Idiopathic inflammatory myopathies: diagnosis, treatment and outcome

The idiopathic inflammatory myopathies (IIM) in adults are a heterogenic group of disorders characterized by muscle inflammation and progressive muscle weakness. This group consists of five subacute-onset disorders: polymyositis (PM) which is extremely rare, (clinically amyopathic) dermatomyositis (DM), nonspecific or overlap myositis (NSM), necrotizing autoimmune myopathy (NAM), and sporadic inclusion body myositis (IBM). The investigations described in this thesis focus on diagnosis, treatment and outcome in adult patients with idiopathic inflammatory myopathies. Chapter 2 describes the diagnostic value of the combination of MRI of the skeletal muscles and muscle biopsy in patients suspected of having a (sub)acute IIM. In chapter 3 we assessed the disease course in patients with endomysial inflammation with invasion of non-necrotic muscle fibers in the muscle biopsy, hypothesizing that these patients show a disease course consistent with IBM. In chapter 4 the quality of case reports of 92 publications describing 915 patients with myositis was assessed. In chapter 5 the results of the Dexa Myositis Trial are presented. In this RCT monthly pulsed oral dexamethasone was compared with daily oral prednisolone in 62 newly diagnosed patients. In Chapter 6 we evaluated the disease course in myositis. In Chapter 7 we report three patients with a proven subacute myositis who recovered spontaneously. A general discussion of our findings is presented in chapter 8.