strategies were investigated: personalized lifestyle advice and generic dietary advice. The effectiveness of these strategies was evaluated through a randomized cross-over trial (RCT) at the group level and a multiple single-case observational design (SCOD) at the individual level, including Experience Sampling Methodology (ESM) to capture real-time data on fatigue experiences. The hypothesis was that personalized lifestyle advice would be more effective, given the diverse biopsychosocial factors contributing to fatigue among participants, which can be directly addressed through tailored advice.

The RCT results showed that both personalized lifestyle advice and generic dietary advice were equally effective on average in improving fatigue severity, self-efficacy, and quality of life. Although the improvements among participants were small, they were significant and sometimes clinically relevant. These findings suggest that self-management advice could be beneficial during the waiting period for more intensive, guided therapies. Importantly, the analysis of SCOD data revealed variability in individual outcomes, illustrating that what works at the group level does not necessarily translate to the individual level. Improvements were more frequently observed among participants who adhered to personalized lifestyle advice, particularly for those with relatively less severe symptoms and higher levels of self-efficacy.

The thesis also investigated disrupted biological factors across all patient groups. Previous research showed that acute cortisol levels are lower in patients with ME/CFS compared to control groups. However, it is uncertain whether long-term cortisol levels, as measured through hair samples, are similarly affected. During the RCT, hair samples were collected from all patients as well as from a control group. The analysis revealed that long-term cortisol levels were significantly lower in patients with ME/CFS and QFS compared to the control group, and possibly in PCC as well. No significant differences were observed in patients with JIA.

In conclusion, this thesis advocates for a personalized approach to managing persistent fatigue. Future research should continuously investigate the use of self-management interventions, the clinical implementation of ESM, and the biomedical aspects of persistent fatigue in young populations.