[Laboratory abnormalities and autoantibodies]

Laboratory tests in inflammatory myopathies (IIM) are of great help in the diagnosis of these diseases. Two main groups can be defined, one of them quantifies the muscle enzymes that reflect muscle inflammation and the other one detects the presence of autoantibodies which reflect the autoimmune process in these diseases. The most important muscle enzyme is creatine kinase and other enzymes to take into consideration are aspartate and alanine aminotransferase, aldolase and lactic dehydrogenase. In the autoantibodies group, antinuclear antibodies are the most important, since they occur in approximately 50-80% of patients with IIM and help define the distinct disease sub-groups. They are divided into myositis specific antibodies (MSA) and myositis associated antibodies (MAA). The most important MSA are anti-Jo-1 antibody which occur in patients with Polymyositis and anti-Mi-2 antibody that occur in patients with Dermatomyositis.