The histological findings in muscle biopsies of inflammatory myopathies have been divided into 2 groups: A) Endomisial infiltrates mainly by T CD8+, CD4+ and macrophages and B) Perivascular infiltrates by CD4+, B cells and macrophages. The first kind of infiltrate suggests an immune reaction against muscle fibers very common in PM and inclusion body myositis, On the other hand the perivascular infiltrate is a hallmark of DM. It has ben shown that autoantigens related with myopathies such as Mi-2, Jo-1, OJ, PL12, Ku, PM/Scl are able to suffer proteolytic cleavage by granzyme B and other stimulus induced by cytotoxic T cells. In this chapter we will review the histological and molecular findings of inflammatory myopathies but we will also discuss a special group of myopathies related to the presence of antibodies against the SRP complex, in particular the SRP72 and SRP54 antibodies, which are associated with a poor prognosis and clinical outcome and present an inadequate response to conventional treatment. � 2009 Elsevier Espa�a, S.L
