Cost of illness in rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis and systemic lupus erythematosus in Germany

Objective: To estimate and compare the direct and indirect costs of illness in rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis (PsA) and systemic lupus erythematosus (SLE), and to evaluate the effect of sex, disease duration and functional status on the various cost domains. Methods: Data of outpatients, aged 18 - 65, with rheumatoid arthritis (n = 4351), ankylosing spondylitis (n = 827), PsA ( n = 908) or SLE ( n = 844), who were enrolled in the national database of the German collaborative arthritis centres in 2002, were analysed. Data on healthcare consumption, out-of-pocket expenses and productivity losses were derived from doctors and patients. For the calculation of indirect costs, the human capital approach (HCA) and the friction cost approach (FCA) were applied. Results: Mean direct costs amounted to EURO4737 a year in rheumatoid arthritis, EURO3676 in ankylosing spondylitis, EURO3156 in PsA and EURO3191 in SLE. By using the HCA, total costs were calculated at EURO15 637 in rheumatoid arthritis, EURO13 513 in ankylosing spondylitis, EURO11 075 in PsA and EURO14 411 in SLE, whereas with the FCA the numbers were EURO7899, EURO7204, EURO5570 and EURO6518, respectively. Costs increased with disease duration and were strongly dependent on functional status. In patients with the highest disability (< 50% of full function), the total costs on applying the HCA were EURO34 915 in rheumatoid arthritis, EURO29 647 in alkylosing spondylitis, EURO37 440 in PsA and EURO32 296 in SLE. Conclusion: The costs of illness are high in all four diseases, with a strong effect of functional status on total costs. Indirect costs differ by the factor 3, based on whether the HCA or the FCA is used.