Advances in Inflammation Research, Vol. 3: Rheumaîoid Arthntis, ediled by S. Gorini et al. Raven Press. New York © 1982. R égional Bone Calcium Turnover Rate in Rheumatoid Arthritis: Comparison with the Disease Activity *P. Bergmann, *D. Mannicourt, *P. Martin, **S. Orloff, and *A. Schoutens *Department of Nuclear Medicine and **Rheumatology, Brugmann University Hospital, Brussels Free University, 4 Place Van Gehuchten, 1020 Brussels, Belgium The synovial tissue in rheumatoid arthritis (RA) is characterized by an intense lymphocytic and inflammatory cell infiltration (16). This infiltrate spreads over the surface of the articular cartilage and leads, through the médiation of proteases, collagenases, and mechanical factors to cartilage and bone résorption, with periar ticular osteoporosis, bone érosion, and narrowing of the joint space. The periarticular bone is hyperactive at bone scintigraphy (5). Some investigators, on the basis of quantitative bone scan (15) and of skeletal density measurements (14) have suggested that the increased bone remodeling is not confined to the periarticular areas, but concerns also nonjoint bone. The aim of this study was to investigate the effect of RA on the bone turnover rate, near the joints and in the whole body. We measured in 13 patients with séropositive RA the régional bone calcium accretion rate and exchangeable pool (2) and the 24hr whole body rétention of 99m Te pyrophosphate (12). The results were compared with the foUowing clinical and biological data: The sérum alkaline phosphatase (SAP), the urinary hydroxyproline, the joint count (JC), the erythrocyte sédimentation rate (ESR), the Creactive protein (CRP), and the plasma level of Pjmicroglobulin. MATERIALS AND METHODS Régional and Total Body Calcium Accretion Rate and Exchangeable Pool (2) Fifty fjiCi of'''CaClj (I.R.E., Fleurus  S.A. > 200 (jiCi/mg Ca) were calibrated and injected intravenously. Blood was drawn at 1,4, 24, 48, 72, 96, 144, 192, and 240 hr thereafter, and the '•''Ca activity of 4 ml of sérum was measured with a Packard automatic gamma counter. The sérum calcium was measured on the same samples by atomic absorption spectrometry (Perkin Elmer 305 B). We calculated 303