Reduced disability at five years with early treatment of inflammatory polyarthritis - Results from a large observational cohort, using propensity models to adjust for disease severity

Objective. To determine the effect of treatment with disease-modifying anti rheumatic drugs (DMARDs) and/or steroids on 5-year disability outcome in pa tients with inflammatory polyarthritis. Methods. Three hundred eighty-four patients registered by the Norfolk Arthr itis Register (a primary care-based observational cohort) were followed up for 5 years. Treatment details and Health Assessment Questionnaire (HAQ) sc ores were recorded annually. Logistic regression was used to model differen ces in baseline factors associated with the start of DMARDs and/or steroids within 12 months of baseline. Based on this model, each subject was given a probability of starting treatment ("propensity score"). A second model co mpared the odds of disability (HAQ score greater than or equal to1.00) in t reated and untreated patients, adjusting for differences in disease severit y using the propensity score. Results. Unadjusted analysis suggested that patients who received treatment had an increased odds of a worse outcome compared with those who did not r eceive treatment. When adjusted for differences in disease severity, using the propensity score, early treatment (within 6 months of symptom onset) wa s associated with a similar odds of disability at 5 years com-pared with th ose not treated (odds ratio 0.71; 95% confidence interval 0.34, 1.44). In c ontrast, starting treatment later (greater than or equal to6 months) was as sociated with a 2-fold increased odds of having a HAQ score greater than or equal to1.00 at 5 years. Conclusion. The propensity score was a useful method of adjusting for "conf ounding by indication" in observational studies. Furthermore, this study sh owed that early treatment with DMARDs/steroids (within 6 months of symptom onset) reduced the odds of disability 5 years later to a level comparable w ith that of patients judged clinically as not requiring treatment.