How to avoid phenotypic misclassification in using joint destruction as an outcome measure for rheumatoid arthritis?

Joint destruction is a measure for RA severity that is accurate, sensitive and reflective of the cumulative disease burden. Risk factors for this outcome measure may be used to arrive at individualized treatment strategies. Currently, relatively few risk factors for joint destruction are known. New risk factors, genetic risk factors in particular, may have relatively small effects on the rate of joint destruction. A sensitive determination of joint damage is then crucial in order to identify these risk factors and will reduce the risk on type 2 errors. The present article addresses the question how the rate of joint destruction is ideally measured. Different methods are discussed and suggestions for corrections of factors that affect the natural course of joint destruction, such as applied treatment strategies, are made. It is concluded that a precise estimation of the rate of radiological joint destruction is obtained by using quantitative and validated scoring methods as well as repetitive measurements over time in order to reduce within patient variation.