Serum osteocalcin and calcitropic hormones in a homogeneous group of patients with rheumatoid arthritis: its implication in the osteopenia of the disease.

Different mechanisms may play a role in the pathogenesis of the generalized osteopenia found in rheumatoid arthritis (RA). We measured the calcium, osteocalcin (BGP), parathyroid hormone (PTH), calcitonin (CT) and 25(OH)D3 levels as well as urine 24 hr calcium, Ca/Cr and OHP/Cr in a homogeneous group of 30 non-disabled patients (10 men, 8 premenopausal women and 12 postmenopausal women) recently diagnosed as having RA (disease duration 4 to 6 months). They had normal serum levels of vitamin K, were not on previous or present treatments known to interfere with calcium metabolism, and were not pregnant if females of fertile age. The group was compared with an age-matched control group of 32 healthy subjects (10 men, 8 premenopausal women and 14 postmenopausal women). We observed significantly decreased levels of 25(OH)D3 (29.9 +/- 9.9 vs 48.7 +/- 12.1 ng/mL; p < 0.005) and significantly increased levels of urine OHP/Cr (2.24 +/- 0.71 vs 1.56 +/- 0.82 mg/mg; p < 0.001) in the RA group. No differences in these two parameters were found between the three subgroups of RA patients. Male RA patients showed decreased levels of serum BGP (7.3 +/- 1.0 vs 8.2 +/- 1.7 ng/mL; p < 0.01). The remaining parameters did not differ significantly between RA patients and controls. These data suggest that the generalised osteopenia found in RA may be a consequence of increased bone resorption without a concomitant increase in bone formation, perhaps related to mechanisms inherent to the disease.