Objectives: Schnitzler's syndrome is a rare autoinflammatory disease. Clinical response to IL-1 inhibitor drugs has been described, but limited information is available on the long-term efficacy and safety of these agents in Schnitzler's syndrome. Methods: A retrospective study was conducted of patients with Schnitzler's syndrome fulfilling Strasbourg diagnostic criteria followed in 9 Italian centres. The retention rate of IL-1 inhibitors was evaluated using Kaplan-Meier analysis. Results: Fifteen of 20 patients with Schnitzler's syndrome were treated with IL-1 inhibitors: in total, they received 16 courses of anakinra (median duration 20.0 months [6.0-58.3]), and 8 courses of canakinumab (median duration 19.0 months [13.5-31.0]). The retention rate of IL-1 inhibitors was 73.4% [SE 9.4] at 1 year and 63.6% [SE 10.4] at 2 years. There was no significant difference between the retention rate of anakinra and canakinumab. The retention rate was higher in patients with a definite diagnosis according to the Strasbourg criteria as compared with those with a probable diagnosis (p=0.03). At the last follow-up visit, all patients who started therapy with IL-1 inhibitors were still on treatment, although in some cases with an increased dosage compared to the start of therapy. A sparing effect on the use of conventional synthetic disease-modifying anti-rheumatic drugs and a significant reduction of prednisone dosage (p=0.02) and of serum amyloid A (SAA) levels (p=0.03) were observed. Conclusions: The retention rate of IL-1 inhibitors in patients with Schnitzler's syndrome was high, particularly in patients with a definite diagnosis according to the Strasbourg criteria, reflecting their effectiveness in the treatment of this syndrome.
