To investigate the long-term radiographic course as a mathematical function of disease duration in individual patients and in a group of patients with rheumatoid arthritis (RA).
In 109 patients with RA, radiographic examinations of 46 diarthrodial joints were performed at regular intervals of 1-3 years, for up to 30 years after disease onset.
Five main types of progression were identified: 1) a rare type (<1%), with no radiographic progression at all; 2) a type with a slow or moderate onset, but an increasing progression rate (9% exponential growth type and 30% linear type); 3) a type with a moderate-to-fast onset and a stable progression rate (the square-root type; 11%); 4) a type with a fast onset, but a later decreasing progression rate (the first-order kinetics type, 30%); and 5) a type characterized by slow onset, then acceleration and later deceleration (the sigmoid type, 20%).
The progression of radiographic damage in RA followed mathematical functions of time. The identification of progression type may be used in the prediction of outcome in patients with RA.