Dual trajectories of fatigue and disease activity in an inception cohort of adults with systemic lupus erythematosus over 10 years.

Objectives: Fatigue is one of the most common symptoms reported in patients living with SLE. We aim to: 1) determine if different trajectories of fatigue associate with specific latent classes of disease activity and 2) define the patient characteristics and associated factors in different latent classes.

Methods: Data from an inception cohort of adult patients from the Toronto Lupus Clinic from 1997-2018 were analyzed. Fatigue levels were measured using Fatigue Severity Scale (FSS) and disease activity by the Adjusted Mean Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) (AMS). Dual latent class trajectory analysis, for fatigue and AMS, was performed. Univariable and multivariable logistic regression analyses assessed the association of baseline variables with class membership.

Results: Among 280 patients, 4 dual classes (C) of fatigue and disease activity were identified: C1- lowest disease activity and second highest fatigue trajectory (27%); C2- second highest disease activity and highest fatigue trajectory (30%); C3-moderate disease activity and lowest fatigue trajectory (33%); and C4- highest disease activity and moderate fatigue trajectory (10%).

Conclusion: 4 distinct latent classes of dual fatigue and disease activity trajectories were identified. Fatigue and disease activity follow distinct trajectories and disease activity alone cannot fully explain fatigue trajectories. Trajectories with higher FSS scores were associated with more fibromyalgia and trajectories with higher disease activity were associated with higher cumulative glucocorticoid use. Higher baseline glucocorticoid use was more likely associated with more fatigue while older age at SLE diagnosis was associated with less fatigue.