Are disease duration and degree of functional impairment determinants of bone loss in rheumatoid arthritis?

One hundred and five patients with rheumatoid arthritis treated with a variety of antirheumatic drugs, excepting glucocorticoids, were stratified according to the degree of functional impairment (functional classes I to IV) and duration of the disease (0-3 years; 4-8 years; and greater than 8 years). The variables investigated were distal forearm bone mineral content (BMC), biochemical markers of bone formation: serum alkaline phosphatase and serum bone gamma-carboxyglutamic acid containing protein (BGP) and biochemical markers of bone resorption: fasting urinary calcium and fasting urinary hydroxyproline. Significant relationships were found between BMC and functional impairment and duration of the disease. Indices of bone formation and bone resorption rose with increasing functional impairment, particularly those of bone resorption. It is concluded that disability induces osteopenia in rheumatoid arthritis by increasing the bone turnover with a more marked increased in resorption than in the formation processes. The effect of the disease duration is merely that of adding more years of functional impairment.