Background/Purpose: Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disease characterized by recurrent flares. SLE patients are often treated with glucocorticoids, which place this population at risk of significant bone loss. Low bone mineral density (BMD) predisposes patients to fragility fractures, which may result in severe pain, disability and mortality.   The aims of this study are: 1) To determine the prevalence of low bone density and symptomatic fragility fractures in inception patients of the Toronto Lupus Cohort (TLC). 2) To determine the factors associated with low BMD in SLE inception patients.

Methods: Prospectively collected data from the TLC (1996-2015) of inception patients’ first BMD were analyzed. For pre-menopausal women/males <50 years, BMD ‘below expected range for age’ was defined by a Z-score ≤2.0 S.D.  For post-menopausal women/males age 50 or older, osteoporosis was defined by a T-score ≤-2.5 S.D and low bone mass by a T-score between -1.0 and -2.5 S.D. Patients’ BMDs were defined as abnormal if their Z-score was ≤-2.0 or T-score was <-1.0 S.D, and the remainder as normal. Descriptive analysis and logistic regression were employed to determine factors associated with abnormal BMD.

Results: Of 1807 patients in the TLC, 286 are inception patients with BMD results (mean age 37.9 years ± 13.7); 88.8% are female. The mean duration from SLE diagnosis to time of first BMD is 2.20 ± 2.57 years. The overall prevalence of abnormal BMD is 31.5%. In pre-menopausal women (n=173), the prevalence of BMD below expected range is 17.3%. In post-menopausal women (n=81), the prevalence of osteoporosis and low BMD are 12.3% and 43.2%, respectively. In males <50 years (n=22), the prevalence of BMD below expected range was 27.3%. In males age 50 or older, (n=10), the prevalence of osteoporosis and low BMD were 10% and 80%, respectively. In multivariate analysis, age at first BMD remained statistically significantly associated with abnormal BMD (44.72 ± 17.14 years), with an OR of 1.06 (p<0.0001). Cumulative dose of glucocorticoids up to the date of BMD was also significantly associated with abnormal BMD (11.55 grams/day ± 10.99), with an OR of 1.04 (p=0.009) (Table 1). Of 769 inception patients, 85 (11.1%) experienced symptomatic fragility fractures over the course of their disease.  

Conclusion: The prevalence of low BMD is high in SLE patients. Abnormal BMD is associated with older age and higher cumulative glucocorticoid dose. Identifying factors associated with low BMD is important in the development of preventative measures.  

*95% CI in parentheses                     **Up to time of first BMD                ***Immunosuppressives include: azathioprine, methotrexate, cyclophosphamide, mycophenolate mofetil, cyclosporine