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Brouwer et al studied a very large group of European patients with idiopathic inflammatory myopathies for myositis associated autoantibodies with a variety of methods.1 This is the largest group of patients with myositis ever studied for autoantibodies. The results substantially increase the existing knowledge about frequencies of autoantibodies in patients with inflammatory myopathies.
Compared with the pre-existing data, clinical associations of certain myositis-specific autoantibodies seem to be widening and are becoming less specific. Whereas the overwhelming majority of patients with anti-SRP up until now were reported to have polymyositis (PM),2 ,3 and anti-Mi-2 was almost completely specific for dermatomyositis (DM),3-5 Brouwer et al mention several anti-SRP positive DM and anti-Mi-2 positive PM cases, and even some patients with these autoantibodies and inclusion body myositis. The question is whether this is a matter of test or autoantibody specificity or a problem of adequate clinical diagnosis or classification as PM or DM. Moreover, the specificity of myositis related autoantibodies is further questioned by several violations of the well established rule that coincidences of myositis-specific antibodies are almost non-existent6—for example, by patients being positive for anti-Jo-1 and anti-Mi-2 or anti-SRP at the same time.
As the authors correctly state, the detection of more positive results is mostly due to the assay design, …