AMETHYST : a Retrospective Cohort Study of Treatment Patterns and Outcomes in Patients With Glucocorticoid‐refractory Macrophage Activation Syndrome Complicating Still's Disease

OBJECTIVE: Information is limited on the natural history and current treatment patterns in macrophage activation syndrome (MAS), a life-threatening hyperinflammatory syndrome complicating Still's disease (systemic juvenile idiopathic arthritis [sJIA] and adult-onset Still's disease [AOSD]). AMETHYST aimed to describe real-world treatment patterns and outcomes in glucocorticoid (GC)-refractory MAS complicating Still's disease. METHODS: In this retrospective cohort study, medical data from January 1, 2012, to March 31, 2023, were abstracted from charts of all eligible patients across eight sites in Europe, Canada, and the US for index MAS episodes (occurring between January 1, 2012, and September 30, 2022, and meeting eligibility criteria). RESULTS: Overall, 55/64 (86%) included patients had sJIA and 9/64 (14%) had AOSD. Most patients (53/64 [82.8%]) were children at index (median age: 7.0 years). MAS was characterized by rash (60.4%), fever (52.8%), and hepatic involvement (49.1%). All patients received GCs; most were also treated with anakinra (48/64 [75%]) and/or ciclosporin (33/64 [51.6%]). Normalization of 7 (complete MAS laboratory remission) or ≥3 (partial remission) prespecified laboratory parameters occurred in 7/64 (10.9%) and 41/64 (64.1%) patients, respectively. GCs were tapered in 50/64 (78.1%) patients (median: 39.9 days). Per investigator assessment of clinical signs/symptoms for the index MAS episode, 24/64 (37.5%) and 26/64 (40.6%) patients had a complete and partial response, respectively. MAS recurred in 20/64 (31.3%) patients. There were 7/64 (10.9%) deaths; estimated 1-year survival probability was 93.75%. CONCLUSIONS: Low MAS laboratory remission rates and toxicities of high-dose GCs combined with other treatments highlight the need for safer, more effective therapies.