Prospective monitoring of Epstein–Barr virus and other herpesviruses in patients with juvenile idiopathic arthritis treated with methotrexate and tocilizumab

Methotrexate (MTX) is widely used for the treatment of articular-type juvenile idiopathic arthritis (JIA), but patients receiving MTX for rheumatoid arthritis have been reported to be at increased risk of reactivation of Epstein–Barr virus (EBV) and the development of lymphoproliferative disorder. The association between MTX and reactivation of herpesviruses in pediatric patients is not yet understood. We prospectively monitored the viral load of EBV, cytomegalovirus (CMV), and herpesvirus 6 (HHV-6) in four JIA patients treated with MTX for 12–24 months. Tocilizumab, an anti-interleukin 6 receptor monoclonal antibody, was added to the therapeutic regimen in three patients during the observation period. Prior to the administration of MTX, EBV and HHV-6 were detected by PCR in two patients. Significant increases in EBV and HHV-6 load were not observed following the administration of MTX or tocilizumab. In one patient, a relatively high EBV load remained detectable during 21 months of observation in the absence of clinical symptoms. CMV was not detected throughout the observation period in any patient. This is the first report monitoring the longitudinal DNA loads of EBV and other herpesviruses in JIA patients. EBV and HHV-6 were often detectable, but treatment with MTX and tocilizumab did not appear to influence the viral load.