Macrophage Activation Syndrome (MAS) is a serious condition that can happen in people with Still's disease, a type of arthritis that causes joint pain and fever. This study looks at how MAS, which doesn't get better with glucocorticoids (GC) – medicines that reduce inflammation, is treated in patients with Still's disease. The study is observational, meaning it just looks at past medical records and doesn't involve any new tests or treatments on patients. It includes people from babies as young as 6 months to adults up to 80 years old who had MAS between January 1, 2012, and September 30, 2022. People with a special blood condition called Hemophagocytic Lymphohistiocytosis (HLH) or cancer before they had MAS, or those in other clinical trials, cannot be part of this study.

• No need for extra doctor visits or treatments as the study uses existing medical records.
• It includes patients whose MAS didn't improve with standard GC treatment.
• No compensation or direct benefits as the study is purely observational.