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

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

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

This was a single-center case-control study.

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.

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.

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.