Abstract
Methotrexate (MTX) is an established anchor drug used for the treatment of rheumatoid arthritis. Patients receiving MTX are at an increased risk of developing MTX-associated lymphoproliferative disorders (MTX-LPDs). A diagnosis of MTX-LPD requires a pathological evaluation; however, biopsy samples are often unavailable because of the anatomical location of the lesions and their rapid regression following MTX withdrawal. In cases in which a biopsy is not feasible, biomarkers may aid in predicting the responsiveness to MTX cessation. This report describes a case of MTX-associated systemic lymphadenopathy characterized by a marked elevation in the serum IgG4 concentration. These findings suggest the potential role of serum IgG4 as a novel biomarker of MTX-LPD.