Evaluation of Bone Mineral Density, Hormones, Biochemical Markers of Bone Metabolism, and Osteoprotegerin Serum Levels in Patients with Ankylosing Spondylitis

HELMUT FRANCK, THOMAS MEURER, and LORENZ CHRISTIAN HOFBAUER

ABSTRACT.

Objective. To evaluate bone metabolism in patients with ankylosing spondylitis (AS) and test the hypothesis that osteoprotegerin (OPG) serum concentrations are correlated with the severity of bone loss as assessed by bone mineral density (BMD) and biochemical markers of bone turnover. Osteoporosis occurs frequently in patients with AS and OPG represents a soluble decoy receptor that neutralizes receptor activator of nuclear factor-kB ligand (RANKL), an essential cytokine for osteoclast function.

Methods. Clinical data, radiographs of the spine, BMD of lumbar spine and the femur, biochemical markers of bone turnover, and serum levels of OPG were evaluated in 264 patients with AS (72% men) and 240 age-matched healthy controls (76% men).

Results. OPG serum levels were significantly lower in patients with AS compared to controls (1.84 ± 1.15 vs 3.54 ± 2.18 pmol/l, p < 0.001), and in contrast to controls, were not positively correlated with age. In addition, BMD of the hip and the femoral neck were significantly lower in patients with AS than in controls. There were positive correlations in patients with AS between BMD of the femoral neck and free testosterone serum levels in men and free estradiol serum levels in women, respectively. Patients with AS and osteoporosis had higher biochemical markers of bone resorption and inflammatory activity.

Conclusion. Bone loss in patients with AS is associated with low sex steroid hormone serum levels, high biochemical markers of bone resorption and inflammatory activity, low OPG serum levels, and lack of compensatory age-related increase of OPG serum levels. (J Rheumatol 2004;31:2236-41)

Key Indexing Terms:

OSTEOPROTEGERIN
ANKYLOSING SPONDYLITIS
OSTEOPOROSIS

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From the Center of Rheumatology, Oberammergau and the Department of Gastroenterology, Endocrinology and Metabolism, Philipps-University, Marburg, Germany.

Supported by grants Ho 1875/3-1 (Heisenberg program) and Ho 1875/5-1 from the Deutsche Forschungsgemeinschaft to Dr. Hofbauer.

H. Franck, MD, Physician-in-Chief; T. Meurer, MD, Fellow in Rheumatology, Center of Rheumatology; L.C. Hofbauer, MD, Fellow in Endocrinology, Department of Gastroenterology, Endocrinology and Metabolism, Philipps-University.

Address reprints requests to Dr. H. Franck, Rheumatologie, Eyrlgasse 5, D-82487 Oberammergau, Germany.

Submitted November 24, 2003; revision accepted May 20, 2004.

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