Impaired secretion of parathyroid hormone in patients with rheumatoid arthritis: relationship to inflammatory activity.

Hypocalcaemic tests, employing infusion of EDTA over 1 h, were performed in 22 patients with rheumatoid arthritis (RA) and 14 healthy controls. The basal levels of calcium and parathyroid hormone (PTH) were not significantly different in the two groups. The RA patients displayed a markedly impaired PTH response during infusion of EDTA compared with the controls although the reduction of plasma ionized calcium was similar. The PTH response was furthermore significantly, inversely, related to the inflammatory activity measured as sedimentation rate (r = 0.65; P less than 0.01), i.e. the more pronounced the inflammation, the less the capacity to secrete PTH. Since secretion of PTH is related to the intracellular calcium concentration of the parathyroid cells, these findings are in line with previous observations of a higher intracellular calcium content in inflammatory disease. They also support the earlier indications of reduced bone turnover in inflammatory arthritides. An insufficient parathyroid function could be one factor contributing to bone disease in these conditions.