AB0616 REDUCED BONE MINERAL DENSITY IN PATIENTS WITH IDIOPATHIC INFLAMMATORY MYOPATHIES: A LONGITUDINAL STUDY

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Background:Reduced bone mineral density (BMD) leads to fragility fracture which is associated with a significant morbidity and excess mortality [1,2]. Patients with idiopathic inflammatory myopathies (IIM) should be at a heightened risk of reduced BMD as a result of the systemic inflammation, reduced mobility and corticosteroid use [3]. A previous cross-sectional study demonstrated a high prevalence of osteoporosis (23.7%) and osteopenia (47.4%) in a cohort of IIM patients [4]. However, longitudinal data are lacking.Objectives:To assess the BMD of IIM patients longitudinally and to investigate the factors associated with accelerated bone loss.Methods:This is a single centered observational study. Existing adult Chinese patients with IIMs who had serial BMD measurements done were recruited. The diagnosis of IIMs was based on the Bohan and Peter’s criteria with definite or probable cases being included [5]. Patients with clinically amyopathic disease must have the typical Gottron’s papules or heliotrope rash as determined by rheumatologists or dermatologists, and with no symptoms or signs of muscle involvement according to Sontheimer [6]. BMD was measured by dual energy X-ray absorptiometry (DEXA). Clinical variables thought to be associated with bone health were documented.Results:All together 28 patients were studied. The mean age of the patients at disease onset was 46.1 years (S.D. 12.2). There was a female predominance (92.9%). The subgroups of IIMs were: dermatomyositis (39.3%), polymyositis (25.3%), clinically amyopathic dermatomyositis (21.4%) and immune mediated necrotising myopathy (14.3%). Only a minority of the patients smoked (7.1%) and none of them drinks regularly. About one fifth of the patients were underweight. All patients have been exposed to systemic corticosteroid, while 82.1% of them were still on it between the two scans with 32.1% even on high dose (>0.5mg prednisolone/kg/day). Three out of the 28 patients (10.7%) was found to be osteoporotic at baseline and 17 patients (60.7%) were osteopenic. Follow-up DEXAs were performed mostly 5 to 10 years after the initial scan. Despite 8 patients (28.6%) were given active anti-osteoporotic medications, the bone health deteriorated significantly. The mean baseline neck of femor BMD dropped from 0.711 to 0.657 g/cm2 (p=0.042) on follow-up, while the total lumbar BMD from 0.951 to 0.905 g/cm2 (p=0.036). The T-score in 11 patients (39.3) reached osteoporotic range at the second DEXA. Together with the patients with osteopenia, 78.6% of the IMM patients had reduced BMD at the follow-up scan. Actually, 5 patients (17.9%) already had one episode of fragility fracture. The use of high dose corticosteroid in between the 2 scans was found to be associated with a greater degree of mean BMD loss in the hip (-0.171 vs -0.007 g/cm2, p=0.007).Conclusion:Reduced BMD is prevalent in patients with IIM. Follow-up study revealed significant worsening of bone health. High dose corticosteroid use might be especially detrimental. Liberal assessment of BMD and use of anti-osteoporotic drugs in IIM patients are advisable. Prompt use of steroid-sparing agents to minimize steroid exposure may also be helpful.