To Örebro University

Background: Systemic lupus erythematosus (SLE) can result in impaired daily physical function through various mechanisms including active disease, chronic damage, and mental health symptoms that are common in the disease. However, the key drivers of reduced physical function are poorly understood, and no large-scale global studies investigating this have been conducted to date.

Objectives: To investigate key factors that contribute to impaired physical function in SLE globally.

Methods: SLE patients were identified from the COVAD 2 database, a global register of more than 20,000 respondents. Healthy controls (HC) were included to compare differences in physical function using the Patient Reported Outcome Measurement Information System (PROMIS) questionnaire. Demographics, medication, comorbidities, disease activity, Global Physical Health (GPH) and Global Mental Health (GMH) were collected. Multivariable regression analysis was used to identify contributing factors to favourable or poor physical function (measured by PROMIS Physical Function shortform PF-10a score).

Results: 979 SLE patients and 3358 HCs were included in analysis. Patients with SLE had significantly lower PF-10a score as compared to HCs (median 42, IQR 36-47 vs median 49, IQR 45-50, p<0.0001). Determinants of physical function status in patients with SLE are summarised in Table 1. Briefly, factors associated with poor physical function included increasing age (-0.042, 95% CI -0.069 to -0.015, p=0.002) and methotrexate use (-0.928, 95% CI -1.844 to -0.012, p=0.047). Diabetes (-1.862, 95% CI -3.481 to -0.243, p=0.024) and interstitial lung disease (ILD) (-2.441, 95% CI -4.366 to -0.517, p=0.013), but not asthma or COPD, also contributed to lower PF-10a score. From a mental health perspective, anxiety (-0.970, 95% CI -1.853 to -0.087, p=0.031) but not depression contributed to a lower physical function score. Higher Pain Visual Analogue Scales (VAS) (-2.889, 95% CI -3.107 to -2.671, p<0.001) and Fatigue VAS (-1.459, 95% CI -1.974 to -0.945, p<0.001) also contributed to lower PF-10 scores. Hydroxychloroquine use (0.844, 95% CI 0.190 to 1.498, p=0.012) and higher GPH score (2.287, 95% CI 2.079 to 2.494, p<0.001) were associated with favourable physical function.

Conclusion: Patients with SLE show significantly reduced physical function compared with HCs. Key contributors to poor physical function include intercurrent diabetes and ILD. Screening for, and aggressive early treatment of these conditions may confer improved long-term function. As expected, higher levels of pain and fatigue were associated with poor physical function. Methotrexate use was also identified as a contributing factor to reduced function, which could represent its use in articular manifestations that limit physical function. Importantly, use of hydroxychloroquine was associated with favourable physical function, adding to the well-recognised benefits of this drug in SLE.