Day-to-day fluctuations of fatigue severity in individuals with knee osteoarthritis: an ecological momentary assessment approach

Lay Summary What does this mean for patients? Pain is the most commonly experienced symptom in OA. However, nearly half of the individuals report fatigue as well. The variable and unpredictable course of fatigue adds to the disease burden of OA, including pain, stiffness and functional limitations. Yet the ups and downs of fatigue severity have been poorly understood. For 14 days, individuals filled in daily questions about fatigue, pain, feeling happy and relaxed, feeling depressed and stressed, sleep and perceived exertion of physical activity on a smartphone. We found that some individuals with knee OA showed almost stable levels of fatigue severity, while others experienced many fatigue variations. When individuals reported more fatigue than usual, they also experienced more pain, felt less happy and relaxed or felt more depressed and stressed than usual. A night of worse sleep or a day of more perceived exertion of physical activity was not associated with more fatigue that same day. Thus pain, feeling happy and relaxed or depressed and stressed are likely to add to the daily variations of fatigue severity. Targeting these factors may help to lessen the burden of fatigue and its variable course. Objective The variable course of fatigue adds to the disease burden of patients with OA yet it has been poorly understood. This study aimed to describe within-person fluctuations of fatigue severity and explore its associations with pain, positive affect, negative affect, sleep, and perceived exertion of physical activity. Methods Individuals with chronic knee pain or a clinical diagnosis of knee OA & GE;40 years of age completed daily assessments about fatigue, pain, positive affect, negative affect, sleep, perceived exertion of physical activity (numeric rating scale 0-10), and overwhelming fatigue (yes/no) on a smartphone over 14 days. Within-person fluctuations of fatigue severity were described by the probability of acute changes (PACs) and s.d.s. Associations with pain, positive affect, negative affect, sleep, and perceived exertion of physical activity were explored using multilevel models. Results Forty-nine individuals were included (mean age 63.4 years; 82% female). PACs and s.d.s of within-person daily fatigue fluctuations ranged from 0.00 to 0.80 and 0.35 to 2.95, respectively. Within-person associations of fatigue severity were moderate for positive affect [& beta; = -0.57 (95% CI -0.67, -0.47)], weak for pain [& beta; = 0.41 (95% CI 0.29, 0.53)] and negative affect [& beta; = 0.40 (95% CI 0.21, 0.58)], and negligible for sleep [& beta; = -0.13 (95% CI -0.18, -0.08)] and perceived exertion of physical activity [& beta; = 0.18 (95% CI 0.09, 0.26)]. Conclusion Some individuals showed almost stable day-to-day levels of fatigue severity, whereas others experienced a substantial number of clinically relevant fluctuations. To reduce the burden of daily fatigue fluctuations, our results suggest that pain, positive and negative affect rather than sleep and perceived exertion of physical activity should be considered as potential targets.