Trends and in-hospital outcomes of multiple myeloma in autoimmune rheumatic disease hospitalizations: A National Inpatient Sample analysis, 2016–2022.

e19577 Background: Multiple myeloma (MM) is associated with immune dysregulation and substantial inpatient morbidity. Autoimmune rheumatic diseases (ARDs), including systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis, Sjögren syndrome, and vasculitis, may further modify MM outcomes through chronic inflammation and immunosuppressive therapy. Contemporary national data describing temporal trends and inpatient outcomes of MM among ARD patients are limited. We evaluated national trends, inpatient outcomes, and resource utilization in MM hospitalizations with ARDs. Methods: We analyzed the National Inpatient Sample (2016–2022) using survey-weighted methods. Adult ARD hospitalizations were stratified by MM status. Temporal trends were assessed using year as a continuous variable. Outcomes included in-hospital mortality, sepsis, acute kidney injury (AKI), dialysis, disseminated intravascular coagulation (DIC), venous thromboembolism (DVT), anemia, thrombocytopenia, and tumor lysis syndrome (TLS). Multivariable survey logistic regression adjusted for demographics, comorbidities, and hospital factors. Results are reported as adjusted odds ratios (aOR) with 95% confidence intervals (CI). Results: Among an estimated 6.21 million ARD hospitalizations, 0.39% involved MM. MM prevalence increased from 0.31% in 2016 to 0.41% in 2022, with each year associated with a 3.9% higher odds of MM (aOR 1.04, 95% CI 1.02–1.06; p<0.001).MM patients were older (70.9 vs 65.4 years; p<0.001) and predominantly female (p<0.001). In-hospital mortality among MM hospitalizations rose from 2.8% to 3.6%, increasing 7.1% per year after adjustment (aOR 1.07, 95% CI 1.06–1.08; p<0.001). Compared with ARD hospitalizations without MM, MM was independently associated with higher odds of sepsis (11.9% vs 9.7%; aOR 1.19, 95% CI 1.08–1.30), AKI (34.2% vs 20.2%; aOR 1.79, 95% CI 1.67–1.91), DIC (0.53% vs 0.21%; aOR 2.36, 95% CI 1.59–3.50), DVT (4.9% vs 2.9%; aOR 1.59, 95% CI 1.39–1.83), anemia (62.5% vs 37.8%; aOR 2.51, 95% CI 2.36–2.67), thrombocytopenia (14.5% vs 6.3%; aOR 2.40, 95% CI 2.20–2.62), and TLS (0.51% vs 0.04%; aOR 11.89, 95% CI 7.95–17.80; all p<0.001). MM hospitalizations had longer length of stay (6.96 vs 5.45 days) and higher total charges ($84,594 vs $68,796). Conclusions: Hospitalizations involving MM among patients with ARDs are increasing and are associated with rising mortality, complication burden, and healthcare utilization. These findings highlight the need for early risk stratification and integrated oncologic-rheumatologic inpatient care.