Sex differences in idiopathic inflammatory myopathies: insights from a large multicentre observational study

OBJECTIVES: Preliminary evidence suggests sex-related variations in clinical and serological features in idiopathic inflammatory myopathies (IIMs), yet comprehensive cohort studies, particularly within the Italian population, remain scarce. The aim of this study is to assess sex differences in clinical phenotype, serological features, and disease activity, and to identify independent associated factors of disease activity in a well-characterised multi-centre Italian IIMs cohort. METHODS: A total of 228 IIMs patients from 5 tertiary Rheumatology Units across Italy were included. Demographic, clinical, serological, and treatment data were collected. Continuous variables are reported as mean ± SD or median (IQR), categorical variables as n (%). Comparisons between the 2 sexes were assessed by Student's t-test, Mann-Whitney U test, χ², or Fisher's exact test. Independent associated factors of disease activity (MYOACT) were assessed through multivariable linear regression analysis. RESULTS: Of 228 patients, 157 (68.9%) were female, and 71 (31.1%) were male. Age at diagnosis was similar between sexes. Males showed significantly higher disease activity measured by the MYOACT index. Multivariable analyses identified male sex, MDA5 autoantibody positivity, and greater disease damage extent as independent associated factors of higher disease activity, whereas dermatomyositis and polymyositis were associated with lower disease activity. Furthermore, MYOACT showed good predictive ability to define patients at risk for intensive care unit admission with an optimal threshold of 0.23. CONCLUSIONS: These findings highlight relevant sex-related differences in clinical expression and may support more personalised management strategies.