Characteristics and risk factors of lymphoproliferative disorders among patients with rheumatoid arthritis concurrently treated with methotrexate: a nested case-control study of the IORRA cohort.

The purpose of the study is to demonstrate the characteristics of lymphoproliferative disorders (LPDs) in patients with rheumatoid arthritis (RA) and risk factors for LPD among RA patients concurrently treated with methotrexate (MTX). Among patients who participated in the Institute of Rheumatology, Rheumatoid Arthritis (IORRA) cohort study in October 2010, past existence of LPD from patient's report was confirmed through medical charts. Background factors, LPD pathological findings, and the clinical courses of LPD and RA after LPD were assessed. To analyze the risk of MTX-associated LPD among RA patients concurrently treated with MTX, a nested case-control study design was used to select control patients who had received MTX but did not develop LPD by matching calendar date, sex, and age (within 5 years) at a 1:10 ratio. Odds ratios (ORs) with 95% confidence intervals (95% CIs) for occurrence of LPD were analyzed by multivariate analysis. Forty-eight patients experienced LPD among 5757 patients, and 25 (52.1%) of those had lymphoma. LPD regressed in 60.4% of all LPD patients and 24.0% of lymphoma patients. In the 26 cases who developed LPD during MTX treatment, multivariate analysis revealed that 28-joint disease activity score (DAS28) (OR 1.57 [95% CI, 1.12-1.57]; p < 0.01) and lactate dehydrogenase (LDH) level (OR 1.01 [95% CI, 1.00-1.02]; p < 0.01), but not concomitant dose of MTX, were risk factors for LPD. Among RA patients concomitantly treated with MTX, high disease activity, but not MTX dose, was a risk factor for the occurrence of LPD.