Derivation and validation of a prediction rule for two-year mortality in early diffuse cutaneous systemic Sclerosis

Objective Systemic sclerosis (SSc) is associated with a reduction in life expectancy, but there are no validated prognostic models for determining short-term mortality. The objective of this study was to derive and validate a prediction rule for 2-year mortality in patients with early diffuse cutaneous SSc (dcSSc). Methods We studied a prospectively enrolled cohort of 387 US Caucasian patients with early dcSSc (<2 years from the appearance of the first symptom), randomly divided into a derivation cohort (n = 260) and a validation cohort (n = 127). Predefined baseline predictor variables were analyzed in a stepwise multivariable logistic regression model in order to identify factors independently associated with 2-year all-cause mortality using a cutoff of P < 0.05. We rounded the beta values to the nearest integer and summed the points assigned to each variable in order to stratify patients into low-risk, moderate-risk, and high-risk groups. We then applied this rule to an external validation cohort of 110 Caucasian patients with early dcSSc from a single UK center and compared stratum-specific mortality using chi-square statistics. Results Four independent predictor variables (with assigned integer values) comprised the model: age at first visit (points allotted: -1, 0, or 1), skin thickness progression rate (points allotted: 0 or 1), gastrointestinal tract severity (points allotted: 0, 1, or 2), and anemia (points allotted: 0 or 2). The prediction model performed well, with no significant differences between the derivation cohort and the US or UK validation cohorts in the low-risk and moderate-risk groups. Conclusion We derived a 4-variable prediction rule that can be used to stratify patients with early dcSSc into groups by risk of 2-year mortality, and we validated that prediction rule in US and UK cohorts.