Investigating the trajectory of functional disability in systemic sclerosis: group-based trajectory modelling of the Health Assessment Questionnaire-Disability Index.

ABSTRACT

OBJECTIVES: To identify the trajectories and clinical associations of functional disability in systemic sclerosis (SSc). METHODS: Australian Scleroderma Cohort Study (ASCS) participants meeting ACR/EULAR criteria for SSc recruited within 5 years of disease onset, with ≥2 Health Assessment Questionnaire-Disability Index (HAQ-DI) scores were included. Group based trajectory modelling (GBTM) was used to identify the number and shape of HAQ-DI trajectories. Between group comparisons were made using the chi-squared test, two-sample t-test or Wilcoxon rank-sum test as appropriate. Multiple logistic regression was used to identify features associated with trajectory group membership. Survival analyses were performed using Kaplan Meier and Cox proportional hazard modelling. RESULTS: We identified two HAQ-DI trajectory groups within 426 ASCS participants with incident SSc low-stable disability (n=221, 52%), and high-increasing disability (n=205, 48%). Participants with high-increasing disability were older at disease onset, more likely to have diffuse SSc (dcSSc), cardiopulmonary disease, multimorbidity, digital ulcers, and gastrointestinal involvement (all p≤0.01), as was use of immunosuppression (p<0.01). Multimorbidity was associated with high-increasing trajectory group membership (OR3.1, 95%CI1.1-8.8, p=0.04); independently, multiple SSc features were also strongly associated including dcSSc (OR2.3, 95%CI1.3-4.2, p<0.01), proximal weakness (OR7.3, 95%CI2.0-27.1, p<0.01) and joint contractures (OR2.7, 95%CI1.3-5.3, p<0.01). High-increasing physical disability was associated with an almost two-fold increased risk of mortality (HR1.9, 95%CI1.0-3.8, p=0.05), and higher symptom burden. CONCLUSIONS: Two trajectories of functional disability in SSc were identified. Those with high-increasing functional disability had a distinct clinical phenotype and worse survival compared to those with low-stable functional disability. These data highlight the pervasive nature of physical disability in SSc, and its prognostic importance.