A case of rheumatoid pericarditis associated with a high IL-6 titer in the pericardial fluid and tocilizumab treatment.

We report a 60-year-old woman with rheumatoid arthritis complicated by pericarditis. Treatment with tocilizumab improved her polyarthritis, but the pericardial effusion increased so rapidly as to cause cardiac tamponade before the treatment could prove its efficacy. Pericardial effusion disappeared after pericardiocentesis. The pericardial fluid contained a remarkably high concentration of interleukin-6 (IL-6; 351,000 pg/mL), which tocilizumab appeared to have made yet higher compared to the reported IL-6 levels in rheumatoid pericarditis. No further exacerbation of pericarditis was observed after retreatment with tocilizumab. This case has important implications in that it suggests that the prominently elevated IL-6 level in pericardial fluid during tocilizumab treatment may be an indicator of its efficacy for pericarditis.