Amyopathic dermatomyositis – a ‘feel‐good’ dermatology story

Abstract

In this issue of the BJD, Concha and colleagues review the history surrounding the recognition and characterization of amyopathic dermatomyositis (ADM), detail its clinical and serological features, and assess updated criteria concerning its diagnosis in affected patients. This is a story that dermatologists should be proud to read, as it underscores the critical role our specialty plays in advancing understanding of dermatomyositis (DM) specifically and connective tissue diseases more generally. Although largely ignored for decades by other specialists who treat DM, recognizing ADM as a DM subtype and developing accurate diagnostic criteria is important for appropriately evaluating and treating affected patients, as they traditionally have often been misdiagnosed as having cutaneous lupus erythematosus (CLE) in the face of underlying malignancy and interstitial lung disease risk similar to patients with classic DM who manifest myositis. The Bohan and Peter idiopathic myositis (IIM) classification criteria has represented the major IIM classification criteria since 1975. Indeed, although Bohan and Peter recognized cutaneous disease occurs in DM, their criteria demand muscle disease be present in order to make a DM diagnosis. The story of ADM begins with a report by the dermatologist, Lawrence Krain, who observed six patients with cutaneous DM features who initially lacked muscle weakness. Krain stressed the importance of recognizing DM in the absence of muscle weakness, and delayed diagnosis may have had a negative impact on at least two of his patients who had associated pulmonary disease. The term ‘ADM’ was then coined in 1979 by the rheumatologist, Carl Pearson, but it received little further attention until Euwer and Sontheimer described six patients with ADM in 1991 and proposed diagnostic criteria. Despite additional work solidifying evidence of ADM as a DM subtype in ensuing years, updated IIM criteria proposals by numerous authors who recognized a need to update the Bohan and Peter criteria failed to recognize it. The culmination of this work is acceptance of ADM as a true DM subtype in IIM criteria developed in 2004, and most importantly in the recently validated 2017 European League Against Rheumatism/American College of Rheumatology (EULAR/ ACR) classification criteria for IIMs. Concha and colleagues also detail clinical features of ADM to aide dermatologists in their evaluation of patients suspected of having it, including cutaneous features, histological findings in skin biopsies, significance of myositis-associated or -specific autoantibodies, and clues to its distinction from CLE. The perseverance of dermatologist clinician/researchers such as Sontheimer and Werth in working towards acceptance of ADM as a DM subtype hopefully will serve as motivating factors for dermatologists interested in DM into the future. More work certainly deserves and needs to be done, as recent work by Werth, the senior author of this BJD manuscript, has shown up to 26% of patients with ADM still fail to meet diagnostic criteria set forth in the 2017 EULAR/ACR IIM classification. Thus, improvement of these diagnostic criteria, as well as work to identify specific features that may be able to distinguish ADM from CLE accurately, are still needed.