Clinical Usefulness of Autoantibodies in Idiopathic Inflammatory Myositis

One of the most important characteristics of systemic autoimmune diseases, including idiopathic inflammatory myopathies (IIM), is the immune response to self-antigens manifested by the production of autoantibodies that recognize a variety of cytoplasmic and nuclear antigens. In the last 40 years, autoantibodies of patients with IIM have been investigated; however, some of the fundamental questions related to these antibodies remain unresolved (1). Indirect immunofluorescence (IIF), in which HEp-2 cells are used as a substrate, is considered the gold standard for detecting antinuclear antibodies (ANA’s) in autoimmune rheumatic diseases. Using this method, specific antibodies that occur exclusively in these diseases were present in a great proportion of patients with myositis (50–80%) (2). It is important to note that patients with myositis more frequently have high titers of these antibodies than patients with overlap syndromes, and low titers usually are present in patients with myopathies associated with neoplasia. In contrast, these autoantibodies are usually absent in patients with inclusion body myositis, dystrophies, and other non-autoimmune myopathies. In general, even though the diagnostic value of these autoantibodies has been limited, they are useful as diagnostic markers since they closely correlate with certain clinical manifestations of disease and help identify clinical subgroups and to know about the prognosis of the IIM. Idiopathic inflammatorymyopathies has twomajor types of autoantibody groups: (1) those found primarily in patients suffering from polymyositis (PM) or dermatomyositis (DM) are known as myositis-specific autoantibodies (MSAs); these are not observed in other diseases of connective tissue and are almost completely absent in patients with muscular dystrophies and (2) those that appear in myositis overlap syndromes and in other connective tissue diseases, which correlate with certain clinical and/or pathophysiological conditions of myositis, are known as myositis-associated autoantibodies (MAAs) (3).