Reduced bone mineral density in patients with idiopathic inflammatory myopathies: a case-control study.

Background: Patients with idiopathic inflammatory myopathies (IIMs) are at risk of reduced bone mineral density (BMD).

Objectives: To compare the prevalence of reduced BMD between patients with IIMs and controls and to determine its risk factors.

Design: This was a single-center case-control study.

Methods: BMD was assessed by dual-energy X-ray absorptiometry. The prevalence of reduced BMD in IIM patients and age-and sex-matched non-rheumatological controls was compared. The BMD results of female IIM were also compared to age-matched female rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients. Independent factors associated with reduced BMD in IIM patients were identified by multivariate analyses.

Results: A total of 230 patients (IIM: 65, non-rheumatological controls: 65, RA: 50, SLE: 50) were recruited. The mean age of IIM patients was 58.6 ± 11.0 years and 76.9% were females. Significantly, more IIM patients had reduced BMD (73.8% versus 43.1%, p = 0.043) and osteoporosis (29.2% versus 13.8%, p = 0.033) than non-rheumatological controls. Multivariate analysis confirmed that IIM was independently associated with reduced BMD (OR: 2.12, p = 0.048, 95% CI: 1.01-4.46). The prevalence of reduced BMD was not significantly different between IIM, RA, and SLE patients but the mean hip BMD was the lowest in the IIM group (0.641 ± 0.152 g/cm²versus 0.663 ± 0.102g/cm² in the RA group versus 0.708 ± 0.132 g/cm² in the SLE group, p = 0.035). Lower body mass index and more advanced age were independently associated with lower BMD in IIM patients.

Conclusion: Reduced BMD was more prevalent in IIM patients than in non-rheumatological controls. Hip BMD was lower in patients with IIMs than RA or SLE. Close monitoring and early treatment are encouraged especially in patients with risk factors.