OBJECTIVES: This real-world, retrospective study compared baseline demographics, clinical characteristics, comorbidities, treatment, and incidence rates (IRs) of disease outcomes in patients with dermatomyositis (DM), polymyositis (PM) and matched controls (MCs).

METHODS: De-identified clinical data were extracted from the US Optum^® electronic health records (EHR) database. During the study period (1 April 2016-31 March 2021), patients with incident DM (n=4275) and PM (n=4559) were assessed for baseline treatment, demographic, and clinical characteristics. IRs (per 100 person years) of 13 adverse events (AEs) were estimated during follow-up. IRs were also estimated in an equal number of sex- and age-MCs without idiopathic inflammatory myopathies.

RESULTS: Mean (standard deviation) age at baseline was 54.46 (15.49) years in the DM and 57.31 (15.46) years in the PM cohort, with higher prevalence in females than males in both cohorts. At baseline, Raynaud’s phenomenon was the most prevalent clinical characteristic in both cohorts (DM=8.58%; PM=7.92%). Hypertension (DM=50.34%; PM=63.92%), hyperlipidemia (DM=40.26%; PM=51.26%), and gastroesophageal reflux disease (GERD) (DM=31.13%; PM=34.55%) were the most prevalent comorbidities. Systemic steroids were the most commonly prescribed medication (DM=70.29%; PM=68.33%). IRs of all AEs were higher in patients than MCs. Specific IRs were: GERD (DM=10.32, MCs=6.41; PM=12.82, MCs=6.43); cardiac dysrythmia (DM=5.73, MCs=3.65; PM=7.97, MCs=4.33); ischemic heart disease (DM=3.95, MCs=2.28; PM=5.70, MCs=3.07); dysphagia (DM=5.33, MCs=2.03; PM=5.28, MCs=1.87); heart failure (DM=2.80, MCs=1.55; PM=4.24, MCs=2.03); interstitial lung disease (DM=2.75, MCs=0.48; PM=2.38, MCs=0.49); malignancy excluding non-melanoma skin cancer (DM=2.46, MCs=1.65; PM=2.35, MCs=1.84); death (DM=2.20, MCs=0.76; PM=2.35, MCs=1.84); and cardiomyopathy (DM=1.21, MCs=0.74; PM=2.03, MCs=0.79).

CONCLUSIONS: In incident DM and PM patients, Raynaud’s phenomenon was the most prevalent baseline clinical characteristic (although <10% prevalence), systemic steroids were the modal baseline treatment, and GERD, cardiac dysrhythmia, and ischemic heart disease had the highest IRs. DM and PM patients had higher IRs than MCs for all outcomes.