Ab0161 Rituximab in Rheumatologic Diseases: Hypogammaglobulinemia as a Side Effect

Background: Rituximab (RTX), is a widely used anti-CD20 monoclonal antibody in rheumatologic diseases. RTX is a biological agent whose efficacy has been demonstrated in rheumatoid arthritis (RA) and Anca-associated vasculitis (AAV) through randomized controlled trials. Its effectiveness has been confirmed in open-label studies and case series in other connective tissue diseases such as systemic lupus erythematosus (SLE), dermatomyositis (DM), and systemic sclerosis (SCL). RTX can be considered a safe and effective treatment option in these conditions. The nature of the disease increases the risk of infection itself, but it is important to keep in mind that the applied treatment can increase the infection risk as well. Objectives: We investigated patients at our tertiary center who developed hypogammaglobulinemia as a side effect of rituximab treatment. Methods: We made a retrospective evaluation of rheumatological patients who used RTX. Levels of IgG lower than 700mg/dl were defined as hypogammaglobulinemia. Patients' diagnosis, demographic and clinical data were acquired from patients' files. The number of RTX courses, how many courses caused hypogammaglobulinemia, and differences between IGG levels before and after RTX were evaluated. 6-month treatment before RTX and the concomitant treatment were evaluated. The treatment after hypogammaglobulinemia (increasing the interval between the administrations, discontinuation, dosage reduction, and single dosage application) was noted. Hospital admissions and death cases among patients who developed hypogammaglobulinemia were noted. We retrospectively examined the number of courses and hypogammaglobulinemia levels in patients treated with rituximab for autoimmune diseases. We also assessed the risk of infections associated with these cases. Results: We included 30 patients who experienced hypogammaglobulinemia due to RTX treatment, of which 19 (63.3%) were female, and the mean age of patients was 52.4±12.9 years. Among the patients treated with RTX, 10 had a diagnosis of AAV, 8 diagnoses of RA, 6 were diagnosed with SLE, one with Sjogren, one with scleroderma, and one with retroperitoneal fibrosis. All of the patients (30) were treated with at least one course of RTX and the mean of the number of applied courses was 6.8±4.1. Data on IgG levels before and after RTX was known in 24 patients, where the mean of the levels before the treatment was 770±410 mg/dl and after the RTX was 505±133.3 mg/dl (p=.0.004). In 9 patients, IgG levels dropped below 500mg/dl. The interval between administrations was increased in 8 (26.6%) patients, the dosage of RTX was reduced in 3 (10%) patients, and 6 (20%) patients were treated with a single dosage.6 (20%) patients were treated with intravenous immunoglobulin (IVIG). The number of patients who discontinued the medication due to hypogammaglobulinemia was 6 (20%), and 4 (13.3%) were hospitalized due to infection secondary to hypogammaglobulinemia. Conclusion: Despite its high effectiveness, Rituximab can lead to hypogammaglobulinemia, necessitating careful monitoring. In rheumatological cases where replacement therapy is required, IVIG treatment can be continued to manage hypogammaglobulinemia. In patients who develop hypogammaglobulinemia due to RTX, careful monitoring for potential infection disease development is required. REFERENCES: 1 Tieu J, Smith RM, Gopaluni S, et al. Rituximab Associated Hypogammaglobulinemia in Autoimmune Disease. Front Immunol. 2021;12:671503. Acknowledgements: NIL. Disclosure of Interests: None declared.