The phenomenon of neutropenia during tocilizumab therapy in patients with juvenile idiopathic arthritis

Tocilizumab (TCZ) is one of the biological agents that are most commonly used in the treatment of juvenile idiopathic arthritis (JIA), especially its systemic variant. The development of neutropenia, which is associated with the use of TCZ and its mechanism of action, requires a detailed study. Based on the analysis of their own results and comparison of the latter with the data available in the literature, the authors analyze the aspects of development of neutropenia during TCZ therapy. Objective: to analyze all cases of neutropenia with the use of TCZ in polyarticular (pJIA) and systemic (sJIA) variants of the disease. Subjects and methods. The open-label prospective study enrolled 27 patients with pJIA and 83 patients with sJIA, who were resistant to prior standard therapy. The treatment duration was 4 to 84 months (median, 22 months for pJIA; 34 months for sJIA). The frequency and timing of neutropenia and the relationship to infection and concomitant/previous therapy were examined. Results and discussion. 22 and 62 patients with pJIA and sJIA, respectively, continued treatment; its median duration was 27.4 [9; 72] months. 7 patients with pJIA and 21 with sJIA, discontinued TCZ due to severe adverse events (n=2 and n=11, respectively) and organizational reasons (n=5 and n=7); in sJIA, therapy was discontinued for sustained remission in two patients and for secondary inefficiency in one patient. At least one episode of neutropenia was observed in 63% of patients with pJIA and in 48.2% of those with sJIA; among them, there was grade 1 neutropenia in 5 and 15 patients, respectively; grade 2 in 6 and 15, grade 3 in 4 and 10, and grade 4 in two patients with pJIA. Neutropenia was more frequently observed in the first months of therapy for pJIA; that was seen in patients with sJIA when the latter reached its inactive status. In 5 patients with sJIA, neutropenia was recorded as a manifestation of macrophage activation syndrome (MAS); no correlation with TCZ infusions was found. Neutropenia was not associated with an increased rate of infections. The use of methotrexate was not significantly related to the low level of neutrophils, whereas the earlier age was associated with the degree and frequency of neutropenia. All cases of neutropenia were recorded in patients with a therapeutic response rate of >50% according to the American College of Rheumatology Pediatric (ACR Pedi) criteria. The findings suggest that there are different mechanisms and periods of neutropenia during TCZ therapy for JIA: 1) benign, transient neutropenia, a predictor of the high efficiency of therapy, develops primarily in the first few days after infusion; 2) neutropenia as a phenomenon of «redundancy» of therapy (more resistant) develops more often in the inactive phase of the disease; 3) neutropenia as a component of MAS, which is associated with its other markers. No relationship was found between neutropenia and an increased risk of infections. TCZ-treated patients need careful clinical and laboratory monitoring, including consideration of a risk for neutropenia and subsequent individual treatment when this condition is identified.