Bone mineral density and urolithiasis interaction in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory disease with extraarticular manifestations involving many organs. Both urinary stone formation and bone mineral density (BMD) can be affected by calcium (Ca) metabolism changes in RA. We aimed, in our study, to investigate the incidence of urolithiasis in adult RA patients and to identify the BMD characteristics of stone-forming RA patients. Seventy-nine RA patients and 35 control subjects participated in our study. None had a known renal disease, except for urolithiasis. Complete blood count (CBC), erythrocyte sedimentation rate (ESR), rheumatcoid factor (RF), and C-reactive protein (CRP) were recorded. Twenty-four-hour urinalysis, as well as plain X-ray, ultrasound imaging, and BMD measurements with dual-energy X-ray absorptiometry (DEXA) were performed. T scores more than 1 SD below the mean value were accepted as low BMD. There was no statistically significant difference between urinary stone incidence in RA patients and controls. There was a significant difference between BMD values in RA patients with and without urinary stone disease. The low T scores of stone-forming RA patients may be explained by the additive effect of two coexisting diseases, both shown to be related to low bone mass. From another point of view, both BMD loss and urolithiasis can be consequences of altered Ca metabolism in RA. So we suggest that RA patients with urolithiasis should be evaluated for BMD, and that RA patients with low BMD be evaluated for urolithiasis.