Clinical heterogeneities and prognoses of patients with myositis specific antibody negative dermatomyositis: a retrospective study in China

Objective The clinical features of myositis specific antibody negative dermatomyositis (MSA negative DM) varied greatly, and there were few reports in the literatures. This study aimed to describe and expand the clinical phenotypes and prognoses of MSA negative DM patients. Methods MSA negative DM patients were identified from January 2010 to June 2020. We retrospectively reviewed the clinical features and laboratory data. The survival status was followed up until July 31. 2020 SPSS version 21.0 and R version 3.6.1 software were used for the statistical analyses. Results A total of 97 MSA negative DM patients were enrolled. The most common type of rashes was heliotrope rash (80.4%). More than half of the patients (55.7%) had interstitial lung disease (ILD), and seven of them developed rapid progressive ILD. There were eleven patients with tumours. During the follow-up, twelve patients died, of whom 5 (41.7%) died due to infection. Two phenotypes of MSA negative DM patients were identified by cluster analysis. Patients in cluster 1 developed muscle weakness, mechanic’s hands, arthritis, and ILD more frequently. Patients in cluster 2 had a higher incidence of heliotrope rashes. Patients in cluster 1 tended to have worse prognoses, wherein the 1-year and 5-year survival rates (81.1% and 78.4%, respectively) were lower than those in cluster 2 (97.6% and 95.2%, respectively), with p-value 0.04 and 0.056, respectively. Conclusion Through cluster analysis, different clinical phenotypes of MSA negative DM patients were determined. The prognoses of the two subgroups were different in terms of survival rate and cause of death.