The Laboratory Test for the Diagnosis of Idiopathic Inflammatory Myopathies

Abstract

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of autoimmune muscle diseases with systemic involvement. Patients with IIM present with varying degrees of muscle disease, cutaneous manifestations, and internal organ involvement. The diagnosis of IIM is frequently delayed because of non-specific symptoms including weakness, easy fatigability, or myalgia. Laboratory tests can give clues for the diagnosis of myositis and other muscle diseases. Creatine kinase can be the screening tool for muscle diseases. About 40-60% of IIM had positive antinuclear antibody (ANA). Thus, positive ANA results increase the possibility of IIM diagnosis. In addition, the identification of myositis-related autoantibodies can help the diagnosis and classification. Myositis-specific autoantibodies (MSA) are found exclusively in IIMs and facilitate the identification of subsets of patients with relatively homogeneous clinical features. Myositis-associated antibodies are frequently found in association with other MSA; however, they may also be detected in various connective diseases.