# Is the Development of Hypo-Gammaglobulinemia Associated with Better Treatment Response in Patients with Rheumatoid Arthritis Using Rituximab?

## TL;DR

This study found that 21% of rheumatoid arthritis patients treated with rituximab developed low antibody levels, but this did not affect their disease activity scores.

## Contribution

The study identifies risk factors for hypogammaglobulinemia and suggests acute phase reactants may better reflect treatment response than DAS28-ESR.

## Key findings

- 35 out of 165 patients (21.2%) developed hypogammaglobulinemia after rituximab treatment.
- Pre-treatment IgG levels below 10.5 g/l and more RTX courses increased hypogammaglobulinemia risk.
- CRP levels were significantly lower in patients with hypogammaglobulinemia, but DAS28-ESR scores were similar.

## Abstract

Objectives: To determine the frequency of development of hypogammaglobulinemia in rheumatoid arthritis (RA) patients receiving rituximab (RTX) and to examine the relation between the development of hypogammaglobulinemia and RTX treatment response. Methods: The data of 165 RA patients who applied to our outpatient clinic between January 2010 and June 2021, and who received at least 2 courses of RTX with an interval of 6 months, were retrospectively evaluated. The demographic, clinical, and laboratory data, as well as treatment characteristics, were collected. Results: Of 165 patients, 35 (21.2%) developed hypogammaglobulinemia. In the multivariable analysis examining the risk factors for the development of hypogammaglobulinemia in RA patients receiving RTX, it was determined that having pre-treatment IgG value below 10.5 g/l (OR= 4.24 (95% CI 1.69–10.66) and the increase in the number of RTX courses (OR= 1.1 (95% CI 1.01–1.22) were independently associated risk factors. During their follow-up, patients who developed hypogammaglobulinemia and those who did not were compared. No difference was observed between DAS28-ESR levels, but CRP levels were significantly lower in the group that developed hypogammaglobulinemia. Conclusions: In this study, there was no difference in DAS28-ESR levels between patients with and without hypogammaglobulinemia, although a difference was observed in acute phase reactants, which are more objective parameters. This may be due to subjective parameters in DAS28-ESR scoring or other concomitant conditions such as fibromyalgia. Therefore, additional objective findings or methods may guide the evaluation of treatment response.