Background Radiological progression is considered the most important outcome for Rheumatoid Arthritis, but there is no established definition, as to what constitutes a clinical important progression of joint damage. The smallest detectable difference (SDD) for the modified Sharp method and the Larson method was taken as a starting point. And expert opinion of rheumatologists was used to determine the clinical relevant progression. However these findings might not reflect the true clinical important progression in radiological damage. The clinical important difference should be the effect this progression has on the patient, being the development of physical disability.
Objectives To estimate the clinical relevant increase in radiological damage, using the effect on physical disability.
Methods This study elaborates on the findings of studies, investigating the clinical relevant increase in the HAQ-DI score, and on a study investigating the relation between disease activity, radiological damage, sociodemographic factors, and physical disability. The clinical relevant difference in physical disability (HAQ-DI) has been determined by asking patients to rate themselves relative to another patient, and was estimated to be between 0,2 and 0,3. The relation between physical disability (HAQ-DI), disease activity (DAS), and radiological damage (Modified Sharp score) was determined, using the follow-up data of 378 patients from an open prospective study of early RA (disease duration < 1 year). Linear regression was used at 0, 3, 6, and 9 years after inclusion with as dependant variable the HAQ-DI, and as independent variables, disease activity (DAS), radiological damage, and sociodemographic factors. The main results of this study were that the relation between radiological progression and physical disability was dependent on the activity of the disease and the present radiological damage (5). With higher disease activity, or more damage present the effect of radiological damage on physical function decreased. Using the derived linear regression models and the measure of a clinical relevant difference in HAQ-DI a clinical relevant increase in radiological damage for the modified Sharp score was calculated.
Results The clinical relevant increase in radiological damage was estimated to be about 10 or 20, for a DAS of 1 or 2 respectively. It was dependant on the activity of the disease and amount of existing joint damage.
Conclusion Estimating a clinical relevant increase in radiological progression, using the patient’s perspective is possible. A conservative threshold of 10–20 for a clinical relevant increase (Modified Sharp score) can be used as a guideline. These results need replication in other patient cohorts.
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