A SIMPLE ALGORITHM TO PREDICT THE DEVELOPMENT OF RADIOLOGICAL EROSIONS IN PATIENTS WITH EARLY RHEUMATOID-ARTHRITIS - PROSPECTIVE COHORT STUDY

Objective-To produce a practical algorithm to predict which patients w ith early rheumatoid arthritis will develop radiological erosions. Des ign-Primary care based prospective cohort study. Setting-All general p ractices in the Norwich Health Authority, Norfolk Subjects-175 patient s notified to the Norfolk Arthritis Register were visited by a metrolo gist soon after they had presented to their general practitioners with inflammatory polyarthritis, and again after a further 12 months. All the patients satisfied the American Rheumatism Association's 1987 crit eria for rheumatoid arthritis and were seen by a metrologist within si x months of the onset of symptoms. The study population was randomly s plit into a prediction sample (n = 105) for generating the algorithm a nd a validation sample (n = 70) for testing it. Main outcome measures- Predictor variables measured at baseline included rheumatoid factor st atus, swelling of specific joint areas, duration of morning stiffness, nodules, disability score, age, sex, and disease duration when the pa tient first presented. The outcome variable was the presence of radiol ogical erosions in the hands or feet, or both, after 12 months. Result s-A simple algorithm based on a combination of three variables-a posit ive rheumatoid factor test, swelling of at least two large joints, and a disease duration of more than three months-was best able to predict erosions. When the accuracy of this algorithm was tested with the val idation sample, the erosion status of 79% of patients was predicted co rrectly. Conclusions-A simple algorithm based on three easily measured items of information can predict which patients are at high risk and which are at low risk of developing radiological erosions.