Fatigue, patient reported outcomes, and objective measurement of physical activity in systemic lupus erythematosus

Objective: Fatigue is a common symptom in systemic lupus erythematosus (SLE), and engaging in physical activity may reduce fatigue. We aimed to characterize relationships between fatigue, other health status measures assessed with the Patient Reported Outcomes Measurement Information System (PROMIS) instruments, and accelerometer-based physical activity measurements in patients with SLE. The internal consistency of each PROMIS measure in our SLE sample was also evaluated.

Methods: This cross-sectional study analyzed 123 adults with SLE. The primary fatigue outcome was Fatigue Severity Scale score. Secondary outcomes were PROMIS standardized T-scores in seven health status domains. Accelerometers were worn for seven days, and mean daily minutes of light, moderate/vigorous, and bouted (10 minutes) moderate/vigorous physical activity were estimated. Cronbach's alpha was determined for each PROMIS measure to assess internal consistency. Relationships between Fatigue Severity Scale, PROMIS, and physical activity were summarized with Spearman partial correlation coefficients (r), adjusted for average daily accelerometer wear time.

Results: Mean Fatigue Severity Scale score (4.3, SD 1.6) was consistent with clinically relevant levels of fatigue. Greater daily and bouted moderate/vigorous physical activity minutes correlated with lower Mean Fatigue Severity Scale score (r = -0.20, p = 0.03 and r = -0.30, p = 0.0007, respectively). For PROMIS, bouted moderate/vigorous physical activity minutes correlated with less fatigue (r = -0.20, p = 0.03). PROMIS internal consistency was excellent, with Cronbach's alpha > 0.90 for each domain. Mean PROMIS T-scores for fatigue, pain interference, anxiety, sleep disturbance, sleep-related impairment, and physical function were worse than reported for the general US population. More moderate/vigorous physical activity minutes were associated with less pain interference (r = -0.22, p = 0.01). Both light physical activity and moderate/vigorous physical activity minutes correlated with better physical function (r = 0.19, p = 0.04 and r = 0.25, p = 0.006, respectively).

Conclusion: More time spent in moderate/vigorous physical activity was associated with less fatigue (Fatigue Severity Scale and PROMIS), less pain interference, and better physical function (PROMIS). PROMIS had excellent internal consistency in our SLE sample, and six of seven PROMIS measures indicated poorer average health status in SLE patients compared with the general US population.