Determinants of bone mass in systemic lupus erythematosus: a cross sectional study on premenopausal women

To evaluate bone mineral density (BMD) in young ambulatory female patients with systemic lupus erythematosus (SLE) and to assess the influence of disease related variables and use of corticosteroids.

Lumbar and femoral BMD were measured by dual x-ray absorptiometry (DXA) in 84 premenopausal patients with SLE (age 30.5+/-7.5 years). All patients were receiving corticosteroids at the time of the study. Variables evaluated were: disease duration, clinical pattern, disease activity (SLEDAI), cumulative damage index (SLICC/ACR), current and cumulative prednisone dose, duration of steroid treatment, and use of immunosuppressive agents. Osteoporosis was defined as a t score below 2.5 SD compared to a reference population of healthy women in at least one region of measurement.

Vertebral and femoral BMD were significantly lower in patients with SLE than in age matched controls. Osteoporosis was detected in 22.6% of patients. No significant differences in BMD were detected between patients according to clinical pattern or activity index, whereas patients with damage index > 0 (n = 46) had a significantly lower BMD at both the lumbar (p = 0.008) and the femoral (p = 0.05) level. Compared with non-osteoporotic patients with SLE, women with osteoporosis had similar age, lower body mass index, significantly longer disease duration (p < 0.0001), higher cumulative steroid intake (p < 0.006), and higher SLICC/ACR score (p < 0.01). Stepwise logistic regression analysis showed that disease duration is independently associated with osteoporosis (OR 1.2 for each year of disease, 95% CI 1.07-1.33). Since disease duration and duration of steroid treatment were highly correlated, a new stepwise logistic model was run without disease duration, which revealed that prednisone was associated with an increased risk for osteoporosis (OR 1.16 for each year of treatment, 95% CI 1.05-1.29).

Osteoporosis is a frequent feature in young patients with SLE. Disease duration is associated with an increased risk for osteoporosis, but the role of glucocorticoid treatment seems to be crucial. Steroid exposure was the only treatment related variable exerting an influence on the development of osteoporosis.