Key Points
` Systemic juvenile idiopathic arthritis accounts for approximately 4-15% of
juvenile idiopathic arthritis (JIA) and is defined as arthritis in ≥1 joint for
≥6 weeks in a child age <16 years with or preceded by fever of ≥2 weeks
that is documented to be daily ("quotidian") for ≥3 days and accompanied
by one or more of the following: evanescent erythematous rash, generalized
lymphadenopathy, hepatomegaly or splenomegaly, and serositis.
` The goal of therapy for systemic JIA is similar to that of the other categories
of JIA, and focuses on the prompt control of active inflammation and
symptoms and the prevention of a number of disease- and/or treatment-
related morbidities such as growth disturbances, joint damage, and
functional limitations.
` Many children with systemic JIA have a particularly refractory course, with
persistent disease associated with a high risk of joint damage and severe
growth impairment.
` The inflammatory process underlying systemic JIA appears to be distinct
from other categories of JIA, with a central role for both interleukin-1 (IL-1)
and IL-6.
` Approximately 10% of children with systemic JIA develop overt
clinical features of macrophage activation syndrome (MAS), a life-
threatening condition characterized by fever, organomegaly, cytopenias,
hyperferritinemia, hypertriglyceridemia, hypofibrinogenemia, and
coagulopathy, among other findings.
` The mortality rate for children hospitalized with systemic JIA and MAS is
estimated to be as high as 6% but may be even higher based on estimates
from case series.
