Osteocalcin and bone mineral content in rheumatoid arthritis

Abnormal bone metabolism was reported in rheumatoid arthritis (RA). In order to evaluate the interest of serum osteocalcin, also called bone GLA-protein (BGP), to assess bone metabolism in RA, we studied 20 postmenopausal RA out-patients and 20 matched controls. Nine patients were treated with low-dose corticosteroids (C+) for at least one year (less than 10 mg/day, prednisolone equivalent), the remaining 11 (C-) received non-steroidal anti-inflammatory drugs (NSAID). The distal and proximal forearm bone mineral content (BMC) was measured by single photon absorptiometry, the vertebral BMC was measured by dual photon absorptiometry. A trend to low BGP was observed in the C+ group. The lowest values were observed in patients with vertebral fractures. Compared with controls, both RA groups had similar low significant BMC at the forearm sites. At the vertebral sites, the bone mineral content decrease observed in the two groups, was more marked in the C+ group. From our results, BGP did not appear as a useful index of osteoporosis in RA, except in some patients with vertebral fractures, treated with low-dose corticosteroids.