Trends in Hospitalizations of Patients with Idiopathic Inflammatory Myopathies: Long-Term Observational Study, 2010-2024.

Background/Objectives: Idiopathic inflammatory myopathies (IIMs) are very rare, chronic, immune-mediated diseases that clinically manifest with myositis symptoms and extramuscular manifestations. The rarity of the disease makes it difficult to conduct double-blind studies, and large population-based studies are needed to improve our knowledge of them. This study aims to analyze the hospitalization rates and trends of IIMs between 2010 and 2024. Additionally, a characterization of the IIM patient population in Poland was conducted. Methods: A retrospective study using data from the Nationwide General Hospital Morbidity Study (NGHMS) between 2010 and 2024 was conducted. Data included demographic characteristics, principal diagnosis, hospitalization, and in-hospital mortality. Classification in accordance with ICD-10 was applied. A total of 7139 patients were included. Appropriate descriptive analyses, comparative tests, Poisson regression for incidence trends, and logistic regression for mortality predictors were performed, with p < 0.05 considered statistically significant. Results: The median IIM incidence in the Polish population was 1.209 per 100,000 per year. The overall female-to-male ratio was 1.68. Hospitalization and mortality trends for IIM were stable over the time period. The incidence among voivodeships in Poland was comparable. Conclusions: Nationwide, comprehensive data are an extremely valuable tool for researching and understanding diseases as rare as IIMs. The incidence, hospitalization, and mortality rates of IIMs in Poland were stable between 2010 and 2024.