Background/Purpose:

For patients with SLE, disease status, physical functioning, and participation in daily activities affect health-related quality of life. This study aims to: 1) describe physical functioning and disease activity trajectories over time; 2) determine latent classes of different physical functioning and disease activity trajectory combinations; 3) identify membership predictors of these latent classes.

Methods:

This retrospective longitudinal study used single centre inception adult patient data. Physical functioning was measured using patient-reported annual Medical Outcomes Study Short Form 36 (SF-36). Only the physical component summary (PCS) scale was used. Patients with ≥2 SF-36 questionnaires, within the first 2 years of diagnosis, were studied. Disease activity was measured by adjusted mean SLEDAI-2K (AMS) for the year, measured annually. Latent class trajectory modelling was used to combine PCS and AMS trajectories. Models with 2-6 classes were examined. The best model was determined by a combination of clinical and statistical interpretability. The nature of the different classes was explored by examining for annual distribution of clinical features, damage (SDI), cumulative glucocorticoid (GC) dose, and fibromyalgia presence.

Results:

Out of 826 inception patients, 222 were analyzed. Data up to 10 years after diagnosis was examined. Mean age at SLE diagnosis was 35.5 ± 13.2 years. 5 latent classes was the best fit (Figure 1). The 5 classes are: 1) low PCS, very low disease activity (18.9%); 2) high PCS, very low disease activity (17.1%); 3) very low PCS, moderate disease activity (25.3%); 4) high PCS, moderate disease activity (29.7%); and 5) low PCS, high disease activity (9%). More patients in classes 1 and 3 (low to very low PCS) had fibromyalgia than other classes, suggesting this affected their PCS rather than disease activity. Although less class 5 patients had fibromyalgia, more still had this compared to those in classes 2 and 4 patients. 

Class 1 had more activity in CNS and skin systems, more damage, and higher cumulative GC dose (30.2±8.2 vs 20.7±8.7 grams) compared to class 2. Class 3 had more activity in skin and musculoskeletal systems, more damage, and more GCs (38.0 ± 17.9 vs 29.2 ± 11.5 grams) compared to class 4. Class 5 had significant vasculitis and renal involvement, damage, and the highest cumulative dose of GCs.

Conclusion:

There are 5 distinct classes of combined physical component summary scale and disease activity. PCS trajectories seemed more related to the presence of fibromyalgia, except in those with the most severe disease (vasculitis and renal). Identification of comorbid fibromyalgia and targeted supportive measures may help improve the physical component summary scale of 44% (class 1+ 3) of SLE adults.