Method: RA patients who had inadequate response to MTX and/or TNF inhibitor were treated by 8mg/kg of tocilizumab every 4 weeks. Serum IL-6 and CRP levels and DAS28 score of them were examined at baseline and every 4 weeks at tocilizumab injection. Patient's myalgia was evaluated everyday by themselves using 0 to 100 mm visual analog scales (VAS). The serum levels of creatine kinase (CK), aldolase, and TNF-α were also examined in addition to regular blood tests.
Result: Seventy-six RA patients were treated with tocilizumab every 4 weeks. Of these patients, 28 complained myalgia which started one or two days after receiving tocilizumab injection and decreased gradually, but the myalgia recurred by further tocilizumab injections. They suffered from severe myalgia of upper body such as neck, shoulder, and back muscles, but these pains were quite different from those of fibromyalgia nor polymyalgia rheumatica. When the patients complained myalgia, the levels of CRP had decreased to basal levels (less than 3 mg/L) and their activities of rheumatoid arthritis such as the number of swelling joints were rather decreased. RA patients with high disease activity at initial tocilizumab treatment developed myalgia more frequently than those with low disease activity. In the patients experienced myalgia, the serum IL-6 levels were significantly higher (107 ± 56 pg/L) than those in patients without myalgia (31 ± 18 pg/L) at 28 days after initial tocilizumab treatment. But the serum levels of high sensitive TNF-α and CRP were decreased to within normal limits, and the levels of CK or aldolase were within normal range. After initial tocilizumab treatment, the magnitude of myalgia decreased well paralleled with serum IL-6 levels.
Conclusion: During tocilizumab treatment, RA patients with high disease activities frequently experienced myalgia in spite of decreasing the disease activities. In the patients who complained myalgia, the levels of IL-6 but not CRP or TNF-α were selectively high. However, before tocilizumab treatment, the patients did not complain myalgia, when both IL-6 and CRP levels were high, suggesting the myalgia supposed due to interaction of IL-6 and tocilizumab.
Disclosure: O. Saiki, None; H. Uda, None.