Inflammatory myopathies. New concepts

Myopathies are diseases characterized by the primary affection of skeletal muscle. In general they present with muscle weakness, pain, contracture, paresthesias, rigidity, or fatigue. They can be hereditary, such as muscle dystrophies, congenital, myotonic, metabolic, and myasthenic, or acquired. Among the latter ones we include idiopathic inflammatory myopathies (IIM), toxic, endocrine, or infectious myopathies and myasthenia gravis. There is a current acceptance of considerable clinical and histopathological overlap among some muscle dystrophies and some IIM. However, the molecular profile is different and characteristic in each myopathy and the study into the patterns of expression of genes in the muscle can be useful in their differential diagnosis, including that of IIM.