Patients with idiopathic inflammatory myopathies (IIMs) face several unmet needs which can prevent the attainment of optimal clinical outcomes. Each manuscript presented in this thesis addresses one such unmet need. In Chapter 4 (âPatient-centred standards of care for adults with myositisâ, accepted for publication at BMC Rheumatology), standards of care for adults with IIM are presented. The evidence base for therapy in IIM is limited, but these standards of care will support healthcare professionals and enable benchmarking of services against agreed optimum standards. In Chapter 5 (âThe EuroMyositis Registry: An international collaborative tool to facilitate myositis researchâ, published in Annals of Rheumatic Disease), pooled data regarding 3,067 cases from 11 countries are analysed. Several important new associations are described, including the strong influence of extramuscular involvement on disease severity in IIM. In Chapter 6 (âUsing serum troponins to screen for cardiac involvement and assess disease activity in the idiopathic inflammatory myopathiesâ, under peer review at Rheumatology) increased IIM disease activity in those with abnormal levels of cardiac troponin T (cTnT) or I (cTnI), including in those with a normal creatine kinase, is demonstrated. cTnI testing also appeared useful in screening for cardiac involvement. In Chapter 7 (âCytosolic 5â²-nucleotidase 1A autoantibody profile and clinical characteristics in inclusion body myositisâ, published in Annals of Rheumatic Disease) differences in mortality risk, clinical and histopathological features between anti-cytosolic 5â²-nucleotidase 1A autoantibody positive and negative inclusion body myositis patients are described. In Chapter 8 (âMuscle amyloid accumulation and disease activity in inclusion body myositis: A florbetapir positron emission tomography studyâ) positron emission tomography of muscle using a beta-amyloid tracer is presented. Significantly higher levels of muscle amyloid were identified in the inclusion body myositis group compared to a disease control group with polymyositis.