Relation of the Serum Levels of DKK-1 and Osteoprotegerin with Bone Mass in Tightly Controlled Rheumatoid Arthritis

To analyze the association between serum levels of osteoprotegerin (OPG) and Dickkopf-related protein 1 (DKK-1) and the annual percent change (Δ%) in bone mineral density (BMD) in patients with tightly controlled rheumatoid arthritis (RA).

Observational mixed-study. RA patients followed-up with a tight-control strategy were included. Bone densitometries were performed at baseline (T0) and follow-up (T1) and serum levels of OPG and DKK-1 were measured by ELISA also in T0 and T1; additional clinical variables included disease activity measures, and treatment for RA and osteoporosis. Descriptive bivariate and multivariate analyses, stratified by gender, were performed.

We included 97 RA patients (70% female, with a mean age of 53 years, and 76% with low activity by DAS28); 95% were treated with DMARDs and 37% with anti-osteoporotic drugs. Mean time between T0 and T1 was 2.7 years. Most patients had their BMD improved. The mean Δ%BMD was +0.42% for lumbar spine, +0.15% for femoral neck and +0.91% for total femur. In men, baseline OPG was significantly associated with higher BMD loss (β coefficient -0.64) at the femoral neck. In women, DKK-1 was associated with higher BMD loss at the femoral neck (β coefficient -0.09), and total femur (β coefficient -0.11); however, DKK-1 was associated with lower BMD loss at the lumbar spine (β coefficient 0.06).

In tightly controlled RA patients, we have found no evidence of bone loss. The role of DKK1 and OPG seems small and might be related to sex and location.