Abstract
Biologics play a key role in the treatment of rheumatoid arthritis (RA), while RA-related serious infection remains an unsettled clinical problem. Detection of tuberculosis (TB) is challenging due to the difficulty in distinguishing symptoms such as fever and elevation of inflammatory markers from other infections or a disease flare of RA. The expression of the CD64 molecule on neutrophils (neutrophil CD64) was upregulated by various infections including TB. However, it was not affected by disease activity of RA or by any therapy against RA. The present article reports three cases of extrapulmonary TB which occurred in patients with RA undergoing treatment with biologics. The marked increase in the levels of neutrophil CD64 may provide important insight into the diagnosis of TB.