Increased rates of idiopathic inflammatory myopathies during the COVID-19 pandemic: a single-centre experience.

Objectives: Higher-level evidence is required to discern whether the incidence of idiopathic inflammatory myopathies (IIM) has increased during the COVID-19 pandemic and whether the disease pattern and course have changed. We aimed to analyse patients who were diagnosed with IIM at our tertiary care centre during the pandemic and compare them with IIM patients diagnosed before COVID-19.

Methods: We retrospectively analysed the medical records of adult patients (>18 years) who were diagnosed with IIM during COVID-19 versus a control group of patients diagnosed before the outbreak. Included were patients whose diagnosis was made at the Department of Medicine and Rheumatology Unit of Hadassah Medical Center, Jerusalem, Israel. We also conducted a comprehensive review of the literature regarding SARS-CoV-2 infection and vaccine-induced IIM.

Results: Our study yielded 18 and 16 diagnosed IIM patients over periods of 27 and 56 months in the COVID-19 and pre-pandemic cohorts, respectively. These constitute incidence rates of 0.66 and 0.28 patients/month, respectively, marking an increased rate in the COVID-19 group. Unique features were noted in IIM patients who were diagnosed during the pandemic. This includes male predominance (M:F ratio of 12:6), higher hospitalisation rate (0.77 vs. 0.43 admitted/total patients) and increased number of patients with CPK >10,000 U/L (3 vs. 1 patient). Despite the more severe presentation and course in the pandemic group, survival was comparable between the groups.

Conclusions: The incidence of IIM increased during the COVID-19 pandemic. These patients display unique features and a more severe presentation. Fortunately, the prognosis remains unchanged.