Myositis is a group of acquired neuromuscular diseases associated with immune system dysfunction. Generally, the production of autoantibodies generally confirms the diagnosis. Among the myositis are inflammatory myopathies including polymyositis, dermatomyositis, inclusive myositis and a more recently described entity, autoimmune necrotizing myopathy. Unlike the former, histologically, autoimmune necrotizing myopathy is not inflammatory. It is often related to the use of statins, but not exclusively. The diagnostic criterion of autoimmune necrotizing myopathy usually resides in the positivity of autoantibodies to an enzyme, HMG-co-reductase (HMGCR).
In an article published in October 2016, an international consortium of nine countries described the results of anti-HMGCR assays in a population of 1906 people, the majority (1250) of whom had inflammatory myopathy. ELISA by immunoprecipitation of autoantibodies proved to be more sensitive and effective than the immunofluorescence method. Exposure to statins remains a major causative factor of autoimmune necrotizing myopathy. Simply stopping statin intake is usually not enough to stop the disease and immunosuppressive therapy is almost always necessary. Finally, the authors noted significant differences between countries, especially in Japan, where the anti-HMGCR rate was particularly low.
Anti-HMGCR antibodies as a biomarker for immune-mediated necrotizing myopathies: A history of statins and experience from a large international multi-center study. Musset L, Allenbach Y, Benveniste O, Boyer O, Bossuyt X, Bentow C, Phillips J, Mammen A, Van Damme P, Westhovens R, Ghirardello A, Doria A, Choi MY, Fritzler MJ, Schmeling H, Muro Y, García-De La Torre I, Ortiz-Villalvazo MA, Bizzaro N, Infantino M, Imbastaro T, Peng Q, Wang G, Vencovský J, Klein M, Krystufkova O, Franceschini F, Fredi M, Hue S, Belmondo T, Danko K, Mahler M. Autoimmun Rev., 2016 (Oct).