Within-person fluctuations of fatigue in patients with a clinical diagnosis of systemic sclerosis and its relationship with mood, pain, sleep and physical activity.

Objectives: To explore the within-person fluctuations of fatigue in systemic sclerosis and its association with negative affect, positive affect, pain, perceived exertion of physical activity and quality of sleep.

Methods: We performed an ecological momentary assessment study in adult patients with a clinical diagnosis of systemic sclerosis. During 14 days, patients completed daily assessments of fatigue severity, negative affect, positive affect, pain, quality of sleep and perceived exertion of physical activity at four fixed time points. The day-to-day fluctuations in fatigue were quantified by the intra-individual variance and probability of acute change, capturing the magnitude and frequency of clinical relevant within-person day-to-day fluctuations, respectively. Using multilevel models, the within-person association between fatigue and the daily assessments were analysed.

Results: Fifty-seven patients with systemic sclerosis participated. The mean (standard deviation) intra-individual variance was 1.08 (0.42) and the probability of acute change was mean (standard deviation) 0.40 (0.14), ranging from 0.08 to 0.77. For fatigue, a within-person variation of 51% was observed. Multilevel analyses showed that higher average levels and daily increases in negative affect, pain and perceived exertion of physical activity were associated with more fatigue, while the opposite was observed for positive affect and quality of sleep. Positive affect demonstrated the strongest association with fatigue fluctuations.

Conclusion: This is the first quantitative study showing that fatigue in systemic sclerosis is characterized by a dynamic course and that approximately half of the day-to-day fluctuations within persons are clinically meaningful. Furthermore, our results indicate that integrating activities with positive impact on mood into fatigue treatment strategies might reduce the frequency of fatigue fluctuations.