New ways to subclassify patients with myositis

• Autores: Ingrid E. Lundberg
• Localización: Journal of Internal Medicine, ISSN-e 1365-2796, Vol. 280, Nº. 1, 2016, págs. 4-7
• Idioma: inglés
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• Resumen

  • The idiopathic inflammatory myopathies (IIMs), collectively termed myositis, are a rare group of chronic disorders characterized by muscle weakness and low muscle endurance, predominantly affecting proximal muscle with, in typical cases, inflammatory infiltrates in skeletal muscles. The cell infiltrates in muscle tissue are mainly composed of T cells and macrophages, and together with the frequent presence of autoantibodies, they suggest that these are autoimmune diseases. Other organs are frequently involved in IIMs such as the skin, joints, lungs, gastrointestinal tract and heart, indicating that the IIMs are in many cases systemic inflammatory diseases. Patients with IIMs may present with muscle symptoms, skin rash, joint problems or pulmonary symptoms such as cough or dyspnoea. Thus, depending on their predominating clinical symptom and on local tradition, these patients are managed by different medical experts including rheumatologists, neurologists, internal medicine specialists, dermatologists or pulmonologists. Furthermore, IIMs may affect both children and adults, and some children develop a chronic disease that persists during adolescence into adulthood. Interdisciplinary team care is essential to support, to provide the best care for and to increase knowledge that will benefit patients with IIMs. Therapy for IIMs is based on pharmacological treatment in combination with physical exercise. The cornerstone of pharmacological treatment is high-dose glucocorticoids in combination with other immunosuppressive drugs, often with disappointing results, with many patients having persistent impairment of muscle function leading to difficulties in everyday life and low health-related quality of life. Therefore, there is an unmet need for new therapies. To meet this need, we must achieve a better understanding of the molecular mechanisms leading to muscle weakness and inflammation in the respective organs in these disorders. It has been a pleasure to see an increase in research activity in the field of IIMs over the past decade. Research into IIMs would benefit from a greater interdisciplinary approach. Multicentre studies across disciplines and continents are necessary for rare diseases like IIMs. To facilitate interdisciplinary research, we organized the First International Conference on Myositis in Stockholm in 2015. This conference was a great success with 150 investigators from 22 countries representing many disciplines meeting and sharing scientific ideas and experience from working in the IIM field.

    The IIMs are a heterogeneous group of disorders, probably with different pathogeneses in different subsets of patients. For many years, the IIMs have been subgrouped, based on differences in clinical and histopathological features, into polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM). Patients with IBM can be distinguished from those in the other two subgroups based on both clinical and histopathological features. Typical clinical features to support a diagnosis of IBM are early signs of finger flexor weakness and quadriceps weakness and muscle atrophy, as well as resistance to treatment with immunosuppressive drugs. Typical histopathological features include rimmed vacuoles and inclusions. These clinical and histopathological differences between IBM and PM/DM suggest that the predominant molecular mechanisms differ between IBM and the other two subsets. With regard to PM and DM, there are also clinical and histopathological differences, suggesting different molecular pathways between these two subsets. However, there are also shared features such as proximal muscle weakness, interstitial lung disease and autoantibody patterns, suggesting that some mechanisms may be shared between these subsets.