Benign, atypical and malignant lymphoproliferative disorders in rheumatoid arthritis patients

Lymphadenopathy, which may be associated with systemic symptoms, is frequently associated with rheumatoid arthritis (RA). Reactive non-neoplastic tissue comprises the majority of the lymph node lesions. However, several cohort studies have demonstrated that RA has an increased risk of non-Hodgkin's lymphomas (NHLs). Since the early 1990s, an atypical or malignant lymphoproliferative disorders (LPD) in patients immunosupressed with methtorexate (MTX) therapy for RA has been emphasized, namely MTX-associated LPDs. Epstein–Barr virus (EBV) has received attention in connection with the etiology of RA. The present review describes the clinicopathologic and immunohistochemical findings of reactive, atypical and malignant LPDs associated with RA along with the presence or absence of EBV in LPDs using the in situ hybridization (ISH) method. The majority of reactive lymph node lesions exhibit reactive follicular hyperplasia with interfollicular polyclonal plasmacytosis. Atypical LPDs rarely appears in RA patients. However, these cases occasionally pose difficult problems in the differential diagnosis from malignant lymphomas associated with RA or atypical and malignant LPDs showing RA-like clinicopathological findings. Clinicopathologically, three types of atypical LPDs have delineated, i.e. (i) resembling multicentric Castleman’s disease (MCD); (ii) atypical paracortical hyperplasia with lymphoid follicles (APHLF) and; (iii) atypical lymphoplasmacytic immunoblastic proliferation. Malignant lymphoma associated with RA is characterized by; (i) predominance of elderly cases; (ii) usually female predominance, reflecting the sex ratio of RA; (iii) longstanding history of RA; (iv) relatively frequent advanced stage of disease; (v) majority of the patients had the B-cell phenotype; and (vi) an increased frequency of diffuse large B-cell lymphoma (DLBCL) in RA. It is unlikely that EBV is the causative agent of either reactive or atypical LPD. Among malignant lymphomas, EBV-associated lymphoma comprised only a small fraction of all NHLs in the general RA patient population.