Background/Purpose: Systemic Lupus Erythematosus (SLE) is a systemic inflammatory disease which has an increased risk for comorbid osteoporosis, related to the disease and long term corticosteroid therapy. Bone turnover markers (BTMs) reflect the process of bone formation and resorption; imbalances in this process are associated with bone loss and osteoporosis. Changes in BTMs have been observed in SLE patients with conflicting results. This study examined the association between BTMs and their relationship to disease activity.

Methods: SLE patients were identified from a university research registry and biorepository of patients with rheumatic disease. Demographics, disease activity, medication use and laboratory data were collected. Serum was assayed for C-terminal telopeptide of type 1 collagen (CTX), a bone resorption marker, and osteocalcin (OC), a bone formation marker. Serum CTX index, expressed as a ratio of measured CTX value to upper limit of normal value for age and gender, was used for analysis. The patients were stratified by SLE disease activity index (SLEDAI): a score of <3 (low disease activity) and ≥3 (higher disease activity). We analyzed correlations between BTMs and variables that have known associations.

Results: Serum levels of BTMs were measured in 42 subjects of which 88% were white females with a median age of 36 years, and 19% had lupus nephritis or chronic kidney disease. Most were on ongoing corticosteroid treatment (68%) and 47% were on vitamin D supplementation. Only 36% had a serum vitamin D level >30 ng/mL and 32% were insufficient (20-30 ng/mL) and 32% were deficient (<20 ng/mL). The median OC value was 13.5 ng/mL (normal 9-42), and the median CTX index was 0.54. Subjects with a higher SLEDAI score had lower median OC level compared to those with low SLEDAI score (median [IQR] of 11 [10, 16] vs. 18 [13, 22], p=0.02). There were no significant differences in CTX between these two groups. There was a positive correlation between the CTX index and OC (r = 0.537, p<0.01).

Conclusion: SLE patients with higher disease activity had lower OC levels than in those with low disease activity, suggesting that inflammation may suppress bone formation. There was no difference in CTX index between patients with higher and low disease activity. Bone formation and resorption markers were positively correlated in our SLE cohort, suggesting a coupled bone turnover state. The next step is to determine if corticosteroid dosage plays a role in the decreased bone formation observed in this cohort.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/bone-turnover-markers-in-adults-with-systemic-lupus-erythematosus/