Diagnosis of dermatomyositis: Autoantibody profile and muscle pathology

Dermatomyositis (DM) is an idiopathic inflammatory myopathy, which not only affects skeletal muscle and skin, but it is also associated with arthritis/arthralgia, interstitial lung disease and cancer. The diagnostic criteria for myositis that Bohan and Peter formulated in 1975, which are often still used now, depend on the presence of a characteristic skin rash for classification of DM; without it, a diagnosis of polymyositis is given. However, advances in understanding the etiology of idiopathic inflammatory myopathies over the past few decades are impressive, encompassing discovery of myositis-specific/associated autoantibodies and development of muscle pathology, and enable us to classify them more precisely based on the underlying etiology. Correlations between clinical phenotypes and DM-specific autoantibodies (anti-Mi-2, TIF-1, NXP2, MDA5 and SAE) have been mostly elucidated, suggesting the diagnostic utility of autoantibody measurement. Advances in muscle pathology include analysis at the molecular level, such as the detection of myxovirus resistance protein A in myofibers, which can be used as a sensitive and specific pathological marker of DM. Today, a multidisciplinary approach – autoantibody profiling and pathological assessment, as well as clinical evaluation – is cardinal for a diagnosis of DM. The present review consolidates current knowledge about autoantibodies and muscle pathology in terms of diagnostic practice of DM.