The diagnosis and classification of amyopathic dermatomyositis: a historical review and assessment of existing criteria

Background Diagnostic criteria are used to identify a patient having a disease in a clinical setting, whereas classification criteria create a well-defined population for research purposes. The diagnosis and classification of amyopathic dermatomyositis (ADM) have not been recognized by most existing criteria for idiopathic inflammatory myopathies (IIMs). To address this, several criteria were proposed to define ADM either as a distinct disease entity or as a subset of the spectrum of IIMs. Objectives To discuss the diagnosis and classification of ADM and to assesses the available criteria in identifying cases of ADM and/or distinguishing it from dermatological mimickers such as lupus erythematosus. Methods We conducted an extensive literature search using the PubMed database from June 2016 to August 2018, using the search terms 'amyopathic dermatomyositis', 'diagnosis' and 'classification'. Results The European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) criteria, which are the only validated classification criteria for adult and juvenile IIM and their major subgroups, include three cutaneous items (Gottron sign, Gottron papules, heliotrope rash) to be able to classify ADM. This international and multispecialty effort is a huge step forward in the classification of skin-predominant disease in dermatomyositis. However, about 25% of the population with ADM do not meet two out of the three skin features and are misdiagnosed or classified as having a different disease entity, most commonly lupus erythematosus. Conclusions These gaps rationalize the continuous assessment and improvement of existing criteria and/or the development of validated, separate and skin-focused criteria for DM.