Inflammation of a muscle, especially a voluntary muscle, characterized by pain, tenderness, and sometimes spasm in the affected area.
Causes of myositis include infection, trauma, and infestation by parasites.

    

Inflamatory myopathies are a group of muscle diseases involving the inflimation and degeneration of skeletal muscle tissues. They are thought to be autoimmune disorders. These include dermatomyositis, polymyositis and inclusion body myositis. Although all of these diseases result in muscle weakness, each is unique in its own development and treatment.