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

Objective 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. Conclusion 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.