23 Detecting cardiac involvement in the idiopathic inflammatory myopathies using cardiovascular magnetic resonance

Background Idiopathic inflammatory myopathies (IIM) are multi-system diseases characterised by inflammation of skeletal muscle.1 Cardiac involvement is associated with worse clinical outcomes2 however detecting cardiac disease is challenging as traditional imaging modalities lack sensitivity and specificity. Serum troponin T (TnT) assessment is also limited as it is leaked from skeletal muscle, which is often abnormal in this disease.3 In this study, we use CMR to look for cardiac involvement and compare it to both troponin T and troponin I (TnI) measurement. Methods Patients with a new diagnosis of IIM, or a flare of existing disease, were recruited. They underwent CMR including parametric mapping, late gadolinium enhancement (LGE) and blood biomarker assessment including TnT and TnI. The data was compared to a heathy control group of 25 participants. Results 59 patients underwent CMR (median age 54 years, IQR 42–64, 68% female). Mean left ventricular (LV) systolic function in patients was normal (LVEF 60%±9%) and was no different to healthy controls (LVEF 61%±4%, P=0.72). LV dysfunction was seen in 9/59 (15%) patients. IIM patients showed significantly elevated mean native T1 (1045±39 vs 995±21 ms, p+) and 26/59 (44%) patients had negative TnI (TnI-). Mean LV systolic function in TnI+patients was normal (LVEF 60%±8%) and was no different to TnI-patients (LVEF 61%±11%, P=0.77). TnI+patients showed elevated native T1 (1055±39 vs 1032±35 ms, p=0.019) and elevated myocardial T2 (52.3±6.5 vs 48.8±6.5 ms, p=0.012) values compared to TnI-patients (figure 2). Even though TnI-patients had a lower T2 value, it was still in the mildly abnormal range (48.8 ms). Conclusion Myocardial abnormalities in IIM can be detected using CMR parametric mapping and LGE techniques. TnT is not a good marker for this, with TnI correlating better however still missing 36% of cases which CMR would suggest have mild active myocardial disease. References Schmidt J. Current classification and management of inflammatory myopathies. J Neuromuscul Dis. 2018;5(2):109–129. doi:10.3233/JND-180308. Schwartz T, Diederichsen LP, Lundberg IE, Sjaastad I, Sanner H. Cardiac involvement in adult and juvenile idiopathic inflammatory myopathies. RMD Open. 2016;2(2):e000291. doi:10.1136/rmdopen-2016–000291. Aggarwal R, Lebiedz-Odrobina D, Sinha A, Manadan A, Case JP. Serum cardiac troponin T, but not troponin I, is elevated in idiopathic inflammatory myopathies. J Rheumatol. 2009 Dec;36(12):2711–4. doi: 10.3899/jrheum.090562. Epub 2009 Oct 15. PMID: 19833747.