Objective: To measure the change in bone mineral density (BMD, g/cm2) in a female population with systemic lupus erythematosus (SLE) over 3 years, to identify factors predictive of bone loss, including the role of corticosteroid and disease related variables, and to determine the predictive value of urinary collagen crosslinks for bone loss.
Methods: All premenopausal women with SLE who participated in a cross sectional study of BMD in 1994 were invited to undergo a standardized interview, examination, medical record review, and BMD measurement of the lumbar spine and femoral neck by dual energy x-ray absorptiometry.
Results: Thirty-two women participated with a mean (SEM) age of 35.2 (1.5) years, duration of SLE of 7.0 (0.8) years, and mean (range) time to followup of 3.2 (2.9-3.4) years. Twenty-one subjects were exposed to corticosteroids during the study period with a mean (range) daily dose of prednisolone of 11.1 (2.8-22.9) mg. There was no significant change over the 3 years in BMD at the lumbar spine (1.161+/-0.122 vs. 1.169+/-0.022; p = 0.39) or femoral neck (0.944+/-0.023 vs. 0.955+/-0.020; p = 0.47) for the group as a whole, or when subjects were divided according to corticosteroid exposure. However, in the corticosteroid exposed subgroup, patients treated with > or = 7.5 mg/day (n = 14) lost lumbar spine BMD (-0.50%/yr) in contrast to those receiving <7.5 mg/day, who gained 1.06%/yr (p = 0.02). Furthermore, no participant receiving <7.5 mg/day lost lumbar spine BMD, while 57% of patients receiving > or =7.5 mg/day lost lumbar spine BMD (p = 0.01). In the corticosteroid exposed subgroup only, subjects who did not exercise regularly lost femoral neck BMD, while those who did gained femoral neck BMD (-0.54%/yr vs. 1.39%/yr; p = 0.02). Disease related variables (disease severity, activity, duration, functional capacity) and baseline urinary collagen crosslink levels were not predictive of BMD change.
Conclusion: Loss of lumbar spine and femoral neck BMD in this premenopausal female SLE population was minimal for the group as a whole; however, a daily dose of prednisolone of > or =7.5 mg was associated with loss of lumbar spine BMD. In corticosteroid exposed patients, regular exercise was protective of femoral neck BMD loss. A single baseline measurement of urinary collagen crosslinks was not predictive of bone loss.