The importance of including amyopathic dermatomyositis in the idiopathic inflammatory myositis spectrum

The objective of this review is to summarise the published evidence that supports the existence of amyopathic dermatomyositis (ADM) and its clinical significance including risk for rapidly progressive, fatal interstitial lung disease (ILD) and possible risk for internal malignancy. By establishing such inherent risks, we hope to establish the importance of formally recognising ADM as a subset of dermatomyositis (DM). Population-based epidemiologic studies have suggested that amyopathic DM might account for 20% of the total population of dermatomyositis (DM) patients (1). Patients presenting with ADM have been reported by investigators of multiple nationalities to be at risk for rapidly progressive, potentially fatal ILD (2-5). In addition, a new autoantibody, anti-CADM-140, has been reported to be a risk factor for the development of interstitial lung disease in CADM patients (6-9). It has been argued that ADM patients may be at increased risk of developing internal malignancy compared to the general population, though its rate in comparison to classic DM (CDM) needs further study (1, 10-12). In our population, 41% of CADM patients were previously classified as LE or UCTD. We conclude that ADM is a real entity that makes up a significant portion of the DM disease. It is important to formally recognise amyopathic DM as a subset of DM as it carries increased risk of ILD and possibly malignancy. Without appropriate disease classification, the opportunity for ILD and malignancy screening may be missed.