Bone and stone in ankylosing spondylitis: osteoporosis and urolithiasis

Ankylosing spondylitis (AS) has well-defined renal complications, but urolithiasis has not been studied in detail. We aimed to evaluate the relation between AS and urolithiasis presence and the effect of this coexistence on the bone mineral status of patients. By dual-energy x-ray absorptiometry measurements at the femoral neck and lumbar vertebrae, we assessed the influence of urolithiasis, disease activity, and duration on bone mineral density (BMD) at different sites. Fifty-three AS patients and 25 control subjects were enrolled in the study. Mean age was 39.49+/-13.01 years for the AS group and 43.80+/-10.69 years for the control group, with no statistically significant difference. Patients were accepted as having active disease if two of the following were present: (1) symptomatic peripheral arthritis, (2) erythrocyte sedimentation rate greater than 30 mm/h, (3) C-reactive protein greater than 5 mg/L, and (4) dorsal-lumbar morning stiffness more than 60 min. The ratios of urinary stone presence were 11.32 and 12% for AS and control groups, respectively. We observed that a statistically significant difference in femur neck BMD between AS patients with or without urolithiasis was apparent. The lumbar BMD values were also lower in the urolithiasis subgroup but could not reach the statistical significance. There were no significant BMD alterations in the control group due to stone presence. Comparison of active-inactive disease groups revealed significantly low T scores in either the femur neck or L2-4 regions of patients with higher activity indices, but this difference was more prominent in the femur neck. In the early AS group (23 patients), 18 patients (78.26%) had L2-4 T scores lower than -1 SD, and in the advanced AS population, 19 of 30 patients (63.33%) had either osteopenia or osteoporosis (OP). We conclude that severe disease and concomitant urolithiasis might increase bone loss and fracture risk especially at the femur neck.