LAUSR

Background Patients with polymyositis and dermatomyositis (PM/DM) are characterized by chronic muscle weakness due to autoimmune-mediated myositis and are usually treated with corticosteroids initially. PM/DM patients prone to develop osteoporosis and subsequent fractures but are rarely investigated. Objectives To explore the incidence rate (IR) and risk factors of osteoporotic fractures (OFs) among adult PM/DM patients. Methods We conducted a cohort study by utilizing the Taiwan National Health Insurance database. PM/DM patients and respective age- and gender-matched cohort without PM/DM were enrolled. The primary endpoint was the initial event of OFs. We used the Cox proportional hazard model to study the risk factors of OFs in the PM/DM cohort. Results Among 2391 PM/DM patients (67.8% female, mean age: 49.5 years) followed for a mean (SD) of 6.1 (5.0) years, 116 developed vertebral fractures, 32 had hip fractures, and 14 experienced radius fractures (IR: 8.18, 2.20, and 0.96 per 1000 person-years, respectively, Table 1). Compared with the matched cohort, the PM/DM patients had higher IR ratios (IRRs) (95% CIs) of OFs at all age groups at enrollment: 3.27 (2.19 to 4.81, p<0.0001) for people <50 years and 2.29 (1.85 to 2.82, p<0.0001) for those ≥50 years. The IRRs were 2.39 (1.92 to 2.94, p<0.0001) for vertebral fractures and 1.62 (1.07 to 2.38, p=0.0093) for hip fractures. PM/DM patients experienced vertebral fractures and hip fractures at younger ages (62.2 vs 68.4 and 66.0 vs 75.4 years, respectively; both p<0.001). Multivariable Cox regression analyses showed that being female gender, age ≥50 years, having hypertension, coronary artery disease, asthma, and using daily prednisolone equivalent to >5 mg are associated with OFs.Table 1. IRs and IRRs of osteoporotic fractures: overall and subgroup analysis Subgroup IM IR Control IR IRR (95% CI) p Value Overall fracture 10.90 5.23 2.08 (1.73 to 2.49) <0.0001  Age <50 year 4.51 1.38 3.27 (2.19 to 4.81) <0.0001  Age ≥50 year 22.59 9.85 2.29 (1.85 to 2.82) <0.0001 Vertebral fracture 8.18 3.43 2.39 (1.92 to 2.94) <0.0001  Age <50 year 3.39 0.98 3.47 (2.17 to 5.44) <0.0001  Age ≥50 year 16.82 6.33 2.66 (2.07 to 3.39) <0.0001 Hip fracture 2.20 1.36 1.62 (1.07 to 2.38) 0.0093  Age <50 year 0.65 0.10 6.56 (1.75 to 24.6) 0.0027  Age ≥50 year 4.87 2.83 1.72 (1.09 to 2.62) 0.0081 Radius fracture 0.96 0.83 1.15 (0.60 to 2.02) 0.3081  Age <50 year 0.43 0.35 1.25 (0.31 to 3.69) 0.3289  Age ≥50 year 1.86 1.40 1.35 (0.62 to 2.63) 0.1857 IR, incidence rate per 1000 person-year; IRR, incidence rate ratio; CI, confidence interval. Conclusions Adult PM/DM patients had a high IR of vertebral and hip fractures. Patients who were female, advanced age, having certain comorbidities, and exposed to corticosteroid exhibited a higher risk. Disclosure of Interest None declared