The ups and downs of living with fibromyalgia: A digital diary N-of-1 observational study

Background & Aims The psychological flexibility model builds on cognitive-behavioural principles and provides a theory-based approach to chronic pain treatment. Previous research has evaluated this model primarily using retrospective self-reports of psychological in-/flexibility and group-level analyses, while fluctuations over time and within-person differences remain understudied. This study aims to validate the psychological flexibility model in real-time by determining i) the dynamics of psychological inflexibility in everyday life and ii) if psychological inflexibility predicts well-being and functioning at an individual level in fibromyalgia. The secondary aim is to investigate implications of data imputation techniques when handling missing data in N-of-1 studies. Methods An N-of-1 observational design was used. Six women with fibromyalgia enrolled in the study and were prompted to complete a digital diary twice daily for six weeks assessing psychological inflexibility, well-being (mood, stress, fatigue), and functioning (pain self-efficacy, pain catastrophizing, pain avoidance). Dynamic regression modelling was performed including Bonferroni corrected alpha levels and sensitivity analyses comparing results across three data imputation strategies (single, multiple, no imputations). Results The final dataset included three participants, who completed 54 (64%), 75 (87%), and 76 (88%) assessments, respectively. Psychological inflexibility showed fluctuations over time for all participants, significantly predicted well-being and functioning for two participants (following Bonferroni correction), and between-person differences in strength and significance of associations appeared. Results were sensitive to how missing data was handled. Conclusions The findings demonstrate that psychological inflexibility is measurable in everyday life, revealing its context-sensitive and time-dependent nature. Psychological inflexibility appears to predict within-person well-being and functioning in everyday life, which suggests it as a key change mechanism in pain treatment. Future research with a similar design is warranted to replicate and validate these findings.