This paper reviews the knowledge we continue to gain in the areas of pathogenesis, evaluation of disease activity, and interventional strategies with regards to idiopathic inflammatory myositis. Potential new diagnostic criteria incorporate the use of magnetic resonance imaging and other imaging modalities along with the use of muscle biopsy pathologic features including that of immunologic markers. Specifically, this criterion reflects the upregulation of major histocompatibility complex molecules on muscle tissue during acute inflammation.