Pediatric emergency medicine trisk 2979 2979
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Current Evidence
JIA, formerly known as juvenile rheumatoid arthritis (JRA), is now the most common
pediatric rheumatologic disease in the developed world, having replaced acute
rheumatic fever. JIA occurs in all races and ethnic groups, with a reported prevalence
that varies from 30 to 400 per 100,000 children depending upon the population studied
and the diagnostic techniques used. In the United States alone, JIA affects at least
100,000 children.
A variety of different classification systems for JIA exists, but in the absence of a
clear-cut understanding of the pathogenesis of arthritis, the preferred is the
International League for Associations in Rheumatology (ILAR) classification system (
Table 101.10 ). It includes the following subtypes of arthritis: polyarticular,
oligoarticular (persistent and extended), and sJIA as well as psoriatic arthritis,
enthesitis-related arthritis (ERA), and undifferentiated arthritis ( Table 101.11 ).
Persistent unexplained arthritis of one or more joints lasting more than 6 weeks in
children younger than 16 years of age will be referred to as JIA, though this is an
umbrella term that overarches the more specific subtypes. In all cases, because there
are no laboratory abnormalities specific for JIA, the diagnosis is made clinically after
exclusion of other infectious, inflammatory, and traumatic conditions.
The etiology of JIA is not known and is likely multifactorial. Further, systemic JIA is
more aptly characterized as an autoinflammatory disorder (or disorder of the innate
immune system), whereas the other subtypes are more likely to be autoimmune (or
disorder of the adaptive immune system). It is useful conceptually to divide the
pathogenesis of inflammatory arthritis into an initiating phase and a perpetuating phase.
Various events, particularly viral infections, may trigger articular inflammation. For a
variety of reasons related to both the host and the inciting event, a process that is selflimited in most children leads to ongoing inflammation in others. This inflammation is
characterized by abnormal tissue and circulating levels of proinflammatory cytokines
(including interleukin [IL]-1, IL-6, tumor necrosis factor [TNF], and interferon-γ)
leading to activation of lymphocytes and infiltration of synovium. In fact, conditions
labeled as JIA most likely represent a final common pathway for many different types
of synovitis in view of the widely disparate characteristics of the different subtypes of
JIA.
Clinical Considerations
JIA is characterized by wide demographic and clinical variety, so the condition has
been divided into subtypes based on these factors and on the pattern of the disease
during the first 6 months following onset ( Table 101.11 ). These varieties, in turn, are
treated in different ways, and are associated with different complications. Until a
pathophysiologically based means of classifying and distinguishing these subtypes of
JIA becomes available, what is probably several discrete conditions will continue to be
