Modeling the progression of rheumatoid arthritis: A two‐country model to estimate costs and consequences of rheumatoid arthritis

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Abstract
Objective Two simulation models were developed to analyze the cost‐effectiveness of new treatments that affect the progression of rheumatoid arthritis (RA). Methods We used data from 2 cohorts of patients with early RA who had been followed up since disease onset (up to 15 years). In the Swedish study, 183 patients were followed up for a mean of 11.3 years. In the UK study, 916 patients were followed up for a mean of 7.8 years. Disease progression over 10 years was modeled as annual transitions between disease states, defined by Health Assessment Questionnaire (HAQ) scores. A regression model was used to estimate transition probabilities conditional on age, sex, and time since onset of disease, in order to allow simulation of different patient cohorts. Costs and utilities associated with different HAQ levels were based on data from the cohort studies and cross‐sectional surveys. Results Costs increase and quality of life decreases as RA progresses. In Sweden, total annual costs range from $4,900 to $33,000 per patient, compared with $4,900 to $14,600 in the UK. Cumulative costs over 10 years for patients starting in disease state 1 (HAQ < 0.6) are $54,600 in Sweden and $26,600 in the UK. The cumulative numbers of quality‐adjusted life‐years (QALYs) are 5.5 and 5.6, respectively. Both costs and QALYs were discounted at 3%. Conclusion The 2 models, which were based on different patient cohorts, reach a similar conclusion in terms of the effect of RA over 10 years. They appear to accurately capture disease progression and its effects and can therefore be useful in estimating the cost‐effectiveness of new treatments in RA.