Systemic Juvenile Idiopathic Arthritis (SJIA) is a rare subtype of juvenile idiopathic arthritis (JIA), also known as Still’s Disease. “Systemic” means it may affect not only the joints but other parts of the body, including the liver, lungs, and heart.
Systemic – Of or relating to a system (body)
Juvenile – In a young person, typically under the age of 18
Idiopathic – Disease with no known cause or origin
Arthritis – Inflammation of a joint
There are 7 different types of JIA, SJIA is the most serious and sometimes lethal type, making up 10% – 15% of the JIA population. SJIA also differs from other subtypes of JIA in that it is considered an auto-inflammatory disease rather than auto-immune disease.
Macrophage Activation Syndrome (MAS) and Interstitial Lung Disease (ILD)
Macrophage Activation Syndrome (MAS), is a life- threatening and the most serious potential complication of SJIA. It has been described as a hyperinflammatory cytokine storm. MAS can occur in any rheumatic disease, but for reasons that are unclear, an estimated 80% of cases are associated with SJIA. MAS is the leading cause of death in SJIA, with mortality as high as 10% – 20% according to research.
Interstitial Lung Disease (ILD) is an umbrella term for a group of diseases that cause lung tissue to become scarred. Lung disease associated with SJIA is characterized by life-threatening chronic pulmonary manifestations and distinctive clinical features. SJIA-ILD while not well understood can be rapidly progressive and lethal.