The idiopathic inflammatory myopathies, collectively named myositis, can be subclassified into polymyositis, dermatomyositis and inclusion body myositis. Patients with polymyositis and dermatomyositis usually respond to immunosuppressive treatment, at least with partial improvement, whereas patients with inclusion body myositis often are treatment resistant. These differences in treatment response suggest different pathogenic mechanisms and that treatment strategies should be different in these different subsets of myositis. Only a few controlled trials have been performed in patients with myositis, thus treatment recommendations are mainly based on case series and clinical experience. This lecture will include update on (1) Pharmacological and non-pharmacological treatment (exercise) for polymyositis and dermatomyositis; (2) The role of biologics in myositis (2) Outcome measures for polymyositis and dermatomyositis, and (3) Treatment recommendations for inclusion body myositis.
For polymyositis and dermatomyositis there is scientific data to support that treatment should be based on a combination of immunosuppressive treatment and physical exercise. The basis of treatment is still glucocorticoids often with high starting doses e.g. 0.75- 1 mg/kg/day needed. Improvement of muscle performance is often slow and high doses of glucocorticoids may be needed for 1 month of more. As side effects of glucocorticoids are common and some patients may not respond favorably to glucocorticoid treatment alone, most experts suggest another immunosuppressive agent as glucocorticoid saving and to improve the effects of treatment. The most often used drugs are methotrexate and azathioprine. So far the experience of biologics in treatment of polymyositis and dermatomyositis is limited but the results of a placebo-controlled trial using rituximab will be discussed. Physical exercise in combination with immunosuppressive drugs has clear beneficial effects in established disease on muscle performance and health related quality of life and should be recommended. Furthermore, physical exercise seems to be safe also in early phases of disease.
The most important outcome measure in polymyositis and dermatomyositis is muscle performance, strength and endurance, and the influence of disease activity or damage respectively on these measures. In addition, both polymyositis and dermatomyositis, are systemic inflammatory diseases and other organs are frequently involved and therefore also need to be measured. The variability of disease manifestations of polymyositis and dermatomyositis is captured using the International Myositis Assessment and Clinical Studies Group (IMACS) core set of disease activity.
Inclusion body myositis (IBM) is a slowly progressive disorder, where the importance of the immune system in the pathophysiology is unclear. Some patients experience a partial improvement with glucocorticoids in the initial phases of disease whereas other patients do not respond at al. therefore IBM is an important differential diagnosis to refractory polymyositis. Characteristics of IBM will be discussed as well as results of some pharmacological interventions.
Disclosure of Interest None Declared