Methotrexate-Associated Systemic Lymphadenopathy Exhibiting a Marked Elevation of the Serum IgG4 Concentrations.

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.