Impact of rituximab on IgG and IgM levels in patients with autoimmune bullous diseases: a cohort study.

Rituximab (RTX) causes hypogammaglobulinemia in a variety of autoimmune diseases. However, the exact incidence and clinical significance in patients with autoimmune bullous diseases (AIBD) remain undetermined. In this cohort study, we enrolled patients with AIBD treated with RTX at a tertiary dermatology center between 2019 and 2021. Serum IgG and IgM levels, cumulative RTX dosage, and other factors were measured at baseline and during a follow-up visit. We used multivariate linear regression to assess the effect of RTX on immunoglobulin levels over time, adjusting for factors such as cumulative RTX dose, time since last infusion, and steroid use. Hypogammaglobulinemia was defined as IgG < 600 mg/dL and IgM < 40 mg/dL. Logistic regression was employed to evaluate adjusted risk factors for developing hypogammaglobulinemia. Age at first infusion was negatively correlated with both IgG (p < 0.0001) and IgM levels (p = 0.002). Total cumulative RTX dosage was negatively associated with IgM levels (p < 0.001). Daily steroid dosage was positively correlated with IgM levels (p = 0.023). Mycophenolate mofetil was associated with lower IgG levels (p = 0.029). Daily steroid dosage was found to be associated with a lower risk of hypo-IgM development (p = 0.0497). No serious infusion-related adverse effects or mortality were observed. There were four cases of infection with no association with cumulative RTX dosage (p = 0.299). Our study shows an association between RTX and lower serum IgM levels in patients with AIBD, highlighting the need to assess serum immunoglobulin levels before RTX therapy to optimize its use and minimize adverse effects.