To assess disability in systemic sclerosis (SSc) longitudinally and to identify disease-specific determinants, after accounting for informative patient dropout.
We performed a multicenter, longitudinal study of 745 patients with SSc followed in the Canadian Scleroderma Research Group registry. Disability was assessed using the Health Assessment Questionnaire (HAQ). Longitudinal changes in disability were modeled using statistical approaches accounting for various levels of patient dropout.
In all the models, disability in SSc worsened over time. The magnitude of the worsening was small when patient dropout was assumed to be completely at random (increase in the HAQ of 0.022, 95% CI 0.002-0.042, per year). After accounting for different levels of informative patient dropout, the increase in the HAQ ranged from 0.039 (95% CI 0.018-0.061) per year to 0.071 (95% CI 0.048-0.094) per year. Thus, using the most conservative of these estimates, this was equivalent to an increase in the HAQ of 0.12 over 3 years. The disease correlates found to be most closely associated with disability were diffuse disease and breathing problems.
Our study provides strong evidence that SSc causes increased disability over time, with breathing problems and disease type being the strongest predictors of disability. Statistical modeling accounting for informative patient dropout is necessary to properly assess the outcomes of patients followed longitudinally.