The impact of disease activity, treatment and disease severity on short-term costs of systemic lupus erythematosus.

OBJECTIVE

To assess the impact of disease activity, current treatment, and global disease severity (or damage) on short-term direct and indirect costs of systemic lupus erythematosus (SLE).

METHODS

150 patients were evaluated twice, one year apart. Disease activity was assessed by the SLE disease activity index, and ordinal scales were used to evaluate treatment (prednisone = 0, 1 to 20 mg/day, > 20 mg/day, and use of immunosuppressive agents) and global disease severity [renal severity = 0 to 3, central nervous system (CNS) severity = 0 to 2, hematologic severity = 0 to 1]. Costs were assessed with the economic portion of the Health Assessment Questionnaire adapted for Canada.

RESULTS

Global disease severity was significantly correlated with both direct (p = 0.0001) and indirect (p = 0.02) costs, and current treatment with indirect costs (p = 0.002). The renal and CNS subscales of the global severity measure predicted direct costs (p < 0.01) and the CNS subscale predicted indirect costs (p = 0.002). Stepwise multivariable models selected the global severity index (p = 0.004) as a predictor of direct costs, and either the treatment index (p = 0.02) or the global severity index (p = 0.02) as a predictor of indirect costs.

CONCLUSION

The global disease severity index, particularly the subscales involving the renal and CNS organ systems, and the treatment index are predictors of the short-term costs of SLE.