Bone mineral density and frequency of osteoporosis in female patients with rheumatoid arthritis: Results from 394 patients in the Oslo County rheumatoid arthritis register

OBJECTIVE: To examine the bone mineral density (BMD), frequency of osteoporosis, and risk factors for BMD reduction in a representative population of female rheumatoid arthritis (RA) patients ages 20-70 years. METHODS: BMD in the femoral neck, total hip, and spine L2-4 (anterior-posterior view) was measured in 394 RA patients recruited from a validated county RA register (completeness 85%) comprising 721 women ages 20-70 years. BMD was measured with dual-energy x-ray absorptiometry, and age-specific values were compared with pooled values from a European/US population of healthy subjects free from earlier fractures, chronic diseases, and medications influencing bone metabolism. A multiple linear regression model was used to determine individual predictors of BMD. RESULTS: No statistically significant differences were found in demographic, disease activity, disease severity, or health status parameters between the RA register patients in whom BMD was measured and the remaining register patients. Femoral neck BMD was significantly reduced by 4.2% in the age group 50-59 years, and by 5.0% in those ages 60-70 years. For BMD in the total hip, the significant reductions were 3.7%, 6.0%, and 8.5% in the age groups 40-49 years, 50-59 years, and 60-70 years, respectively. No significant reduction in spine L2-4 BMD was found. A 2-fold increased frequency of osteoporosis was observed in all 4 age groups of RA patients compared with the reference population, ranging from 0% to 28.6% in the femoral neck, 0% to 29.9% in the total hip, and 1.8% to 31.5% in the spine. Predictors of reduced BMD were as follows: at the femoral neck, older age, low body weight, current use of corticosteroids, greater physical disability (as measured by the modified Health Assessment Questionnaire M-HAQ), and presence of rheumatoid factor; at the total hip, older age, low weight, current use of corticosteroids, and higher M-HAQ disability score; and at the lumbar spine, older age, low weight, and current use of corticosteroids. CONCLUSION: Register-based prevalence data on BMD reduction in female RA patients ages 20-70 years are presented for the first time in this report, which demonstrates a 2-fold increase in osteoporosis in this representative population.