Uncoupling of bone metabolism in rheumatoid arthritis patients with or without joint destruction: assessment with serum type I collagen breakdown products.

In this study we investigate bone metabolism in patients with rheumatoid arthritis (RA), with or without joint destruction, using serum biochemical markers of bone turnover. Three hundred eighteen patients (disease duration >2 years; mean 9 years) were divided into those with joint destruction, that is, with Larsen wrist X-ray index > or =2 (n = 173) and those without joint destruction, that is, with Larsen wrist X-ray index <2 (n = 145). Bone formation was assessed by serum osteocalcin levels and bone resorption by a new assay for serum type I collagen C-telopeptide breakdown products (serum CTX). Osteocalcin levels were significantly lower in both destructive (-17%) and nondestructive (-22%) groups compared with 319 healthy gender- and age-matched control subjects (p < 0.001 for both groups), but were similar in the two arthritis groups. CTX levels were increased in patients with destructive arthritis compared with controls (+35%, p < 0.001), but were not different between those with nondestructive arthritis and controls. In patients with joint destruction, decreased bone formation rate was amplified in those on steroids (n = 72) compared with nonusers (n = 101) as demonstrated by lower osteocalcin levels (p = 0.02). CTX levels, but not osteocalcin levels, were positively correlated with indices of disease activity and, moreover, of joint destruction (p < 0.002-0.0001). These results indicate that bone metabolism is uncoupled in patients with RA. Bone formation appears to be reduced both in patients with and without joint destruction, whereas resorption is increased only in patients with joint destruction in relation to disease activity.