Serum IL-6 level trajectory for predicting the effectiveness and safety of tocilizumab in the treatment of refractory Takayasu arteritis

Aim To explore the value of serial monitoring of serum interleukin-6 (IL-6) levels for predicting treatment response and occurrence of adverse events during tocilizumab (TCZ) treatment in refractory Takayasu arteritis (TAK). Methods TAK patients receiving TCZ treatment were prospectively recruited and followed up at 1 month, 3 months and then every 3–6 months. Serum IL-6 levels were measured at each visit. Overall response was the combination of complete and partial response, requiring resolution of signs and symptoms, hsCRP and ESR level decreased at least by half, no progression on imaging and dose of glucocorticoid <15 mg/d. Results Thirty-five patients with a median follow up duration of 17 [9–44] months were included. The change of IL-6 after TCZ treatment for 6 months compared to the baseline was significantly lower in patients achieved overall response at 6, 12, 18 and 24 months. The ratio of IL-6 at 6 months to baseline could predict overall response at 12 and 24 months after TCZ treatment. With a cutoff value of 1.6, the sensitivity and specificity were 83.3 % and 87.5 % for 12 months, while 100 % and 88.9 % for 24 months. Patients with the ratio less than 1.6 were also 9 times more likely to achieve sustained improvement without treatment intensification. No correlation between IL-6 dynamics and occurrence of adverse events was found. Conclusions The change of IL-6 levels after TCZ treatment for 6 months compared to the baseline can predict the overall treatment response at 12 months, 24 months and sustained improvement.