The idiopathic inflammatory myopathies (IIM) are a heterogeneous group of disorders characterized by muscle weakness, resulting from chronic muscle inflammation of unknown cause. Patients with IIM have a variety of autoantibodies with various clinical utilities that fall into two main groups.
The first group is found only in patients with myositis and is known as Myositis Specific Autoantibodies (MSA). The MSAs have been shown to be highly specific for patients with polymyositis (PM), dermatomyositis (DM), anti-synthetase syndrome, necrotizing myositis and overlap syndromes.
The second group of antibodies is considered Myositis Associated Autoantibodies (MAA) and can be found in patients with overlap syndromes such as polymyositis/scleroderma. MAA can also be found in non-overlap syndromes.